Evaluation of mathematical models describing drug release from estradiol transdermal systems

The in vitro release profiles of 13 patches of estradiol (from five marketed products) were determined by the paddle-over-disk method. The transdermal systems were membrane-controlled type or matrix diffusion-controlled type. The estradiol content of test aliquots of the dissolution medium was determined by HPLC. To analyze the release mechanism, several release models were tested such as zero order, first order, Higuchi, Weibull, Korsmeyer-Peppas, and Makoid-Banakar. The release profiles showed that the drug was released at a constant rate for three patches. The drug-release rate from the other 10 patches was not constant, and diminished with the square-root of time (Higuchi model).