Objective: The goal of this study was to develop and characterize an ion-activated in situ gel-forming brimonidine tartrate, solution eye drops containing xanthan gum as a mucoadhesive polymer.Method: Sol-gel formulation was prepared using gellan gum as an ion-activated gel-forming polymer, xanthan gum as mucoadhesive agent, and hydroxypropyl methyl cellulose (HPMC E50LV) as release retardant polymer. Phenylethyl alcohol is used as preservatives in borate buffer. The 23 factorial design was

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... oyed to optimize the formulation considering the concentration of gelrite, xanthan gum and HPMC as independent variables, gelation time, gel strength, and mucoadhesive force (N). Gelation time , gel strength, mucoadhesive force (N), viscosity (cP) and in vitro percentage drug release were chosen as dependent variables. The formulation was characteristics for pH, clarity, isotonicity, sterility, rheological behavior, and in vitro drug release, ocular irritation, and ocular visualization.Result: Based on desirability index of responses, the formulation containing a concentration of gelrite (0.4%), xanthan gum (0.21%), and HPMC (HPMC E50 (0.24%) was found to be the optimized formulation concentration developed by 23 factorial design. The solution eye drops resulted in an in situ phase change to gel-state when mixed with simulated tear fluid. The gel formation was also confirmed by viscoelastic measurements. Drug release from the gel followed non-fickian mechanism with 88% of drug released in 10 h, thus increased the residence time of the drug.Conclusion: An in situ gelling system is a valuable alternative to the conventional system with added benefits of sustained drug release which may ultimately result in improved patient compliance.