Danazol increases the oral bioavailability of midazolam by inactivation of hepatic and intestinal CYP3A in rats.

Danazol (DNZ) is a synthetic androgen derivative used for the treatment of intractable hematological disorders. In this study, we investigated the effects of DNZ on CYP3A activity in hepatic and small intestinal microsomes and the pharmacokinetics of midazolam (MDZ), a typical substrate for CYP3A, in rats.MDZ 4-hydroxylation activities in hepatic and small intestinal microsomes significantly decreased 24 h after DNZ (100 mg/kg, i.p.) treatment. Time-dependent inactivation of MDZ 4-hydroxylation activities was noted when microsomes were pre-incubated with DNZ in the presence of a NADPH-generating system.The Western blot analysis indicated that the decrease observed in enzyme activity was not due to changes in the protein expression of CYP3A.In contrast to the intravenous administration, serum MDZ concentrations in DNZ-treated rats were markedly higher than those in control rats when administered orally. DNZ treatment increased MDZ oral bioavailability by approximately 2.5-folds.We herein demonstrated that DNZ increased the bioavailability of orally administered MDZ through irreversible inactivation of hepatic and intestinal CYP3A in rats.