Biopharmaceutical studies on hydantoin derivatives. II. Pharmacokinetics and bioavailability of hydantoin derivatives in dogs

Pharmacokinetics and bioavailability for the 1-benzenesulfonylhydantoin derivatives and 1-unsubstituted hydantoin derivatives were evaluated from the plasma concentrations after oral and intravenous administrations to dogs. Apparent volume of distribution of the 1-benzenesulfonylhydantoin derivatives was about 0.25 l/kg, while that of the 1-unsubstituted hydantoin derivatives was about 1.3 l/kg. The result suggests that introduction of the benzenesulfonyl group at 1-position of the hydantoin ring has marked effect on the distribution into the fluids and tissues of the body. Bioavailabilities of sodium 5,5-diphenylhydantoin and sodium 1-benzenesulfonyl-5,5-diphenylhydantoin exceeded those of their corresponding free forms. The results were well explicable in terms of the excellent dissolution behaviours of the salt forms. The bioavailabilities of 5-ethyl-5-phenylhydantoin and 1-benzenesulfonyl-5-ethyl-5-phenylhydantoin were almost perfect. The results suggest that the dissolution rate is a rate-determining step in the bioavailability of the derivatives having two phenyl groups at 5-position of the hydantoin ring, irrespective of the presence of the benzenesulfonyl group at 1-position.