ABSTRACT
The new concept of producing a gel in situ was suggested for the first time in the early 1980s. It is widely accepted that increasing the viscosity of a drug formulation in the precorneal region will lead to an increased bioavailability, due to slower drainage from the cornea. The gelled system constitutes an in situ microreservoir of high viscosity. A pH-triggered ophthalmic latex is a low-viscosity polymeric dispersion in water which undergoes spontaneous coagulation and gelation after instillation in the conjunctival cul-de-sac. The alkali-induced thickening phenomenon of anionic latices was considered most interesting for the concept of an ophthalmic drug delivery system, because of the presence of a carbonic buffer system regulating the pH of tears as described by Ibrahim. Ophthalmic dosage forms have been virtually limited to solutions, ointments, suspensions, and emulsions. One is a typical emulsion polymerization, the other, a dispersion of an already formed polymer in water, called pseudolatex.
