A REVIEW ON TOPICAL OPHTHALMIC DRUG DELIVERY SYSTEMS
Three methods have been employed to cause phase transition in the eye surface. These are change in pH, change in temperature and ion activation. pH: In this method gelling of the solution is triggered by a change in the pH. CAP latex cross linked polyacrylic acid and derivatives such as carbomers are used. They are low viscosity polymeric dispersion in water which undergoes spontaneous coagulation and gelation after instillafion in the conjunctival cul-de-sac19. 3. Temperature: In this method gelling of the solution is triggered by change in the temperature. Sustained drug delivery can be achieved by the use of a polymer that changes from solution to gel at the temperature of the eye. But disadvantage of this is characterized by high polymer concentration (25% Poloxamers)20. Methyl cellulose and smart hydrogels are other examples. 4. Ionic strength: In this method gelling of the solution Instilled Is triggered by change In the Ionic strength. Example Is Gelrite. Gelrite is a polysaccharide, low acetyl gellan gum, which forms a clear gel in the presence of mono or divalent cations. The concentration of sodium in human tears is 2.6 g/l is particularly suitable to cause gelation of the material when topically installed into the conjunctival sac. 5. Oil in water emulsions: Phospholipids and pluronics were used as the emulsifiers. Antioxidants were added to improve their shelf-life. The intra-ocular pressure reducing effect of a single, topically administered dose of a pilocarpine emulsion lasted for 29 h in rabbits compared to generic pilocarpine solution Which lasted only for 5 h21 .Pages: 1 2 3 4 5 [6] 7 8 9 10 11 12 13 14
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20.02.2010
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