Formulation of hydrophilic non-aqueous gel: Drug stability in different solvents and rheological behavior of gel matrices

Purpose. This study was aimed at formulating a hydrophilic non-aqueous gel for topical delivery of the model moisture-sensitive drug, minocycline hydrochloride (MH). Methods. Stability study of MH dissolved in water and various hydrophilic non-aqueous solvents was performed over a period of four months in order to select a suitable non-aqueous solvent for MH gel. To improve MH stability, the effect of different cation additives on MH stability in the selected solvent was investigated. Non-aqueous gel matrices were prepared from three different types of hydrophilic polymers in glycerin-propylene glycol mixture with Mg2+ cation additive. Oscillatory shear rheometry was performed on the gel matrices using a cone-and-plate rheometer. Results. MH stability was affected by the type of solvent employed and the duration of storage. Different cation additives affected the extent of MH stabilization through MH-cation complex formation. Rheological properties of the non-aqueous gel matrices were significantly affected by the type and concentration of polymer, and the vehicle ratios in the formulations. Conclusions. MH stabilization could be achieved using the selected glycerin-propylene glycol mixture containing MgCl2. Gel matrix formulated using this solvent system and 3%w/w N-vinylacetamide/sodium acrylate copolymer had demonstrated the most favorable rheological properties as a gel for topical application.