Designing of a pH-Triggered Carbopol®/HPMC In Situ Gel for Ocular Delivery of Dorzolamide HCl: In Vitro, In Vivo, and Ex Vivo Evaluation

Dorzolamide HCl (DRZ) ophthalmic drop is one of the most common glaucoma medications which rapidly eliminates after instillation leading to short residence time of the drug on cornea. The purpose of the present study is to develop a pH-triggered in situ gel system for ophthalmic delivery of DRZ for treatment of ocular hypertension. In this study, a 3(2) full factorial design was used for preparation of in situ gel formulations using different levels of Carbopol (R) and hydroxyl propyl methyl cellulose (HPMC). Rheological behavior, in vitro drug release, ex vivo corneal permeability, and IOP-lowering activity were investigated. DRZ solution (2% w/v) containing of 0.1% (w/v) Carbopol (R) and 0.1% (w/v) HPMC was selected as the optimal formulation considering its free flow under non-physiological conditions (initial pH and 25 +/- 2 degrees C) and transition to appropriate gel form under physiological circumstance (pH7.4 and 34 degrees C). This in situ gel presented the mucoadhesive property. Ex vivo corneal permeability of this combined solution was similar to those of DRZ solution. The developed formulation compared to the marketed drop (Biosopt (R)) and DRZ 2% solution had a better performance in intraocular pressure activity. The efficiency and long duration of IOP reduction could be due to the prolonged residence time of the in situ gel. The presence of Carbopol (R) as a pH triggered and mucoadhesive polymer causes to attach to the ocular mucosal surface for a long term.