Effect of Various Operational Parameters on Drug Release from a 1% Hydrocortisone Semisolid Dosage Form Using the Vertical Diffusion Cell Apparatus

The purpose of this study was to identify operational parameters of the vertical diffusion cell (VDC) apparatus that have an influence on results of drug release testing from semisolid dosage forms, which are one of three types of topically applied products (see USP General Chapter Topical and Transdermal Drug Products-Product Quality Tests < 3 >). The VDC apparatus operates using a static diffusion cell, a synthetic membrane, and an appropriate receptor medium. A cream formulation containing 1% hydrocortisone was used for the current study. The operational parameters investigated were stirring rate, mixing helix, stirring while sampling, medium degassing, membrane wetting with Ethomeen (a surfactant), and membrane wetting time. Stat-Ease design of experiment software was used to create partial factorial experimental designs to evaluate these parameters. The effects of the operational parameters were evaluated using mean drug release rate (slope, mu g/cm(2)/min(1/2)) and the standard deviation (SD) of six individual release rates for each experimental setup. Results of the study indicate that one parameter, the presence of Ethomeen for wetting the membrane, had a large and significant effect on both drug release rates and SD. Two parameters, stirring while sampling and mixing helix, had a significant impact on the drug release rate when Ethomeen was not used. Two parameters, medium degassing and stirring while sampling, had significant effects on the variability of the results (SD). Additionally, instrument-specific parameters (e.g., mixing helix) also contributed significantly to the variability of drug release rates.