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Studies of hydroxypropyl methylcellulose donut-shaped tablets.

Simple uncoated compressed tablets with a central hole (donut shape) or multihole tablets were prepared. Theophylline and diltiazem hydrochloride were used as model drugs to investigate in vitro drug release from donut-shaped tablets. The effects of hole size, the number of holes, drug solubility, and stirring rate on release kinetics were investigated. As for the donut-shaped tablets, the duration of zero-order drug release could be up to 80-90%. When the hole size was increased, the release rate increased, and the duration of linear drug release was longer. The durations of linear drug release of two-hole and three-hole tablets were longer than that of the single-hole tablets. As the drug solubility increased, the duration of linear drug release was shortened. However, three stirring rates (50 rpm, 100 rpm, 150 rpm) had little effect on the drug release.