Frequent or continuous topical application of drops or the use of local drug delivery devices has been used to ensure prolonged elevated drug concentrations. Depending on the route of infection, causative organisms commonly include Staphylococci, Streptococci, Haemophilus influenzae, bacillus cereus and Propionibacterium acnes. Bacterial endophthalmitis requires immediate aggressive treatment with antibacterials, usually given intravitreally. A considerable amount of effort has been made in ophthalmic drug delivery since the A number of approaches to the delivery of drugs for ocular treatment has been investigated and proposed.
These range from simple systems such as aqueous suspensions where the viscosity and hence the residence time, has been increased by cellulosic polymer to complex system such as penetration enhancers, external devices collagen shields, Preformed gels, iontophoresis and pumps , ion-exchange resins, liposomes, microspheres and micro particles, polymeric films, inserts, prodrugs, mucoadhesives and metabolism based drug design.
Sprays Although not commonly used, some practitioners use Mydriatics or Cycloplegics alone or in combination in the form of eye spray. These sprays are used in the eye for dilating the pupil or for Cycloplegics examination. Contact lenses Contact lenses can absorb water soluble drugs when soaked in drug solutions. These drug saturated contact lenses are placed in the eye for releasing the drug for a long period of time. The hydrophilic contact lenses can be used to prolong the ocular residence time of the drugs.
Artificial tear inserts A rod shaped pellet of Hydroxy propyl cellulose, without preservative is commercially available Lacrisert. This device is designed as a sustained release artificial tear for the treatment of Dry eye disorder. Filter paper strips Sodium fluorescein and bengal dyes are commercially available as drug- impregnated filter paper strips.
These dyes are used diagnostically to disclose corneal injuries and infections such as herpes simplex and dry eye disorders. Micro emulsion Due to their intrinsic properties and specific structures, microemulsions are a promising dosage form for the natural defense of the eye. Indeed, because they are prepared by inexpensive processes through auto emulsification or supply of energy and can be easily sterilized, they are stable and have a high capacity of dissolving the drugs.
Collagen Shield Collagen is regarded as one of the most useful biomaterials. The excellent biocompatibility and safety is due to its biological characteristics, such as biodegradability and weak antigenicity, these properties made collagen the primary resource in medical applications.
Collasomes show promise among drug delivery systems to the human eye. They are first fabricated from procine scleral tissue, which bears a collagen composition similar to that of the human cornea. The shields are hydrated before they are placed on the eye. Shields are not individually fit for each patient, as are soft contact lenses and therefore, comfort may be problematic and expulsion of the shield may occur.
Ocular Iontophoresis Iontophoresis is the process in which direct current drives ions into cells or tissues. When iontophoresis is used for drug delivery, the ions of importance are charged molecule of the drug. But the role of iontophoresis in clinical ophthalmology remains to be identified. Liposomes Liposomes are phospholipid lipid vesicles for targeting drugs to the specific sites in the body; provide the controlled and selective drug delivery and improved bioavailability.
Liposomes offer the advantages of being completely biodegradable and relatively non toxic but are less stable than particulate polymeric drug delivery systems. Niosomes In order to circumvent the limitations of liposomes, such as chemical instability, oxidative degradation of phospholipids, cost and purity of natural phospholipids, niosomes have been developed as they are chemically stable compared to liposomes and can entrap both hydrophilic and hydrophobic drugs.
They are non toxic and do not require special handling techniques. Mucoadhesive Dosage Forms The successful development of fewer mucoadhesive dosage forms for ocular delivery still poses numerable challenges. This approach relies on vehicles containing polymers, which will attach via noncovalent bonds to conjuctival mucin. Nanoparticles and Microparticles Particulate polymeric drug delivery systems include micro and nanoparticles.
The upper size limit for microparticles for ocular delivery is about mm, above this size; a scratching feeling in the eye can result after ocular application. After optimal drug binding to microspheres or nanoparticles, the drug absorption in the eye enhanced significantly in comparison to eye drops.
Currently, two groups of hydrogels are distinguished, namely preformed and in situ forming gels. Preformed hydrogels can be defined as simple viscous solutions which do not undergo any modifications after administration. In situ forming gels are formulations applied as solutions, sols or suspensions that undergo gelation after instillation due to physicochemical changes inherent to the eye. In this way, the polymers which show sol-gel phase transition and thus trigger drug release in response to external stimuli are the most investigated.
In situ hydrogels are providing such sensor properties and can undergo reversible sol-gel phase transitions upon changes in the environmental condition. These intelligent or smart polymers play important role in drug delivery since they may dictate not only where a drug is delivered, but also when and with which interval it is released.
It should be capable of adherence to mucus. It should have pseudo plastic behaviour. It should have good tolerance and optical clarity. It should influence the tear behaviour. The polymer should be capable of decreasing the viscosity with increasing shear rate there by offering lowered viscosity during blinking and stability of the tear film during fixation.
The Poloxamers consist of more than 30 different non ionic surface active agents. These polymers are ABA-type tri block copolymers Fig. The Poloxamer series covers a range of liquids, pastes and solids with molecular weights and ethylene oxidepropylene oxide weight ratios varying from to 14, and to The gelation mechanism of Poloxamer Fig. Ultrasonic velocity, light-scattering and small-angle neutron scattering measurements of aqueous Poloxamer solutions have clearly indicated a micellar mode of association.
Micelle formation occurs at the critical micellization temperature as a result of PPO block dehydration with increasing temperature, micellization becomes more important and at a definite point, micelles come into contact and no longer move. In addition, the formation of highly ordered structures, such as cubic crystalline phase, has been proposed as the driving force for gel formation, but this hypothesis has been questioned recently.
Thermo reversible gels can be prepared with naturally occurring polymers. Most natural polymer aqueous solutions form a gel phase when their temperature is lowered. Classic examples of natural polymers exhibiting a solgel transition include gelatin and carrageenan. At elevated temperatures these polymers adopt a random coil conformation in solution.
Upon cooling, a continuous network is formed by partial helix formation. Xyloglucan a polysaccharide derived from tamarind seed, forms thermo responsive gels in water, under certain conditions. Xyloglucan is approved for use as a food additive. However, its relatively low transition temperature 0 C makes handling at room temperature problematic. Cellulose acetate derivatives are the only polymer known to have a buffer capacity that is low enough to gel effectively in the cul-de-sac of the eye.
Cellulose acetate phthalate latex is a polymer with potentially useful properties for sustained drug delivery to the eye because latex is a free running solution at a pH of 4. But the low pH of the preparation can elicit discomfort in some patients. The manufacturer states that Carbopol gel has the lowest cross-linking density, while Carbopol intermediate and Carbopol have the highest, higher the cross linking ability more stiff is the gel formed.
All pH-sensitive polymers contain pendant acidic or basic groups that either accept or release protons in response to changes in environmental pH. Swelling of hydrogel increases as the external pH, increases in the case of weakly acidic anionic groups, but decreases if polymer contains weakly basic cationic groups Fig. Some of examples of that are delivered by pH sensitive method includes Ciprofloxacin, 1 Indometacin, 35 Gatifloxacin 36 etc.
Ion sensitive in situ gels Polymers may undergo phase transition in presence of various ions. Some of the polysaccharides fall into the class of ion-sensitive ones. The polysaccharide can be produced by aerobic fermentation and then isolated from the fermentation broth by alcohol precipitation. The polymer backbone consists of glucose, glucuronic acid and rhamnose in the molar ratio On contact with cations in tear fluid the formulation will form a clear gel.
Several models have been presented to explain gellan gum gelation. Mechanism involved in sol to gel transistion by gelrite is as follows, in an ion free aqueous medium, Gelrite forms double helices at room temperature. This solution has a viscosity close to that of water and the helices are only weakly associated with each other by van der waals attraction. When gel-promoting cations are present, some of the helices associate into cation-mediated aggregates, which cross-link the polymer.
On heating the polysaccharide in an ion free environment, the polysaccharide becomes a disordered coil. However, on heating the sample with cations present, the non-aggregated helices melt out first and the aggregated helices melt out at a higher temperature in a second transition.
Corneal contact time of formulations based on gellan gum has been investigated using two main methods, which are fluorometry 44 and -scintigraphy. Gelrite has also provided corneal residence times superior to those of other hydrogel preparations based on polymers such as cellulosic derivatives or xanthan gum.
Alginates being a family of unbranched binary copolymers, alginates consist of 14 linked -D-mannuronic acid M and -L-guluronic acid G residues of widely varying composition and sequence. By partial acid hydrolysis, alginate was separated into three fractions. It was concluded that alginate could be regarded as a true block copolymer composed of homo polymeric regions of M and G, termed M and G-blocks, respectively, inter spaced with regions of alternating structure.
It was further shown that alginates have no regular repeating unit and that the distribution of the monomers along the polymer chain could not be described by bernoullian statistics. Knowledge of the monomeric composition is hence not sufficient to determine the sequential structure of alginates. The aim of this study is to prepare in situ ophthalmic gel of anti-infective drug Levofloxacin hemihydrate to enhance ocular bioavailability and reduce dose frequency and there by increasing patient compliance.
But these preparations when instilled in to the cul-de sac are rapidly drained away from the ocular cavity due to the tear flow and naso-lachrymal drainage. Only small amount is available for its therapeutic effect resulting in frequent dosing. When a drug solution as dropped in to the eye, effective tear drainage and blinking results in fold reduction of drug concentration in minutes.
Ocular therapy could be significantly improved if the pre-corneal residence time of drugs could be increased, several new preparations have been developed for ophthalmic use not only prolong the contact time of the vehicle at ocular surface, but also to slow down the elimination of the drugs. This problem can be overcome by using in situ gel forming ophthalmic drug delivery systems prepared from polymers that exhibit reversible phase transition and pseudoplastic behavior to minimize interference with blinking.
Such system can be formulated as liquid dosage form suitable for administration by instillation in to the eye, which upon exposure to the eye shift to the gel phase; gelation depends upon physiological pH, temperature and ionic strength. To evaluate the prepared formulation for its In vitro gelation and rheological studies, Drug content uniformity, In vitro release studies, Sterility testing of the optimized in situ gel, Stability studies, Pharmacodynamic studies and Pharmacokinetic release studies.
To provide a formulation with better residence time enhanced bioavailability after topical administration and improved patient compliance. Literature survey. Experimental work. Preformulation studies. Interaction studies of polymers and drug before selection of the formulation by FTIR. Formulation of in situ gel by incorporating optimum polymer, excipents and drug. Optimization of ion exchange triggered in situ gelling system using different polymeric concentrations of gelrite.
Estimation of drug by spectrophotometric method. Evaluation studies of prepared in situ gel formulation for rheological properties, in vitro release of the drug, antibacterial studies, sterility, stability studies and pharmacodynamic studies irritation study. Comparative evaluation of in vitro drug release with marketed product. Poly acrylic acid Carbopol was used as the gelling agent in combination of Hydroxy Propyl methylcellulose, which acted as a viscosity-enhancing agent. Gellan gum Gelrite is an anionic exocellular polysaccharide produced by the bacterium pseudo monas elodea, having the characteristic property cation-induced gelation 0.
The developed system is thus a viable alternative to conventional eye drops. Chrystele Le Bourlais et al 6. Despite the excellent acceptance by patients, one of the major problems encountered is rapid precorneal drug loss. To improve ocular drug bioavailability, in situ activated gel forming systems are preferred as they can be delivered as drops, with sustained release properties.
They found that the degree of enhancement of mitotic response following sustained release of Pilocarpine from 1. Srividya B et al They observed that the developed formulation was therapeutically efficacious, stable, non-irritating and provided sustained release of the drug over an 8 h period. Kumar S et al They also studied the rheological characterization of such a system at two different pH 4 and 7 and temperatures 25 and 37C. Thilek kumar M et al They observed that the carbopol solutions which are acidic and less viscous, transform into stiff gels upon increase in pH by tear fluid of the eye and produced sustained release of Indomethacin over 8 hour periods, which made them an excellent candidate for in situ gelling ocular delivery system.
Doijad RC et al Rozier et al They were observed that the formation of the gel prolonged precorneal residence time and increased ocular bioavailability of Timolol. Katarina Lindell et al They were found that in combination both HPMC and carbopol form low viscosity liquid at pH 4 and transform into stiff gels with plastic rheological behaviour and comparable viscosities upon increasing the pH up to 7.
Smadar Cohen et al Shulin Ding et al Recent research efforts in ophthalmic drug delivery have focused on systems in which drug may be administered in the form of eye drops. As a result of these efforts, significant advancements have made in the in situ forming gels. Dimitrova et al They showed that both Pluronics acted very similarly and were more effective as solublizers, created an appropriate viscosity and formed reversible gels at higher temperature, ensured the Indomethacin chemical stability and prolonged in vitro drug diffusion, and showed high physiological tolerance on rabbit eyes.
Odile Sechoy et al They observed that the alginic acid vehicle is an excellent drug carrier, well tolerated and could be used for the development of a long acting ophthalmic formulation of Carteolol. In vitro studies indicated that Carteolol was released slowly from alginic acid formulation, suggesting an ionic interaction. El-Kamel AH et al In vivo study showed that the ocular bioavailability of Timolol maleate increased by 2. Sultana Y et al It was found that the optimum concentration of carbopol solution for in situ gel forming delivery system was 0.
The mixture of solutions showed a significant enhancement in gel strength in the physiological condition. They observed that both in vitro and in vivo studies and these studies indicated that the carbopol and methyl cellulose solution alone and mixture can be used as an in situ gelling vehicle to enhance the ocular bioavailability of Pefloxacin mesylate. Kulkarni M. C et al The formulation in gel form showed almost complete release of drug. The formulation when subjected for accelerated stability studies showed good physical and chemical stability and the in vivo studies of the formulation in albino rabbits confirmed its in situ gelling capacity, non irritancy to eyes as well as its non toxic nature.
Kugalur Ganesan Parthiban et al Benzalkonium chloride at suitable concentration was used as a preservative. Under rheological investigation both solution and gel was found to be having pseudo plastic behaviour. The selected formulations showed sustained release over a period of 8hrs with increased residence times.
Eye irritation test using the Draize test protocol with cross over studies were preformed on selected formulations. Shivanand swamy PH et al The results showed sustained release of Linezolid up to 6 hours. Kaur IP et al Formulations were evaluated for their in vitro release pattern. The effect of these formulations on the intra ocular pressure in rabbits was investigated. These formulations were found to maximize the therapeutic effects with decreased frequency of administration.
Divyesh HS et al Sindhu Abraham et al The formulations were evaluated for clarity, pH, gelling capacity, drug content, rheological study, in vitro drug release, ocular irritancy studies as per Draize test and in vivo corneal permeation studies using isolated goats cornea. The developed formulations showed sustained release of drug up to 6 hrs. The formulations were found to be non irritating with no ocular damage. Johan Carlfors et al He concluded that the elastic moduli of the gels increased with increasing concentration of electrolytes.
At physiological concentration of the electrolytes, the elasticity of the gels was independent of Gelrite concentration. The human contact times increased up to 20 hours with decreasing osmolality of the formulations. Coquelet C et al The interaction between benzalkonium chloride and the respective polymers, the related availability benzalkonium chloride in the corresponding solutions, were studied for aqueous preparation of hydroxy ethyl cellulose, polyvinyl alcohol and cross linked poly acrylic acid.
The study was performed by means of a cross flow filtration process with an alumina membrane. In the presence of the poly acrylic acid gel, the rejection rate of benzalkonium chloride is much higher than with hydroxy ethyl cellulose and polyvinyl alcohol. These results can be explained by the association of the benzalkonium cation with the negative carbohydrate group of the poly acrylic acid.
Furrer et al An ocular irritation test using confocal laser scanning ophthalmoscopy has been developed in which corneal lesions subsequent to instillation of surfactants are specifically marked by fluorescein and assessed by digital image processing. Benzalkonium chloride, a cationic surfactant at a concentration range of 0. The cornea was evaluated for in vivo ocular tolerance by confocal microscopy. In both animal models, the ocular damage increased with the concentration of benzalkonium.
The test was sensitive enough to detect ocular micro lesions at concentration of surfactants as low as 0. Nomenclature : - - S fluoro-2,3-dihydromethyl 4-methyl- 1piperazinyl 7-oxo7Hpyrido [1, 2, 3-de]-1, 4benzoxazinecarboxylicacid hemihydrate.
Molecular Weight : Melting Range : C. Half life : 6 to 8 hours. Appearance Levofloxacin hemihydrate is pale yellow coloured amorphous solid. Solubility Levofloxacin hemihydrate is in soluble in water but its predicted water solubility is 1. It is considered to be freely soluble in this pH range, as defined by USP nomenclature. Above pH 5. Above pH 6. Levofloxacin, like other fluoroquinolones, inhibits the A subunits of DNA gyrase, two subunits encoded by the gyrA gene. This results in strand breakage on a bacterial chromosome, supercoiling and resealing; DNA replication and transcription are inhibited.
Pharmacokinetics Absorption of Levofloxacin after single or multiple doses of to mg is predictable and the amount of drug absorbed increases proportionately with the dose. There is no clinically significant effect of food on the extent of absorption of Levofloxacin.
Adverse Effects The most frequently reported drug-related adverse reaction was transient. Ocular burning or discomfort. Precautions and Warnings If an allergic reaction to Levofloxacin occurs, discontinue the drug. Serious acute hypersensitivity reactions may require immediate emergency treatment, oxygen and airway management, including incubation should be administered as clinically indicated.
As with other anti-infective, prolonged use may result in overgrowth of non susceptible organisms, including fungi. If super infections occur discontinue use and institute alternative therapy. Levofloxacin should be discontinued at the first appearance of a skin rash or any other sign of hypersensitivity reaction.
Usage and Administrations Topically Levofloxacin as 0. Orally Levofloxacin is also used for the treatment of susceptible infections of skin, lungs, ears, airways, bones, and joints caused by susceptible bacteria. Levofloxacin also is frequently used to treat urinary infections, including those resistant to other antibiotics, as well as prostatitis.
Levofloxacin is effective in treating infectious diarrhoea caused by E. Functional Category : Gelling agent alternative to agar. Synonyms : gellan gum. Chemical composition : Polysaccharide comprising glucuronic acid, Rhamnose and glucose. Physical state : Dry powder. Description : Gelrite is a White to tan coloured solid. Materials to avoid : Strong acids, strong bases. Hazardous polymerization: None. Stability and Reactivity Storage and handling procedures should follow the normal practices recognized as desirable for naturally derived polymeric gelling agents.
The gel strength of the dry powder is retained, even after prolonged storage at 50 C 0 F and will recover from freezing. From the results of eye irritation tests, Gelrite is not considered to be an eye irritant. During dust inhalation tests, no toxic symptoms were exhibited by rats exposed to concentrations averaging 6. The lungs of these necropsied rats appeared normal.
Mutagenicity tests show Gelrite to be negative in the Ames test. No special precautions are required to handle Gelrite other studies on the safety of gellan gum are in progress. Applications in Pharmaceutical Formulation or Technology As an in situ ion exchange and thermo reversible gelling agent.
Synonyms : Methyl glycol. Boiling point : C. Density : 1. Flammability : Upper limit Flash point : 99C open cup. Heat of combustion : Melting point : 59C. Refractive index : 1. Description Propylene glycol is a clear, colourless, viscous, and practically odourless Liquid, with a sweet, slightly acrid taste resembling that of glycerine. Functional Category Anti microbial preservative, co solvent, disinfectant, humectant, plasticizer, stabilizing agent. Stability and Storage Conditions At cool temperatures, propylene glycol is stable in a well closed container, but at high temperatures, it tends to oxidize, giving rise to products such as propionaldehyde, lactic acid, pyruvic acid and acetic acid.
Synonyms : Benzalkonii chloridum. Description Benzalkonium chloride occurs as a white or yellowish-white amorphous powder, a thick gel, or gelatinous flakes. It is hygroscopic, soapy to the touch and has a mild aromatic odour and very bitter taste. The average molecular weight of benzalkonium chloride is Functional Category Antimicrobial preservative, antiseptic, disinfectant, solubilising agent and can also be used as wetting agent.
No Instrument Manufacturer 1. U V visible spectrophotometer Shimadzu UV 2. FTIR spectrophotometer Shimadzu 3. Magnetic stirrer Remi motors, Ahmadabad. Mechanical stirrer Remi motors, Ahmadabad 5. Electronic balance Sartorius 6. Digital pH meter Digisun, Hyderabad 7. Stabality chamber Neutronics 9.
Franz diffusion cell Molded 4. It can be defined as an investigation of physical and chemical properties of a drug substance alone and when combined with excipients. The overall objective of preformulation testing is to generate information useful to the formulator in developing stable and bioavailable dosage forms, which can be mass produced.
Melting point determination Melting point of LEV was determined by open capillary method. Solubility Solubility of LEV was determined based on co solvency method using propylene glycol, glycerin and water. The solution was scanned in the range of nm. Table 4. The prepared in situ gels were filled in glass vials closed with rubber closures and sealed with aluminium caps and sterilized by autoclave at 0 C 15 psi for 20 minutes. Interaction studies 72 IR spectra were taken by using Fourier transform infrared spectrophotometer , Shimadzu, Japan.
The pellets of drug and potassium bromide were prepared by compressing the powders at 20 psi on KBrpress and the spectra was scanned in the wave number range of cm. FTIR study was carried on pure drug, physical mixture of drug and polymers, formulations to confirm the compatibility of drug with other excipients used in the preparation of in situ gels Fig.
Visual Appearance and Clarity 33 Visual appearance and clarity was checked under fluorescent light against a white and black back ground for presence of any particulate matter Table 5. Gelling capacity was determined by mixing the formulation with simulated tear fluid in the proportion and examined visually. The composition of simulated tear fluid was sodium chloride 0.
Physiological pH 7. Rheological Studies 73 Viscosity of the instilled formulation is an important factor in determining residence time of drug in the eye. The prepared solutions were allowed to gel in the simulated tear fluid and then the viscosity determination were carried out by using Brooke field viscometer RVT model in spindle no S, angular velocity ran from rpm. The hierarchy of shear rate was reversed and average of two readings was used to calculate viscosity Tables 5.
Sterility Testing 74 Sterility testing is intended for detecting the presence of viable form of microorganisms and was performed for aerobic and anaerobic bacteria and fungi by using fluid thioglycolate medium and soyabean casein digest medium, respectively as per the indian pharmacopoeia. Then it was sterilized by autoclaving at 15 lbs pressure, 0 C for 15 minutes and cooled. After cooling 25 ml of both the medium were transferred to the test tubes. Preparation of Samples The sterile formulations were taken into laminar airflow.
Sterile formulation was removed from the vials by help of syringe. This solution was passed through the membrane filter of 0. After filtration, the filter paper was removed from funnel and it was cut into two half. One half was dropped in bacterial media Fluid thioglycolate and the other half was dropped in the fungal media Soyabean casein digest.
The media were kept for incubation for 7 days at 37 0 C. Both the media were observed every day for any microbial contamination and compared with a positive and negative control Table 5. Drug Content Analysis 62 Estimation of Levofloxacin hemihydrate by Spectrophotometric Method A simple and rapid method for estimation of Levofloxacin hemihydrate by UV spectrophotometric method was developed in simulated tear fluid STF.
Levofloxacin hemihydrate in simulated tear fluid of pH 7. Preparation of simulated tear fluid Dissolve 0. The obtained data is given in Table 5. The vials containing formulation were properly shaken for min. One ml of the formulation was transferred into ml volumetric flask with 1 ml calibrated graduated pipette, 50 ml of simulated tear fluid with pH 7.
Final volume was adjusted to ml with STF, aliquot of 1ml was taken and further diluted to 10 ml with STF, obtained solution was filtered through 0. I n vitro release studies 75 In vitro drug release from the formulations was studied by the diffusion cell. Here the pH of the Lacrimal fluid and the blinking rate of the eye were taken into consideration and were simulated. The procedure for standard calibration is same as mentioned under drug content determination.
The diffusion medium was ml of simulated tear fluid stirred at 50rpm at 37 0 C 0. One end of the diffusion tube was covered by a cellophane membrane. The 1ml formulation were spread on the cellophane membrane and membrane was placed such that it just touches the diffusion medium STF present in receptor compartment.
The drug samples were withdrawn at the interval of one hour for the period of 8 hrs from diffusion medium and analyzed by a UV spectrophotometer at Comparative evaluation of marketed products with prepared in situ gels 75 In vitro release studies of marketed formulation was carried out using bichambered donor receiver compartment model Franz diffusion cell using cellophane membrane soaked overnight in the receptor medium simulated tear fluid, pH 7. Table 5. Staphylococcus aureus, Pseudomonas aeruginosa and E.
Anti microbial efficiency was determined by agar diffusion test employing Cup-Plate method. Sterile solutions of Levofloxacin hemihydrate standard solution and the developed formulations were diluted at different concentration test solutions these solutions were poured in to cups bored into sterile nutrient agar previously seeded with test organisms Pseudomonas aeruginosa, E. The zone of inhibition ZOI measured around each cup and was compared with that of control. The entire operation except the incubation was carried out in a laminar airflow unit.
Both positive and negative controls were maintained during the study Table 5. Ocular Irritancy Studies 77, 78 In developing a novel ophthalmic delivery system, an injury to the eye was taken into consideration. Since, eye being a sensitive, most delicate and yet most valuable of the sense organs, the injuries to the cornea, conjunctiva and iris were measured according to Draize test.
According to the Draize test, the amount of substance applied to the eye is normally l placed into the lower cul-de-sac with observation of the various criteria made at a designed time interval of 1hr, 24hrs, 48hrs, 72hrs and 1week after administration.
Three male rabbits weighing 1. The sterile formulation was instilled twice a day for a period of 7 days and a cross-over study was carried out A 3 day washing period with saline was carried out before the cross-over study. Rabbits were observed periodically for redness, swelling, watering of the eye. Accelerated Stability Studies 1 Stability is defined as the extent, to which a product retains with in specified limits and through out its period of storage and use ie, shelf life.
Stability studies were carried out on optimized formulations according to international conference on harmonization ICH guidelines. The desiccators were placed in a hot air oven maintained at a temperature 40 0 C0. Samples were withdrawn at 7 days interval for 42 Days. Percent drug remaining was calculated and plotted against time in days Tables 5.
Solubility study Solubility of Levofloxacin hemihydrate was found to be dependent on pH. LEV was soluble in co solvent mixture of propylene glycol and water, Glycerin and water, it was also found soluble in organic solvents like DMSO.
Determination of max max of LEV was found to be For confirmation of stability of drug in the prepared formulations the IR spectra was taken and compared with that of pure drug. The result of these studies revealed that there were no definite changes obtained in the bands of drug with respect to pure drug.
These formulations were transparent and clear. The pH of the formulations was found to be 7. All the formulations gave satisfactory results Table 5. Rheological Studies For the development of optimum in situ gelling system, two major prerequisites viscosity and gelling capacity should be taken in consideration, since the ocular shear rate is very high ranging from 0. After 7 days of incubation the results showed no microbial growth in all formulations Table 5.
Estimation of Levofloxacin hemihydrate by Spectrophotometric method A simple Spectrophotometric method for estimation of Levofloxacin hemihydrate was developed in Simulated Tear Fluid, which exhibited max at Results are shown in Table 5. I n vitro release studies The in vitro release of Levofloxacin hemihydrate from the prepared formulations was studied through cellophane membrane using diffusion cell. The release studies of prepared in situ gelling systems were carried out up to 8 hours.
In vitro release studies of marketed eye drops Levobact was done through cellophane membrane using diffusion cell and the release marketed product was up to 3 hours Table 5. Clear zones of inhibition were obtained in all the formulations. The diameter of zone of inhibition produced by formulations against all test microorganisms is given in Table 5. A total four albino rabbits male weighing 1. The sterile formulations were instilled twice a day for a period of 7 days.
The evaluation was made according to the Draize test protocol. All the formulations were found to be non-irritating with no ocular damage or abnormal clinical signs to the cornea, iris, and conjunctiva. Accelerated Stability Studies According to ICH guideline, the accelerated stability studies were carried for prepared in situ gelling systems.
All the Formulations were analyzed for visual appearance, clarity, pH and drug remaining. All the formulations showed slight changes in pH, but it were in acceptable limits 0. Tables 5. Conventional ophthalmic solution dosage forms have advantage such as, ease of instillation and proper dosage administration. Beside ophthalmic ointments have the advantages of increased contact time.
By utilizing these advantages of different dosage forms the newer approach, in situ gelling system was developed. These gels exhibit a unique property of sol-to-gel transition when a change in their physicochemical property takes places. This type of novel ocular drug delivery can provide increased bioavailability by increasing residence time of gel formed and better patient compliance due to ease of administration.
The aim of the present work envisaged Preparation and evaluation of in situ opthalmic gel of an anti infective drug for sustained ocular delivery for the treatment of various bacterial diseases of eye by providing comfortness, compliance to the patients and improved therapeutic performance of the drug over conventional ocular dosage forms. Preparation of in situ gelling Systems In the present work the in situ gelling systems were prepared by ion exchange and temperature dependent methods with the help of gelling agent Gelrite and humectant propylene glycol.
Studies revealed that there was no definite changes in bands were observed with respect to pure drug. So it was confirmed that formulations did not have any drug polymer interactions. Optimized in situ gels were subjected for preliminary evaluation such as visual appearance, clarity, pH and drug content. All formulations were found transparent and clear, pH of the formulations was within 7. Using simulated tear fluid a simple spectrophotometric method for estimation of Levofloxacin hemihydrate was developed.
The absorption maxima by UV spectrophotometer were obtained at During blinking the shear rate on the preparation is large. If the viscosity is too high, this will result in irritation. On the other hand, if the viscosity is too low, it will give rise to increased drainage. So the formulation should have optimum viscosity for easy instillation into the eye as liquid, which will undergo a rapid sol-to-gel transition, hence the good gelling capacity.
But administration of the formulation should influence the pseudoplastic character of precorneal film. It showed that viscosity of all formulations decreased as the shear rate increased, which indicates the character of pseudoplastic fluid. This study showed that formulations did not having any microbial contamination and was sterile.
The in vitro release studies were carried out for all formulations using cellophane membrane and STF as the medium. Release kinetic studies of prepared in situ gels showed that the in situ gels followed first order drug release mechanism.
Higuchi matrix equation confirmed the release by diffusion controlled mechanism. Korsemeyer-Peppas n value of prepared in situ gels was found to be above 0. Obtained results indicated that F6 showed better sustaining effect amongst all formulations. This may be due to the higher concentration of gelrite. Antimicrobial efficacy study carried out by using Staphylococcus Aureus, Pseudomonas Aeruginosa and E. After incubation up to 24 hours, it was found that all formulations were having effective anti microbial action.
Results reveal that no changes were found in visual appearance, clarity and pH. This study showed that there was no definite change observed in the intactness of the drug after accelerated study of 42 days. Hence from the above results we can conclude that it is possible to formulate in situ ophthalmic gels of Levofloxacin hemihydrate using Gelrite for treatment of various bacterial infections.
Optimized formulations F6 0. As per ICH guidelines the stability study of formulations were carried out results showed that formulations were stable transparent and clear at room temperature as well as at 40C. Formulation containing Gelrite 0. FTIR study of physical mixture of drug and polymer, prepared in situ gels was carried out and were compared with IR absorption spectra of pure drug.
Studies reveal that there were no definite changes in bands observed with respect to pure drug. So it was confirmed that formulations do not have any drug polymer interactions. In order to evaluate the rheological behavior, viscosity of the formulations before and after addition of STF was evaluated using Brook Field viscometer. Sterility testing was done by using nutrient agar media and incubated for 7 days under daily observation. This study showed that formulations do not having any microbial contamination and was sterile.
In vitro release of Levofloxacin hemihydrate from the selected formulations was studied through diffusion cell using cellophane membrane for 8 hours. It was compared with the marketed eye drop. Results reveal that all formulations exhibited sustained release of the drug from gelrite polymeric network over 8 hours. Release kinetic studies showed that the in situ gels followed first order drug release mechanism.
Higuchi matrix equation confirmed the release was diffusion controlled. Korsemeyer-Peppas n value of 0. After incubation up to 24 hours, it was found that all formulations had effective anti microbial action. The stability study was carried out for all optimized formulations up to 42 days. Preparation and evaluation of in situ gels for ocular drug delivery. J Pharm Res ;2 6 The complete drug reference, 34th ed. Pharmaceutical press. Ophthalmic drug delivery systems. New York, Marcel Dekker Inc; Chein YW, Novel drug delivery systems, 2nd ed.
Ophthalmic drug delivery systems Recent Advances. Progress in Retinal and Eye Research ;17 1 Pharmaceutical dosage forms: disperse system, 2nd ed. New York, Marcel dekker Inc; vol 2. Hydrogels in pharmaceutical formulations, Eur J Pharm and Biophar ; Ofloxacin ocular inserts: Design, formulation and evaluation. Accordingly, the optimum concentration for Gelrite solution used as in situ gel-forming system was 0.
The viscosity of the polymer solution in the physiological condition can be enhanced significantly by combining the two individual solutions see Fig. This comparative study of the rheological properties of Gelrite and alginate gels has shown that similar gel strengths can be achieved using much lower concentrations of alginate with the added advantage of more viscous sols that would minimize the leakage of preparation from the eye during instillation.
This phenomenon could be explained by the formation of cross-links between the two polymers Therefore, it may be a feasible approach to decrease the amount of alginate required for gelation by incorporating Gelrite in the preparation.
As can be seen from Table I , formulations 3, 4, 12, 15, and 16 had more suitable gelling capacity, which completed the gelation immediately and remained for a few hours, compared with formulations 5 and 17, which also completed the gelation immediately, but remained for an extended period.
However, formulation 13 was accompanied by high viscosity under non-physiological condition; a gel had already formed before administration. Formulation 16 0. The viscosities of polymer solutions at different concentrations were measured at varying shear rates for the relevance of administration by dropping.
The Gelrite solution was shear thinning, and a decrease in viscosity was observed with an increase in shear rate Fig. The rheological behaviors of all formulations were not significantly affected by the addition of matrine. As shown by Fig. Despite the shearing force on the preparation being large during blinking, if the viscosity at high shear rate is too high, it may induce irritation.
But then, if that is too low, it will give rise to increased drainage. The pseudoplastic property of these formulations is in favor of sustaining drainage of drugs from the cul-de-sac of the eye, simultaneously without blinking difficulty. The polymer and ionic contents were varied to examine the effect of dilution upon instillation, and the contributions of electrolytes in the simulated tear fluid to the gel strength were studied.
To change the ionic environment, the required amount of the concentrated salting liquid was added to the preparation under constant stirring until uniform solution was obtained. Between a tear fluid ratio of 0. Thus, at this concentration of Gelrite, there is a sufficient amount of cations present for the immediate formation of a gel in the in vivo case.
At higher ionic contents, e. With increasing salt content, the viscosity of alginate solution is then continuously decreased. These results may suggest that the gel strength was heavily influenced by the salts e. The critical point of tear fluid ratio was defined as the tear fluid ratio when the viscosity of formulation reached the maximum. The viscosity increased at first, and above the critical point of tear fluid ratio, it began to decrease. Furthermore, the untoward effect may be minimized by combining those two individual polymer solutions.
However, there is an experimental error in the determination of viscosity induced by the dilution of concentrated simulated tear fluid; further study is needed to minimize the error. The cumulative amount of matrine released as function of time is shown in Fig. For the eye drops, almost all of the matrine released immediately at the beginning of experiment.
The drug released about In the case of alginate solution, the drug released It obviously exhibited some extent of delayed release effect. There was a Thus, Gelrite solution has a better delayed release effect. The in vitro drug release conditions may be different from those likely to be encountered in the eye.
Cumulative amount of matrine released as a function of time from various matrine-containing solutions. The results from the contact time measurements are given in Table II. The values are averages of at least three measurements. There was no obvious irritation and other serious adverse effects observed. The only untoward effect was a temporary blurring of vision of the eye treated with polymer preparations. The human ocular contact times for Gelrite solutions showed a concentration dependence, indicating that gels were formed with low ion contents.
This could be explained and correlated to the rheology of Gelrite sols mixed with simulated tear fluid. Within the interval studied, the contact time of alginate solutions was also dependent on the concentration and varied among the individuals.
The difference among subjects was probably due to physiological differences such as the lacrimation response and blinking frequency. It was found that the contact time of the polymer solution in the physiological condition could be enhanced significantly by combining the two individual solutions; the maximum contact time obtained is around 1 h.
The trends were consistent in this study and could contribute to the discussion of the rheological results. The results of the ocular irritation studies indicate that all preparations are non-irritant Table III. For all the polymer systems studied, the average irritation scores were zero, including the negative control.
The maximum mean score for ocular lesions observed was 8. Hence, all tested polymer solutions might be considered as minimally irritating to the eye of the rabbits. Excellent ocular tolerance was noted. No ocular damage or abnormal clinical signs to the cornea, iris, or conjunctivae were visible.
A symmetrical peak was observed for matrine with a retention time of 5. There was no interference with the matrine peak, and the overall chromatographic run time was 10 min. The determination of matrine was processed by peak area, and the external standard method was used for quantification. Figure 9 illustrates the matrine concentration in the tear fluid as a function of time. For the individual Gelrite and alginate solution, the matrine concentrations for the alginate formulation were higher than those for the Gelrite formulation between 10 and 60 min of experimental times.
And then matrine concentrations were lower than those for the Gelrite formulation. Therefore, the alginate formulation exhibited a better ability to hold matrine in tear probably due to the mucoadhesive property. For formulations 15 and 16, there was a similar trend between 15 and 60 min at which their matrine concentrations were roughly higher than those of the solutions of Gelrite and alginate.
However, between and min, the matrine concentrations of 15 were slightly higher than those of 16, which had a similar trend to the Gelrite formulation. HPLC chromatogram of standard and tear sample. Matrine concentrations in tears after ocular administration of different matrine-containing solutions.
The AUC of the formulations 15 and 16 were 3. Less pronounced increases in AUC were observed for the Gelrite 2. These results indicated that a greater amount of drug was retained in the precorneal area for a prolonged period following instillation compared to the STF containing matrine. The AUC serves as an indicator of the precorneal exposure to the drug and the therapeutic efficacy of formulation for some drugs.
For the polymer solutions, formulations 15 and 16 had better performance than the formulation with Gelrite and alginate; formulation 16 0. In the present study, we found that the optimum concentrations of Gelrite and alginate solutions for ocular drug delivery system were 0. When 0. Both in vitro and in vivo results indicated that the combined polymer systems performed better in retaining matrine than the individual solutions.
National Center for Biotechnology Information , U. Published online Mar Author information Article notes Copyright and License information Disclaimer. Corresponding author. Received Nov 1; Accepted Mar 2. This article has been cited by other articles in PMC. Abstract The objective of this study was to develop an ion-activated in situ gelling vehicle for ophthalmic delivery of matrine. Methods Preparation of Formulations Gelrite gels of concentrations between 0. Rheological Studies The rheological studies were carried out on a rotating cylinder viscometer Shanghai Precision Instrumentation Co.
In Vitro Release Studies The in vitro release of matrine from the formulations through a 0. In Vivo Studies of Contact Time The contact times of the gels were measured in the eyes of three human volunteers.
Ocular Irritation Studies Ocular irritation studies were performed according to Draize technique on New Zealand White rabbits, each weighing 2. Open in a separate window. Eye Irritation The results of the ocular irritation studies indicate that all preparations are non-irritant Table III.
Formulation Average score Blank of 3 0 3 0 Blank of 12 0 12 0 Blank of 15 0 15 0 Blank of 16 0 16 0 0. References 1. Mechanistic and quantitative evaluation of precorneal pilocarpine disposition in albino rabbits.
J Pharm Sci. Higuchi WI. The analysis of data on the medicament release from ointments. Efficacy and safety of besifloxacin ophthalmic suspension 0. Formulation and evaluation of ciprofloxacin hydrochloride soluble ocular drug insert. Curr Eye Res. Vehicle effects on ocular drug bioavailability. I: Evaluation of fluorometholone. In situ -forming hydrogels for sustained ophthalmic drug delivery.
J Contr Rel. Ganguly S, Dash AK. A novel in situ gel for sustained drug delivery and targeting. Int J Pharm. Effect of Poloxamer gel on the miotic activity of pilocarpine nitrate in rabbits. Ocular therapy with nanoparticulate systems for controlled drug delivery. Ocular delivery of progesterone using a bioadhesive polymer. Gellan-based systems for ophthalmic sustained delivery of methyl prednisolone. Gamma scintigraphic study of precorneal drainage and assessment of miotic response in rabbits of various ophthalmic formulations containing pilocarpine.
Rheological evaluation of Gelrite in situ gels for ophthalmic use. Eur J Pharm Sci. Poly N -isopropylacrylamide -chitosan as thermosensitive in situ gel-forming system for ocular drug delivery. In situ gelling xyloglucan formulations for sustained release ocular delivery of pilocarpine hydrochloride. Controlled release of cephalexin through gellan gum beads: effect of formulation parameters on entrapment efficiency, size, and drug release.
Eur J Pharm Biopharm. In vitro and in vivo evaluation of the Gelrite gellan gum-based ocular delivery system for indomethacin. Acta Pharm. Evaluation of an in situ forming hydrogel wound dressing based on oxidized alginate and gelatin.
Joshi A, Ding S, Himmelstein. Reversible gelation compositions and methods of use. US Patent 5,,, 12 Oct Pongjanyakul T, Puttipipatkhachorn S. Xanthan—alginate composite gel beads: molecular interaction and in vitro characterization.
Yakugaku Zasshi. Yang HF, Zhang F. Research progress of matrine and its preparations. Qilu Pharm Affairs. Ocular anti-inflammatory actions of matrine. J Ocul Pharmacol. Li XT. The pharmacodynamics study of matrine gutta to cure bacterial keratitis and bacterial conjunctivitis. Master thesis, Jilin University; Therapeutic effect of matrine in patients with chronic hepatitis B. Pract Prev Med. Liu JJ.
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The partially dissolved mixture was stored in the refrigerator until the entire polymer was completely dissolved approximately 24 h. Alginate solutions 0. The partially dissolved solutions were then refrigerated until solutions were thoroughly mixed approximately 24 h. The concentrated simulated tear fluid composition: NaCl 6. The rheological studies were carried out on a rotating cylinder viscometer Shanghai Precision Instrumentation Co.
To evaluate the viscosity change after instillation and mixing with the tear fluid, rheological measurements were taken after diluting the formulations with the concentrated simulated tear fluid. The average of two readings was used to calculate the viscosity. All measurements were performed in triplicate. The in vitro release of matrine from the formulations through a 0.
A 1-mL volume of the formulation was accurately pipetted into this equipment; each container was placed in the bottom of a 1,mL beaker. Care was taken to make sure that no air bubbles were inside the polymer solutions. The beaker was then filled with mL dissolution medium and placed in a circulating water bath equipped with stirring rods with paddles to stir the release medium The dissolution medium was freshly prepared simulated tear fluid Aliquots 5 mL were withdrawn at each sampling time and replaced with an equal volume of the release medium.
The release of matrine was analyzed by UV spectrophotometry Shimadzu UV spectrophotometer at nm no interference was observed for matrine with other ingredients under this wavelength. Evaluations were conducted in triplicate. The contact times of the gels were measured in the eyes of three human volunteers.
The experiments were carried out after approval of the protocol by the scientific ethics committee of Chengdu University of Traditional Chinese Medicine. Informed consent was obtained from volunteers for this study. Twenty-five microlitres of the gel was added into the lower conjunctival sac, and the presence of the gel was detected using a slit lamp KJ5D, Kangjie Medical Equipment Company Limited, Suzhou, China. The human subject remained in upright position during the study, and both eyes of the volunteer were treated.
To facilitate the visualization of the gel, all preparations contained fluorescein Ocular inspection was performed at selected time intervals; when only a minute amount or none of the gel remained, it was considered as lost from the eye. The foregoing time for inspection was defined as the contact time of the gel. Ocular irritation studies were performed according to Draize technique on New Zealand White rabbits, each weighing 2.
Fifty microliters of formulation was applied into the left eye of the model rabbit. The right eye, which remained untreated, served as control. To prevent loss of test material, the upper and lower lids were gently held together for approximately 5 s.
The formulations were instilled thrice a day for a period of 10 days, and the rabbits were observed periodically for ocular redness, swelling, and watering. Evaluation was done as per Draize technique Male, New Zealand albino rabbits of 2. During the experiments, the rabbits were placed in restraining boxes where they could move their heads and eyes freely. Kinetic data were obtained from six eyes. The mobile phase consisted of a mixture of methanol and 0.
The flow rate was 1. The two main prerequisites of an in situ gelling system are viscosity and gelling capacity 37 , Aqueous solutions of varying concentrations of Gelrite and alginate were prepared and evaluated for viscosity and gelling capacity in order to identify the compositions suitable for use as in situ gelling systems. The polymer backbone consists of glucose, glucuronic acid, and methyl pentose in the molar ratio Gelrite gels in the presence of monovalent or divalent cations 40 , The mechanism of gelation involves the formation of double-helical junction zones followed by aggregation of double-helical segments to form a 3D network by complexation with cations and hydrogen bonding with water Sodium alginate, the sodium salt of alginic acid, is a natural hydrophilic polysaccharide containing two types of monomers, mannuronic acid M units and guluronic acid G units 43 , Alginate forms stable hydrogels in the presence of certain divalent cations e.
The tear fluid ratio TFR is defined as the quotient, i. The detailed procedure was as follows. The required amount of polymer powder was dispersed in ultrapure water with continuous stirring for 10 min. The partially dissolved polymer solution was stored in the refrigerator until the entire polymer was completely dissolved. Then, the polymer solution was thoroughly mixed with concentrated simulated tear fluid in a ratio of by volume. Thus, junction zones which were due to spontaneous nucleation 46 would not be formed in the gel.
Some measurements were performed in the presence of ions simulating the physiological situation in the eye. As shown in Fig. All of the Gelrite solutions have higher viscosity than that of alginate solutions upon salt uptake. This characterization is advantageous for their proposed usage as the leakage of solution from the eye during instillation would be minimized.
Above the concentration of 0. In addition, other salts e. Effect of concentration on the viscosity of different aqueous polymer solutions without matrine. Solutions tested at 60 rpm. For the high concentration of alginate 1. Hence, the optimum concentration of alginate to be used as the in situ gel-forming agent is 1.
The Gelrite solutions had similar rheological behavior in this 0. Accordingly, the optimum concentration for Gelrite solution used as in situ gel-forming system was 0. The viscosity of the polymer solution in the physiological condition can be enhanced significantly by combining the two individual solutions see Fig. This comparative study of the rheological properties of Gelrite and alginate gels has shown that similar gel strengths can be achieved using much lower concentrations of alginate with the added advantage of more viscous sols that would minimize the leakage of preparation from the eye during instillation.
This phenomenon could be explained by the formation of cross-links between the two polymers Therefore, it may be a feasible approach to decrease the amount of alginate required for gelation by incorporating Gelrite in the preparation. As can be seen from Table I , formulations 3, 4, 12, 15, and 16 had more suitable gelling capacity, which completed the gelation immediately and remained for a few hours, compared with formulations 5 and 17, which also completed the gelation immediately, but remained for an extended period.
However, formulation 13 was accompanied by high viscosity under non-physiological condition; a gel had already formed before administration. Formulation 16 0. The viscosities of polymer solutions at different concentrations were measured at varying shear rates for the relevance of administration by dropping. The Gelrite solution was shear thinning, and a decrease in viscosity was observed with an increase in shear rate Fig.
The rheological behaviors of all formulations were not significantly affected by the addition of matrine. As shown by Fig. Despite the shearing force on the preparation being large during blinking, if the viscosity at high shear rate is too high, it may induce irritation. But then, if that is too low, it will give rise to increased drainage.
The pseudoplastic property of these formulations is in favor of sustaining drainage of drugs from the cul-de-sac of the eye, simultaneously without blinking difficulty. The polymer and ionic contents were varied to examine the effect of dilution upon instillation, and the contributions of electrolytes in the simulated tear fluid to the gel strength were studied. To change the ionic environment, the required amount of the concentrated salting liquid was added to the preparation under constant stirring until uniform solution was obtained.
Between a tear fluid ratio of 0. Thus, at this concentration of Gelrite, there is a sufficient amount of cations present for the immediate formation of a gel in the in vivo case. At higher ionic contents, e. With increasing salt content, the viscosity of alginate solution is then continuously decreased. These results may suggest that the gel strength was heavily influenced by the salts e.
The critical point of tear fluid ratio was defined as the tear fluid ratio when the viscosity of formulation reached the maximum. The viscosity increased at first, and above the critical point of tear fluid ratio, it began to decrease. Furthermore, the untoward effect may be minimized by combining those two individual polymer solutions. However, there is an experimental error in the determination of viscosity induced by the dilution of concentrated simulated tear fluid; further study is needed to minimize the error.
The cumulative amount of matrine released as function of time is shown in Fig. For the eye drops, almost all of the matrine released immediately at the beginning of experiment. The drug released about In the case of alginate solution, the drug released It obviously exhibited some extent of delayed release effect.
There was a Thus, Gelrite solution has a better delayed release effect. The in vitro drug release conditions may be different from those likely to be encountered in the eye. Cumulative amount of matrine released as a function of time from various matrine-containing solutions. The results from the contact time measurements are given in Table II. The values are averages of at least three measurements. There was no obvious irritation and other serious adverse effects observed.
The only untoward effect was a temporary blurring of vision of the eye treated with polymer preparations. The human ocular contact times for Gelrite solutions showed a concentration dependence, indicating that gels were formed with low ion contents.
This could be explained and correlated to the rheology of Gelrite sols mixed with simulated tear fluid. Within the interval studied, the contact time of alginate solutions was also dependent on the concentration and varied among the individuals. The difference among subjects was probably due to physiological differences such as the lacrimation response and blinking frequency. It was found that the contact time of the polymer solution in the physiological condition could be enhanced significantly by combining the two individual solutions; the maximum contact time obtained is around 1 h.
The trends were consistent in this study and could contribute to the discussion of the rheological results. The results of the ocular irritation studies indicate that all preparations are non-irritant Table III. For all the polymer systems studied, the average irritation scores were zero, including the negative control. The maximum mean score for ocular lesions observed was 8.
Hence, all tested polymer solutions might be considered as minimally irritating to the eye of the rabbits. Excellent ocular tolerance was noted. No ocular damage or abnormal clinical signs to the cornea, iris, or conjunctivae were visible. A symmetrical peak was observed for matrine with a retention time of 5.
There was no interference with the matrine peak, and the overall chromatographic run time was 10 min. The determination of matrine was processed by peak area, and the external standard method was used for quantification. Figure 9 illustrates the matrine concentration in the tear fluid as a function of time. For the individual Gelrite and alginate solution, the matrine concentrations for the alginate formulation were higher than those for the Gelrite formulation between 10 and 60 min of experimental times.
And then matrine concentrations were lower than those for the Gelrite formulation. Therefore, the alginate formulation exhibited a better ability to hold matrine in tear probably due to the mucoadhesive property. For formulations 15 and 16, there was a similar trend between 15 and 60 min at which their matrine concentrations were roughly higher than those of the solutions of Gelrite and alginate.
However, between and min, the matrine concentrations of 15 were slightly higher than those of 16, which had a similar trend to the Gelrite formulation. HPLC chromatogram of standard and tear sample. Matrine concentrations in tears after ocular administration of different matrine-containing solutions. The AUC of the formulations 15 and 16 were 3. Less pronounced increases in AUC were observed for the Gelrite 2.
These results indicated that a greater amount of drug was retained in the precorneal area for a prolonged period following instillation compared to the STF containing matrine. The AUC serves as an indicator of the precorneal exposure to the drug and the therapeutic efficacy of formulation for some drugs.
For the polymer solutions, formulations 15 and 16 had better performance than the formulation with Gelrite and alginate; formulation 16 0. In the present study, we found that the optimum concentrations of Gelrite and alginate solutions for ocular drug delivery system were 0. When 0. Both in vitro and in vivo results indicated that the combined polymer systems performed better in retaining matrine than the individual solutions. National Center for Biotechnology Information , U.
Published online Mar These studies reported that microencapsulated tetracaine significantly increased the duration of action and effect of the drugs, compared to standard drug solution. Gelatin is a polymer derived from collagen, a natural constituent of the corneal tissue. Gelatin can interact with the negatively charged mucin layer due to the presence of positively charged amino groups in its structure. Moreover, the presence of arginine-glycine-aspartic acid sequence RGD motif provides cell adhesion properties [ ].
Gelatin NPs have been formulated to successfully deliver timolol [ 76 ] and moxifloxacin [ 77 ] to the corneal surface. Moreover, it has been shown that gelatin NPs possessed good stability, effective lowering of the IOP, high drug bioavailability and lack to irritation [ 76 ].
HA has not only been used as an ingredient for in situ gel forming formulation as described in section 1. For example, HA has been assessed as a coating of chitosan NPs in several studies. HA-coated chitosan NPs demonstrated a higher sustained release of dexamethasone compared to uncoated chitosan NPs, showing that the combination of HA with chitosan results in higher mucoadhesive properties by interacting with hyaluronan receptors on the corneal epithelia [ 78 ].
Moreover, HA-modified chitosan NPs allowed successful delivery of dorzolamide and timolol on an in vivo albino rabbit model. A significantly higher reduction of IOP was observed when compared to a standard drug formulation as well as unmodified chitosan NPs [ 79 ].
Overall, NPs-based systems using natural polymers showed high adhesive properties and good biocompatibility allowing significantly higher drug retention and permeation through ocular tissues without inducing toxicity. However, natural polymers are also known to be easily degraded and their production process are limiting by low batch-to-batch reproducibility [ 4 ].
Compared to natural polymers, synthetic polymers are generally more stable due to lower biodegradability rates, providing a slower and sustained release of drugs. Furthermore, synthetic polymers are more suitable for modifications such that it allows adjustment of their chemical and biological properties, physicochemical state, degradability and mechanical strength, according to the final biomedical applications [ ].
However, synthetic polymers are also considered as less mucoadhesive than natural polymers due to the lack of functional groups that are able to interact with the mucin layer, limiting their bioavailability [ 4 ]. These polymers have been used to successfully deliver a variety of drugs on the ocular surface including anti-inflammatory drugs aceclofenac [ 81 , 82 ], diclofenac [ 83 ] and ibuprofen [ 84 ] , anti-glaucoma drugs betaxolol [ 85 ], acetozalamide [ 86 ], brimonidine [ 87 ] , amphotericin B [ 88 ] and azelastine [ 89 ].
Drug release occurred in a 4-step process, allowing sustained release of betaxolol and thus longer bioavailability. PLA is a hydrophobic polyester synthetized by ring-opening polymerization of lactide. It is FDA-approved and has been widely used for various biomedical applications [ ]. However, the biodegradability rate of PLA is relatively low compared to other polymers [ ], limiting its use for formulation of eye drops; therefore, it is usually grafted with other polymers to tailor its biodegradability [ ].
In a recent study, Liu et al. PBA is a molecule able to form covalent linkage with cis -diol groups of carbohydrates of the mucin layer [ 90 ]. Results showed that the addition of PBA increased the drug retention time without significant toxicity in an in vivo rat model Fig. This polymer has particularly been used to formulate nanocarriers for topical ocular delivery. However, unlike other polymers, PLGA is not mucoadhesive [ 4 ]; therefore, it was combined with polyethylene glycol PEG , a synthetic polymer able to interact with the mucin layer [ ], to formulate mucoadhesive microspheres.
PCL is another synthetic biodegradable polyester, particularly used in tissue engineering and drug delivery systems for varied biomedical applications. PCL has been especially used as nanocarriers for the delivery of carteolol [ ], cyclosporine A [ 95 ] and indomethacin [ 96 ] to the anterior segment. As discussed previously, natural and synthetic polymers present specific advantages and disadvantages for ocular drug delivery.
In order to gather the advantages of each source of polymers, some studies studied the combination of natural and synthetic polymers for the formulation of NPs-based DDS. Synthetic polymers are generally not mucoadhesive, limiting the bioavailability on the corneal surface. In order to overcome this limitation, several formulations of synthetic polymers have been combined with chitosan, which has highly mucoadhesive properties. For example, chitosan was used as a coating for PLGA NPs and showed a sustained delivery of forskalin and thus, a greater IOP lowering effect and duration compared to standard forskalin solution.
Due to its hydrophilic properties, chitosan is not suitable to encapsulate hydrophobic drugs such as amphotericin B. An in vivo ocular pharmacokinetic study showed a prolonged precorneal retention time. Moreover, no sign of irritation was observed during the ocular irritation study [ 99 ]. Chitosan was also combined with PEG to formulate resveratrol-loaded NPs [ ] and resveratrol and quercetin co-encapsulated NPs [ ].
Both studies showed a sustained and enhanced reduction of IOP compared to standard drug solutions. In vivo pharmacokinetics studies showed enhanced precorneal retention time and penetration of the formulated nanosuspensions compared with commercial diclofenac eye drops. This formulation was used to successfully deliver acetazolamide in normotensive rabbits. Results showed a greater IOP decrease and longer duration of the effect was displayed in normotensive rabbits compared with standard acetazolamide solution.
However, no difference was observed for the simultaneous delivery of gatifloxacin and prednisolone, with or without HA coating [ ]. For the past decades, the use of lipidic vectors, such as liposomes or solid-lipid NPs, have widely been used for drug delivery in numerous biomedical applications, especially in ophthalmology.
Due to its hydrophobicity, lipid carriers are suitable for encapsulation of hydrophobic drugs. Moreover, drugs encapsulated into lipophilic carriers can pass the corneal epithelial layer due to the solubilization of the carriers in the lipid cell membranes. However, lipidic formulations are known to be less stable and thus less suitable for sustained drug release.
In recent years, addition of polymers to lipidic NPs formulations have raised special interest in order to increase the stability and mucoadhesiveness of NPs on the corneal surface. So far, chitosan is the polymer that is most combined with liposomes, micelles or solid lipidic NPs. In a study by Ban et al. Interestingly, an in vivo study on rabbit eyes showed an increase of dexamethasone permeation of 2.
These results display the importance of the effect of NP surface charge on the drug release and bioavailability Fig. A Schematic illustration of differently charged lipidic NPs carriers containing dexamethasone From [ ]. More recently, HA has also been combined with lipidic NPs to deliver moxifloxacin [ ], tacrolimus [ ] and doxorubicin [ ]. Due to the ability of HA to target CD44 receptor on the corneal epithelial cells, these studies demonstrated an increase of drug bioavailability without significant toxicity.
Synthetic polymers have also been used to increase the stability and sustained release of drugs delivered by micelles. In particular, diclofenac was loaded in PEG-PCL micelles and showed a 2-fold increase of drug delivery in the aqueous humor of rabbit eyes compared with diclofenac PBS solution eye drops [ ]. As previously described, in situ forming gels and NPs-based systems represent promising strategies for ocular DDS.
In order to combine the efficacy of each of these systems, combination of NPs and in situ gels has been investigated Table 5. Different combinations of NPs and in situ gels were formulated and allowed a successful delivery of a variety of drugs, such as antimicrobial drugs levofloxacin [ , ], vancomycin [ ], fluconazole [ ] , anti-glaucoma drugs brimonidine [ ], curcumin [ ], dexamethasone [ ], epinephrine [ 23 ], timolol [ ] , anti-inflammatory drugs keratolac [ ], pranoprofen [ ] and 5-fluorouracil [ ].
Similar results were obtained for the formulation of levofloxaxin-loaded PLGA NPs combined with chitosan in situ gels. It has been shown that drainage was faster for the marketed formulation, compared with in situ gel, NPs and NPs-gel Fig. A Dynamic gamma scintigraphy study showing percentage radioactivity remaining on cornea with time blue-diamond shape marketed, green triangle shape chitosan in situ gel, red-square shape nanosuspension, purple-circle shape nanoparticle laden in situ gel From [ ].
C The difference of IOP between two eyes i. Also, several studies showed that the combination of NPs and in situ gels can improve drug permeation into ocular tissues and aqueous humor. Chitosan-HA NPs loaded in chitosan in situ gels exhibited a sustained delivery of 5-fluorouracil in rabbit aqueous humor compared to NPs or in situ gels only solution [ ]. Compared to NPs or in situ gels only, their combination allowed to avoid a burst release and sustain the drug delivery to the aqueous humor Fig.
More interestingly, combination of NPs and in situ gels also provides a higher therapeutic effect. Moreover, it has been shown that liposomes loaded in gellan gum in situ gels allowed an increase of the IOP lowering effect and duration of timolol compared with standard eye drops [ ].
Despite the high number of publications describing new ophthalmic DDS, relatively few products are finally commercialized. From bench to batch to market, numerous steps need to be achieved including preclinical and clinical development and pharmacovigilance. Regulations for commercialization of new ophthalmic DDS can vary according to the country. Here, we will describe the regulatory affairs of the three regions where most eye drops are currently commercialized: the United States, Europe and Japan.
Eye drops are defined as medicinal products, if used through pharmaceutical, immunological or metabolic action, or as medical devices if used for cleaning, rinsing or hydrating [ ]. Eye drops containing polymers HA, cellulose derivatives or others such as artificial tears are considered as medical devices because their action is limiting to hydrate the corneal surface. Due to the presence of active pharmaceutical drugs in the formulation, DDS-based eye drops are considered as medicinal products.
To commercialize a new eye drop formulation, pharmaceutical companies must prove the efficacy and safety of their formulations by performing preclinical and clinical studies. One of the most challenging steps for commercialization of new DDS is the production of large-scale batches.
These batches must be produced under Good Manufacturing Practices GMPs , which are guidelines that ensure quality and reproducibility from batch-to-batch. The modification of manufacturing process between academic laboratories and industry can significantly affect the product characteristics and thus, its efficacy and safety [ ].
The Pharmacopeia is a regulatory publication describing all criteria necessary for the manufacturing of medicinal products and the methods of analysis to guarantee quality controls. A complete description of the product must be provided according to the Pharmacopeia of the relevant country, including biological and chemical characterizations, manufacturing process, and quality controls. Biological and chemical criteria include product composition and physicochemical properties appearance, color, pH, osmolarity, drug concentration, stability, sterility and purity.
Stability tests are required to guarantee that the formulation presents the same properties and characteristics within specified limits and throughout its period of storage and use, that it possessed at the time of its manufacturing. Natural materials, such as chitosan or gelatin, are known to be less stable and more degradable than synthetic polymers [ ], explaining the reason for relatively low use of natural materials in ophthalmic formulations.
Maintaining the stability of nano-emulsions and nano-suspensions can also be particularly challenging due to the risk of aggregation and degradation of NPs [ ]. Different techniques of sterilization can be used such as sterile filtration, autoclaving, irradiation or treatment with ethylene oxide and gas plasma. Each of these techniques has advantages and disadvantages that need to be considered according to the properties of the active and inactive ingredients of the formulation.
Moreover, benzalkonium chloride BAK is widely used in multidose eye drops to maintain sterility between uses. However, several studies showed that BAK can have side effects for ocular tissues, resulting in complications such as dry eye, trabecular meshwork degeneration and ocular inflammation [ , ].
An alternative to BAK is the use of single-dose vials or multidose bottles fitted with an antimicrobial membrane. The different Pharmacopeia recommend that endotoxin limits cannot exceed 0. As described previously, natural polymers, such as chitosan or alginate, have particularly interesting properties for use in ophthalmic DDS. However, because they are extracted from natural sources, impurities such as endotoxins could be present and cause immunogenic reactions [ ]. These impurities could explain why chitosan is not used in marketed formulations, despite its numerous advantages for ocular drug delivery.
The goal of preclinical and clinical studies is to assess the efficacy and safety of the formulation from pharmacology, pharmacokinetics and toxicology aspects. In the case of NP-based systems, preliminary in vitro tests are required including drug release, therapeutic activity, mechanism of action, cellular uptake and immunology [ ]. It is usually recommended to perform preclinical studies on two different in vivo animal models, rodent and non-rodent.
Rabbit animal models are the most frequently used for topical ophthalmic drugs and DDS, followed by dog and rat models. In preclinical studies, the formulation is applied on the animal eye and the adapted dosing and side effects are determined. Larger animal models have the advantage of closer anatomical and size proximity to human eyes, but are more expensive, and in the case of some species e. For eye drops, these pharmacokinetic studies are generally performed by quantification of the drug in plasma, tears and other ocular tissues, at different time points after instillation of the eye drop.
Preclinical studies present limitations such as the low number of animals used and the short observation period. Furthermore, the difference in size and shape of ocular tissues, metabolic activity, and blinking rate between animal models and humans may also limit the extrapolation of such data to humans.
Topical medications are the preferred method of drug delivery for numerous ocular disorders, including glaucoma which represents the third cause of blindness, with million cases worldwide [ ]. Despite its ease of use and relatively low cost compared to other treatments, the use of eye drops requires a strict dose regimen.
Moreover, the high albeit highly variable concentrations that can be achieved in ocular tissues can cause side effects that range from relatively minor tolerability issues to significant toxicity side-effects such as the increasingly appreciated toxic effects of anti-glaucoma medications on the ocular surface epithelium.
Poor tolerability profiles are usually associated with poor patient compliance, a major limiting factor for many topical medications. Over the past few decades, a variety of DDS have been marketed for treatment of ocular conditions. In situ gelling systems are cost-effective, easy to produce, and generally biocompatible, making them good candidates for the development of ocular DDS. Beside its advantages, a limited number of in situ gels are currently in clinical use.
In most of the studies detailed herein, significant improved therapeutic effects have been observed using gelling systems. Nevertheless, these improvements are usually not sufficient to significantly reduce the drug dose regimen. Among the marketed formulations containing gelling systems, similar side effects are observed compared with standard formulations.
For these reasons, the development of new types of DDS shows special interests given the numerous published papers on these fields over the last decade. In situ gels have shown their potential to increase the retention time of drugs on the ocular surface, thereby improving their therapeutic effect. Due to the sol-gel transition, the viscosity of in situ forming gels increases upon contact with the eye, limiting drug elimination via nasolacrimal drainage.
Conversely, increase in viscosity can potentially also induce higher lacrimation that can accelerate drug elimination. Moreover, for some stimuli-responsive materials, the gelation efficiency is relatively weak. High concentrations of materials or a combination of several materials have been used that can increase their toxicity.
Highly viscous gels can also induce visual blur, a limiting factor in their use. Compared to in situ forming gels, NP-based systems have shown their ability to increase both drug retention and permeation through ocular tissues with limited increase of the formulation viscosity. Moreover, NP-based systems allow modification of the pharmacokinetics of drug release by prevention of a burst release effect of the drug, particularly of interest in cases of chronic diseases, such as glaucoma. Overall, cationic carriers showed better performance than anionic or non-ionic carriers, due to the electrostatic interactions with the negatively-charged mucin layer of the corneal surface.
NP-based systems have also been incorporated in in situ forming gels and results showed better performance than NPs or gels alone. This trend of combining several DDS suggests that none of these systems alone seems to be efficient enough to achieve a significantly better performance. Despite promising results, the biggest challenge will be to develop these DDS for clinical use. Despite their excellent adhesive and biocompatible properties, the use of natural polymers especially from animal origin in eye drops formulations considerably complicates the production process.
For this reason, problems of stability, sterility and purity need to be anticipated at the very early stage of the product development. Therefore, more research and development need to be done in order to significantly improve methods of preparation and storage guaranteeing efficacy and safety of ocular DDS. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript.
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Corresponding authors: Reza Dana: ude. Copyright notice. The publisher's final edited version of this article is available at J Control Release. See other articles in PMC that cite the published article. Abstract Topical instillation of eye drops remains the most common and for most the easiest route of ocular drug administration, representing the treatment of choice for many ocular diseases.
Keywords: Ocular surface, ocular drug delivery, eye drop, gel, nanoparticle, microparticle. Open in a separate window. In situ gelling systems The use of viscous formulations, such as gels and ointments, have been widely used to increase the retention time of drugs on the ocular surface by limiting the drug elimination via the nasolacrimal drainage. Table 1.
In situ gelling systems used for ophthalmic drug delivery. Measurement of intraocular pressure by indentation tonometer. AUC 0—12h was found 1. Determination of drug concentration of aqueous humor by HPLC. Good biocompatibility and no sign of irritation. AUC 0—min and C max was found 1. No significant difference in the IOP lowering effect was found between in situ gel and standard eye drop.
In situ gel decreased IOP for 24h with a minimum of 8. Standard eye drop decreased IOP for 6—7h with a minimum of 7. Assessment of antimicrobial efficacy by scoring system. No sign of ocular irritation. Determination of drug concentration in ocular tissues by HPLC.
Significant increase of drug concentration levels in corneas AUC 0—min values were found higher for in situ gel compared with standard solution. Precorneal drainage assessment by slit lamps and blue light. Assessment of antiallergic conjunctivitis efficacy by Evans Blue EB extravastion quantification. Residence time was found 2. Extravasted amounts of EB in ocular tissues were found 1. Precorneal retention time by fluorescein staining. Measurement of intraocular pressure by tonometer.
Precorneal retention was around 10 min for standard eye drops and at least 60 min for in situ gel. The maximum IOP lowering effect was observed at 0. The IOP lowering effect lasted 12h and 24h for standard eye drops and in situ gel, respectively.
AUC 0—24h and C max values were found 2. AUC and C max values were found 6. Measurement of intraocular pressure by Schiotz tonometer. AUC 0—9h values were found 1. Bacterial infection study. In situ gel cured corneal infection after 4 days compared to 7 days of photodynamic therapy. After 6h, IOP was found lower for in situ gel Assessment of antimicrobial efficacy on a S. Significant improvement in the observed symptoms for in situ gel compared with marketed solution. Biopermanence PET study No sign of ocular irritation.
Precorneal drainage assessment by gamma scintigraphy. AUC 0—10h values were found 3. Determination of drug concentration in tear fluid by HPLC. AUC 0—30 values were found 4. AUC 0—h values were found 4. Standard eye drop cleared more rapidly from the corneal region and reached systemic circulation via nasolacrimal drainage, compared with in situ gel. At all time points, in situ gels exhibited stronger IOP lowering effect compared with standard solution.
Maximum IOP decrease was found higher for in situ gel 3. Thermo-responsive gelling systems. Xyloglucan-based gelling systems Xyloglucan is a highly soluble natural polysaccharide derived from tamarind seeds. Sustained drug release and improved therapeutic effect by using in situ gels compared with conventional eye drops.
Glycerol phosphate-based gelling systems Recently, glycerol phosphate has been used to modify the thermo-responsive properties of natural polymers, including chitosan and gelatin. Chitosan-based gelling systems Chitosan is a linear amino polysaccharide derived from chitin, the main component of shells of crustaceans, insects and microorganisms, representing the second most abundant natural polymer on earth after cellulose.
Alginate-based in situ gelling systems Alginate is a natural, anionic, hydrophilic polysaccharide isolated from brown seaweed. Multi-stimuli responsive gelling systems In order to increase strength and gelation properties of gelling systems, combinations of different stimuli-responsive materials have been tested. Nanoparticle-based drug delivery systems One of the reasons for the low bioavailability of drugs after topical administration is the short retention time due to the rapid clearance of the ocular surface via tear film renewal, nasolacrimal drainage and biologic and enzymatic drug degradation.
Table 2. Nanoparticles-based systems used for ophthalmic drug delivery. Determination of drug concentration in aqueous humor by HPLC. AUC 0—min values were found to be 2. C max was found to be similar for NPs solution and commercial eye drops. After 2h, drug concentration was found to be After 72h, drug concentration was found to be Corneal and conjunctival drug levels were found 2- fold to 6-fold higher for NPs solution compared with standard aqueous solution.
AUC and C max values were found fold and fold higher, respectively, for NPs solution compared with standard solution. Measurement of intraocular pressure. After 1. Maximal IOP lowering effect was observed at 4h with a value of Maximal IOP lowering effect was observed at 3h with a value of 6. Measurement of intraocular pressure by a Schiotz tonometer. Standard solution showed a quick fall in radioactive counts on corneal surface with respect of time as compared to NPs suspension in 0.
Maximum IOP lowering effect was observed at 2h with a value of Maximum IOP lowering effect was observed at 1h with a value of AUC 0—8 and C max values were found fold and fold higher, respectively, for NPs solution compared with standard solution.
AUC values were found to be 3. No statistical difference of efficacy between NPs solution and standard solution. Duration of action was 4-fold higher for NPs solution compared with standard solution. AUC values were found to be at Maximum effect pupil-corneal ratio was found to be at 0. Measurement of intraocular pressure by a plunger load tonometer. AUC values were found to be 2. Assessment of antimicrobial efficacy by observation of clinical parameters.
IOP lowering effect peaked at 3h for marketed solution, at 4h and observed for up to 8h for chitosan NPs solution, and at 4h and observed for up to 12 h for chitosan-HA NPs solution. Maximum IOP reduction was found 1. PMN count in tears were found to be 1. PMN count in tears at 3h were found to be 1. Greater decrease of PMN count at all time points for NPs solution compared with standard aqueous solution.
Measurement of intraocular pressure by an indentation tonometer. NPs solution was found safer and less toxic than standard solution. Higher drug concentrations were found at all time points for NPs solution compared with standard solution. After 90 min, drug concentrations cannot be detected for standard solution, whereas drug concentrations were detected until min for NPs solution. For standard solution, maximum IOP lowering effect was found at 30 min 5.
After 6h, no IOP lowering effect was observed. Histopathology analysis. No sign of ocular toxicity. Assessment of anti-inflammatory efficacy by scoring of clinical symptoms. PMN counts were found significantly lower for MPs solution, compared with standard aqueous solution.
AUC values were significantly higher for NPs solution compared with oily control. Assessment of precorneal retention by gamma scintigraphy. Precorneal retention was found significantly higher for NPs solution compared with standard solution. For standard solution, maximum IOP lowering effect was found at 1h Assessment of corneal permeation by fluorescein staining.
AUC values were found 1. Higher permeation and retention effects were noted for NPs solution compared with fluorescein solution. Measurement of intraocular pressure by a tonometer. Assessment of corneal permeation by Nile red staining. AUC 0—24h and C max values were found 1. AUC 0—8h values were AUC 0—24h and C max values were found 5. Higher precorneal retention of chitosan-coated liposomes compared with standard eye drops and liposomes.
Maximum IOP was Determination of drug concentration in tear fluid and aqueous humor by HPLC. Chitosan-lipid carriers had a significantly greater percentage activity remaining in the pre-corneal area after 30 min Determination of drug concentration in tear fluid by mass spectrophotometry. AUC 0—10min values for chitosan-coated liposomes were found to be 2.
AUC 0—10min values for chitosan-coated lipid carriers were found 4. Assessment of precorneal retention by fluorescein staining. Assessment of anti-microbial efficacy by keratitis induction and symptoms scoring. Precorneal retention time was observed during 40—60 min for chitosan lipid carriers and for 20—40 min for lipid carriers. Maximum drug concentration was found at 1h for commercial eye drops and at 4h for chitosan lipid carrier.
After keratitis induction, significantly lower conjunctival redness and corneal opacity was observed with chitosan lipid nanocarrier treatment compared with commercial solution. Clearance was significantly decreased 7. Higher drug absorptions in cornea, conjunctiva and sclera for chitosan-coated liposomes compared with liposomes. The relative bioavailability of HA-coated niosomes was 2.
Assessment of drug permeation in cornea by laser scanning microscopy. AUC and C max values were found 1. Higher drug permeation was noted for NPs solution compared with standard solution. NPs solution exhibited 4. Polymeric nanoparticles Due to recent advances in the fields of biomaterials and nanotechnology, new types of polymeric DDS have been developed.
Naturally derived polymer-based nanoparticles Natural polymers are generally considered more biocompatible and mucoadhesive compared to synthetic polymers, making them suitable for the formulation of NPs for ocular DDS. Hyaluronic acid. Synthetic derived polymer-based nanoparticles Compared to natural polymers, synthetic polymers are generally more stable due to lower biodegradability rates, providing a slower and sustained release of drugs.
Poly lactic acid PLA. Increased drug retention by using poly lactic acid PLA -based nanoparticle systems. Poly lactic-co-glycolic acid PLGA. Polycaprolactone PCL. Combination of natural and synthetic polymers As discussed previously, natural and synthetic polymers present specific advantages and disadvantages for ocular drug delivery. Chitosan-based combinations. Increased corneal retention and sustained release of drugs by combining in situ gels and NPs.
Challenges for the commercial development of new ophthalmic drug delivery systems Despite the high number of publications describing new ophthalmic DDS, relatively few products are finally commercialized. Regulatory affairs Eye drops are defined as medicinal products, if used through pharmaceutical, immunological or metabolic action, or as medical devices if used for cleaning, rinsing or hydrating [ ].
Production process and quality controls One of the most challenging steps for commercialization of new DDS is the production of large-scale batches. Particle size. Preclinical and clinical studies The goal of preclinical and clinical studies is to assess the efficacy and safety of the formulation from pharmacology, pharmacokinetics and toxicology aspects.
Concluding perspectives Topical medications are the preferred method of drug delivery for numerous ocular disorders, including glaucoma which represents the third cause of blindness, with million cases worldwide [ ]. Drug delivery systems combining nanoparticles and in situ forming gels. NPs-gel retained for longer duration at corneal surface and negligible radioactivity was observed in other organs compared with aqueous solution.
AUC 0—8h was found 3. In situ gel achieved a C max of approximatively 0. NPs-gel had a plateau 0. Faster decline in radioactivity counts on the corneal surface for marketed formulation, compared with in situ gel, NPs and NPs-gel. C max was found to be 5. AUC 0—12h was found 2. C max was found to be 1. No sign of ocular irritation and no abnormal winking compared with simulated tear fluid. AUC 0—8h was found to be 2.
Anti-inflammatory efficacy assessment by inflammation symptom scoring. Determination of drug concentration in external ocular tissues by the disc diffusion. AUC 0. C max was found 8. In situ gel decreased IOP for at least 32h with a minimum of 6. Standard eye drop decreased IOP for 6h with a minimum of 4. Measurement of intraocular pressure by invagination tonometer. Liposomes-gel decreased IOP from 30— min and a minimum of Standard eye drops decreased IOP from 30—min, with a minimum of Footnotes Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication.
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