Chemical, dissolution stability and microscopic evaluation of suspensions of ibuprofen and sustained release ibuprofen-wax microspheres

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Abstract
Chemical stability studies of suspensions of ibuprofen powder and ibuprofen-wax microspheres were performed using an accelerated stability protocol with a modified high performance liquid chromatography (HPLC) procedure. The variables considered were pH, suspending agents and temperature. The study showed little or no chemical degradation in the different suspending agents after storage for three months. Dissolution stability was examined in suspensions of ibuprofen microspheres made from an optimized formulation with 17% drug loading. The storage temperature were 23, 37 and 45 degrees C. Other variables for the dissolution stability studies were suspending agents, wax types, suspending medium pH and microsphere size. Suspensions of ceresine wax microspheres stored at 37 degrees C showed faster drug release than room temperature storage, but suspensions stored at 45 degrees C showed an opposite effect. Microspheres suspended in syrup and stored at 37 degrees C had faster dissolution rates than microspheres suspended in methylcellulose at the same temperature, possibly as a result of an interaction between the syrup and the microsphere constituents. Suspensions of microcrystalline wax microspheres had better dissolution stability than microspheres made from ceresine wax. Higher suspending medium pH resulted in faster release of drug from the suspended microspheres, but particle size did not significantly affect the dissolution stability.