Inductive effects of fenofibrate and metabolism of phenobarbital.

The inductive effects of fenofibrate (FF) and phenobarbital (PB) were investigated in male Wistar rats. FF treatment produced an inductive effect on liver weight, cytochrome P450 content, and aniline hydroxylase (AH) and bilirubin UDP-glucuronosyltransferase (UDP-GT) activities in liver microsome fraction. PB and FF inductive effects were additive on liver weight but were not additive on P450 microsomal concentrations. On the contrary, FF administration decreased the inductive effect of PB on bilirubin UDP-GT activity. When FF and PB treatment were coupled, plasma and liver PB concentrations were not affected, whereas OHPB concentrations, especially in liver homogenate, were greatly decreased. Thus it can be concluded that the production of OHPB from PB was probably not accelerated, but the elimination of OHPB, the main metabolite of PB, was considerably enhanced. These results are to be compared with recent reports of structure-dependent induction of bilirubin glucuronidation by arylcarboxylic acids chemically related to clofibrate.