An interpretation of the diffusion-type mechanism of drug release from microcapsules

Salbutamol sulfate microcapsules were prepared by a spray-drying technique. The release data were calculated approximately via standard equations (square root and first-order relationships), but unequivocal evidence in support of the cumulative release mechanism was not obtained. Even more stringent mathematical or statistical (Durbin-Watson analysis) methods did not allow any distinction to be made between the two release mechanisms. In contrast, on application of the simple power law expression Mt/M∞ = ktn proposed by Peppas the value of the kinetic exponent of release (about 0.4) indicated a diffusion-type mechanism of the release process relative to the microcapsule shape. Therefore, it suggested here that this power law expression can be applied in order to confirm the actual diffusion-type mechanism of drug release from microcapsules.