A novel USP apparatus 4 based release testing method for dispersed systems

A novel dialysis adapter has been developed for USP apparatus 4 for in vitro release testing of dispersed system dosage forms. This USP apparatus 4 method was optimized and compared with currently used dialysis and reverse dialysis sac methods. Optimization studies for the USP apparatus 4 method showed that release from solution, suspension and liposome formulations was not flow rate limited and was not affected by change in the dialysis adapter sample volume from 250 μl to 500 μl. The USP apparatus 4 method could discriminate between solution, suspension and liposome formulations of dexamethasone. On comparing the different methods, only the USP apparatus 4 method provided discrimination between dexamethasone release from extruded and non-extruded liposomes, as well as among non-extruded DMPC, DPPC and DSPC liposomes. The dialysis sac method could not discriminate between the release profiles of non-extruded DMPC and DPPC liposomes. The reverse dialysis sac could not discriminate between the release profiles of extruded and non-extruded DMPC liposomes. In addition, the USP apparatus 4 method provided the highest release and the smallest variation in the data. This novel adapter might address the problem of the lack of a compendial apparatus for in vitro release testing of dispersed system dosage forms.