Abstract

A specific extraction procedure for the separation and measurement of 5,5-diphenyihydantoin (DPH), hydroxydiphenyihydantoin (HPPH) and more polar metabolites has been developed using ¹⁴C-DPH. The DPH is extracted with 1-chlorobutane, the HPPH with diethyl ether and more polar metabolites with acetone. The half-life (t/2) of DPH in the blood of the rat (male, Sprague-Dawley) after i.v. injection is dose dependent and is 0.6, 1.2 and 2.5 hours at doses of 10, 25 and 40 mg/kg, respectively. In the isolated perfused rat liver there is an initial rapid decline of DPH in the perfusate caused primarily by hepatic uptake of unchanged drug. Thereafter the decline in the perfusate is slower and the t/2 is 15 and 60 minutes at initial doses of 10 and 92 µg/ml in the perfusate. Under these conditions DPH is converted mainly to p-HPPH which undergoes conjugation. Two isomers of HPPH, p-HPPH and m-HPPH, were isolated from acid hydrolysates of bile but only p-HPPH after enzymic hydrolysis. The conjugate accumulates in the bile and perfusate. The dihydrodiol metabolite is also present in the bile and perfusate. The t/2 of p-HPPH (100 µg/ml) in the perfusate is 12 minutes. Incubations of DPH with microsomes obtained from rat liver results in the production of p-HPPH as well as more polar components. Pretreatment of rats with phenobarbital, chlordane, hydroxyzine and DDT results in an increase in the rate of disappearance of DPH from microsomal incubations and the metabolite pattern remains similar.