Development in release testing of topical dosage forms: use of the Enhancer Cell with automated sampling

The aim of this study was to evaluate an automated method using the Enhancer Cell and compare the release of the corticosteroid triamcinolone acetonide (TA) from commercial semisolid formulations. The method used a modified USP Apparatus 2 using the Enhancer Cell in 200 ml capacity flasks instead of the standard 900 ml flasks. The additional equipment included an adapter plate to position the flasks in the center, a cover to reduce the receptor phase evaporation and smaller sized (1/4 in.) shaft and collets. All products were evaluated prior to their expiration date. Effects of system variables such as the temperature and composition of the receptor medium, stirring speed, and the choice of membrane on the drug release were evaluated. Statistical analysis was carried out using SAS Ver. 6.07 and the slopes and intercepts (of the cumulative release/unit area versus square root of time plots) were compared. TA release was a linear function of the square root of time (P < or = 0.0001), in accordance with Higuchi's model (r2 > or = 0.9 in most cases). Temperature (32 and 37 degrees C) did not affect the drug release (P > 0.32) but a significantly higher release rate was observed (P < or = 0.0001) at 50 degrees C. Stirring speed (50, 100, 200 rpm) (P > 0.26) and receptor media composition (38 and 76% ethanol) (P > 0.68) did not significantly alter the release rates. Membrane selection (regenerated cellulose, polyethylene, and rat skin) was found to be a significant variable (P < or = 0.004). This study demonstrates the use of the Enhancer Cell as an automated quality control tool in the in vitro release testing procedure for semisolid drug formulations.