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Hot-melt extrusion with die-face pelletisation is an excellent technique to continuously produce almost monodisperse spherical starch pellets. For a better understanding of drug release mechanisms from hot-melt extruded starch-based pellets the swelling behaviour in the release medium was examined by reflected-light microscopy. From the microscopic images it can be concluded that the drug release mechanism of wx corn starch pellets is almost solely based on erosion. The release mechanism of corn starch, pea starch and potato starch pellets is primarily a swelling-based process. Although the release mechanism of a swelling dosage form is theoretically complex, it was found that the fractional drug release from the hot-melt extruded starch pellets can be described with the Noyes-Whitney equation. This facilitates the evaluation of the influence of the physicochemical properties of the matrix and the chemical properties of the active ingredient on the drug release rate. It was found that pellet size, porosity and velocity with which the penetrant diffuses into the pellet-core the water solubility of the drug as well as the molecular structure and composition of the starches are the main factors influencing drug release from the swelling starch pellets.

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