Review of alterations in oral phenytoin bioavailability associated with formulation, antacids, and food.

Since 1938, phenytoin has been widely used for the control of seizure disorders. Phenytoin is available from a variety of manufacturers in a variety of dosage forms. Certain physiochemical properties of phenytoin may lead to bioavailability changes. The physiochemical properties exert themselves not only in the presence of other drugs but also during the manufacturing process. Manufacturing processes that may influence phenytoin bioavailability include salt form, particle size, product excipient, and dosage form. Drug influences upon phenytoin bioavailability largely include antacid anions, which may form insoluble complexes. Anions present within the diet may also influence the rate and extent of phenytoin absorption. This article reviews the various influences on phenytoin bioavailability with regard to the manufacturing process, antacid, and food.