Biopharmaceutical studies on hydantoin derivatives. IV. Factors affecting bioavailability of 5,5-diphenylhydantoin in dog.

Several factors affecting the bioavailability of 5,5-diphenylhydantoin (I) and its sodium salt (I-Na) were examined in dogs in relation to meal and following results were obtained. The bioavailability of I was not appreciably affected by the volume of coadministered water in the range of 30-120 ml. The bioavailability of I was most excellent when I was administered 0.5 h after meal. Food intake 0.5 h after drug administration enhanced appreciably the bioavailability, but that 2 h after drug administration did hardly affect the bioavailability. The extent of bioavailability of I-Na was almost 100% of the dose in the range of 100-400 mg/dog when it was administered 0.5 h after meal. While, when I-Na was administered in the fasting state, the extent of bioavailability was about 60% of the dose. Food-induced enhancement of the bioavailability of I was independent of the food constituents. The bioavailability of I was increased about 1.5-fold and 2-fold with 10-fold increase in the specific surface area of I, in the nonfasting and the fasting states, respectively. In the experiments using the dogs with the chronically implanted fistula in the common bile duct, it was found that the bile was not a major factor contributing to the food-induced enhancement of the bioavailability of I. There was a good correlation between the bioavailability of I in dog and that in man.