Rationalized Approach for Formulation and Optimization of Ebastine Microemulsion Using Design Expert for Solubility Enhancement

Abstract

Ebastine is available as an oral antihistamine formula for allergic disorders such as tablets and syrup. Oral ebastine causes unfavorable effects on heart like QT prolongation, severe gastric distress, decreased tear production, resulting in dryness of the ocular surface, which exacerbates ocular discomfort and increasing susceptibility of eye to irritation. To avoid systemic side effects and ocular discomfort, topical ocular therapy could prove to be superior to systemic therapy in treating ocular allergies. Hence, topical formulation was developed to achieve onsite exposure of ebastine for ocular allergies. Moreover, conjunctiva is more accessible to hydrophilic molecules than lipophilic molecules. This creates challenge for a lipophilic molecule such as ebastine for topical ocular development. Successful dissolution of ebastine in o/w microemulsion allows its use in more convenient soluble form. Initially, solubility of drug in various oils, surfactant and cosurfactant was determined, followed by pseudo-ternary phase diagram to find microemulsion area. The D-optimal mixture design was employed for optimization of formulation. The optimized microemulsion formulation was characterized for its transparency, drug content, droplet size, zeta potential, viscosity, isotonicity, osmolarity and surface tension etc. The optimum physicochemical properties were observed to be eye-fitting. Carboxy methyl cellulose and sodium hyaluronate were used as gelling agents at different concentrations to increase residential time at the site of action. In vitro drug release study revealed that ebastine release from microemulsion gel in a sustained manner up to 24 hrs. for the purpose of providing prolonged therapy for ocular allergy. Hence, prepared microemulsion had great potential as an alternative to customary oral formulations of poorly soluble drug.