An in vitro method of evaluating tolnaftate release from topical powder

A dissolution apparatus was constructed to evaluate tolnaftate release from topical powders. It consisted of a mesh unit to support the powder, a receptor phase, and a sink. This report describes three parameters that were used to evaluate this technique. First, three different areas of contact were examined using 52-, 41-, or 30-µm mesh supports. Second, the effect of the pH on the dissolution rate was studied, using aqueous buffers of pH 3, 5, 7, or 8 as the receptor phase. Finally, different topical powder formulations containing different amounts of tolnaftate were tested. The results obtained showed that the percentage of tolnaftate released from topical powders increased at low pH levels and with the larger mesh support. The percentage released was greater in a starch-talc preparation than in a talc-only preparation. The mesh was replaced by a semipermeable membrane (2.5- to 4 nm pore size) to function as an in vitro model for intradermal diffusion. The results showed that a cream initially released more drug than powder formulations.