Vertical diffusion cells (VDC) have been envisaged as in vitro surrogates for ensuring product quality and performance for topical preparations. USP General Chapter <1724> Semisolid Drug Products-Product Performance Tests describes the application of VDC as one of the apparatus required for in vitro testing of topical products. Knowledge of various operational parameters and their impact on drug release during diffusion experiments thus becomes imperative. In the present study, parameters like temperature, composition of receptor medium, speed of stirring, and filled volume of cell jacket have been evaluated for their influence on drug release rate from hydrocortisone cream employing vertical diffusion cells. The statistical analysis of the results was performed by one-way ANOVA with Bonferroni post hoc test. Results suggest that the composition of the receptor medium significantly influences drug release from cream, and slower stirring rates translate to lower release rates. On the other hand, within experimental design, the temperature of the receptor and filled condition of the cell jacket do not influence drug release significantly.

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Interdiffusion was investigated with solid-solid diffusion couples in the Q (fcc) region of the quaternary Ni-Cr-Co-Mo system at 13OOOC for the determination of diffusion paths and diffusional interactions among the components. The concentration profiles for a given couple exhibited a common cross-over composition, Y,, which reflected the relative depths of diffusion in the terminal alloys. Interdiffusion fluxes were calculated directly from the concentration profiles and the quaternary interdiffusion coefficients were calculated at selected compositions. Ni and Co ex hibited uphill diffusion against their individual concentration gradients in a direction opposite to the interdiffusion of Cr. Quaternary diffusion paths were presented as a set of partial diffusion paths on the basis of relative concentration variables.-_ _~ DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily ,constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.