The poor bioavailability and therapeutic response exhibited by conventional ophthalmic solutions due to rapid precorneal elimination of the drug may be overcome by the use of in situ gel-forming systems that are instilled as drops into the eye and undergo a sol–gel transition in the cul-de-sac. The present work describes the formulation and evaluation of an ophthalmic delivery system of an antiviral agent, Acyclovir sodium, based on the concept of pH-triggered in situ gelation. Polyacrylic acid (Carbopol® 940) was used as the gelling agent in combination with hydroxypropyl methylcellulose (HPMC) which acts as a viscosity enhancing agent. The developed formulation was therapeutically efficacious, stable and non-irritant and provided controlled release of the drug over an 8 hr period. The developed system is thus a viable alternative to conventional eye drops.
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