Gastrointestinal Transit and Concomitant Absorption of Verapamil from a Single-Unit Sustained-Release Tablet

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Abstract
A radiographic procedure is described for determining the position of a single-unit sustained-release tablet and the concomitant drug serum level. The results confirmed that, under fasting conditions, an essential part of the absorption of the model drug, verapamil, takes place in the colon. Food affected not only the gastrointestinal transit of the tablet but also the absorption rate of verapamil. With food the commencement of absorption was clearly more rapid than under fasting conditions. This is because the tablet is retained for a longer time by the food in the upper parts of the gastrointestinal tract, which favour drug absorption. It is concluded that absorption of verapamil from the colon is also effective and can be utilized in sustained release formulations. The ratio of AUC values of verapamil to those of norverapamil was markedly higher under fasting conditions, indicating enhanced bioavailability of verapamil from formulations which release most of the drug into the colon.