Timed release from polymeric films containing drugs and kinetics of drug release

The preparation of cast films of ethylcellulose containing caffeine and salicylic acid is described. These films exhibit timed release of drugs. Release rates were found to agree with both the classical first-order equation (log drug retained against time) and diffusion-controlled release models, as exemplified by Higuchi's equations (drug release linearly related to square root of time). Mathematical analysis of the data shows that the release behavior actually conforms with the diffusion-controlled model. Literature results, reported as first order, for the release of cetylpyridinium chloride and benzalkonium chloride from polyamide films were analyzed similarly and shown to be diffusion controlled. Recommendations are made for presentation and routine treatment of drug release data to avoid ambiguity and provide useful biopharmaceutical information.