Comparison of the Hanson Microette (R) and the Van Kel apparatus for in vitro release testing of topical semisolid formulations

Purpose. The major goal of this study was to compare the relative utility o f the Hanson Microette(R) and the Van Kel apparatus, two fully automated de vices, as in vitro release tests (IVRT) for semisolids. We attempted to dev elop methodology that can be used to discriminate formulation changes, and to evaluate the precision, reproducibility and technical complexity of each test apparatus. Methods. We chose the sunscreen Eusolex(R)232 (2-Phenylbenzimidazole-5-sulf onic acid) as a model compound, which was incorporated into an emulsion for mulation prepared in our laboratory. Test conditions for the two IVRT were made as nearly identical as possible, in order to obtain an accurate compar ison. Results. The formulations were tested and found to be physically stable thr oughout the entire study. Diffusion coefficients were apparatus-dependent b ut were independent of the drug concentration in the formulations. The IVRT data were plotted as amount released (mug/cm(2)) vs. square root of time ( s(0.5)) and a linear relationship was obtained in each case. Both methods p roduced similar results and were able to detect changes in drug loading in the formulations. Conclusions. The linear relationship between the amount released and the sq uare root of time indicates a diffusion-controlled release of drug. Both ap paratuses proved to be suitable as tests for formulation "sameness" accordi ng to the FDA's SUPAC-SS guidelines, during level 3 changes. However, each apparatus produced a different release profile for the drug. The choice of apparatus will depend upon a number of considerations.