In vitro release kinetics of salicylic acid from hydrogel patch formulations

Hydrogel patch formulations containing 15% and 21% w/w salicylic acid (SA) are commercially available for the treatment of warts. The release of SA from these formulations was monitored by a procedure reported for in vitro evaluation of transdermal dosage forms (Shah et al., Int. J. Pharm., 32 (1986) 243-250). The studies were carried out on 3 formulations. The appropriate number of patches of each formulation were placed on a watch glass and covered with an aluminum wire screen. Phosphate buffer (pH 7.4) maintained at 32°C was the release medium. HPLC analyses of the release medium revealed that complete release of SA from all the formulations occurred in ≤8 h. Plots of the fraction of incorporated drug released (up to the release of ~60% of the incorporated drug) as a function of square root of time were linear indicating matrix diffusion controlled release mechanism. Storage of the packaged formulations under ambient conditions for 9 months caused no change in the rate and extent of SA release. This technique has potential utility as a quality assurance test for these formulations.