Rifampicin Clofibrate

The interaction of rifampicin with clofibrate has been reviewed (105). Rifampicin induces the metabolism of clofibrate, and in five subjects rifampicin 600 mg/day caused a 35% fall in steady-state serum clofibrate concentrations (106). 

The regulation of P450 2A6 expression has been studied in primary cultures of human hepato-cytes. Expression (mKNA, protein) is inducible by rifampicin and phenobarbitaP and, to a lesser extent, clofibrate, cobalt, griseofulvin, and pyra-zole. The nuclear receptor HNF-4 is involved in the expression of cultured hepatocytes . 

Preliminaiy evidence suggests that rifampicin can reduce the plasma levels of the active metabolite of clofibrate, but rifampicin apparently has no effect on gemfibrozil pharmacokinetics. 

A 35% reduction in the steady-state plasma levels of the active metabolite of clofibrate, ehlorophenoxyisobutyric acid (CIPB), was seen in 5 healthy subjects after they took rifampicin 600 mg daily for 7 days. This appears to occur because the metabolism of CIPB by the liver and/or the kidneys is inereased. On the basis of this study it would now be prudent to monitor serum lipid levels of patients taking clofibrate if rifampicin is added, and to increase the elofibrate dosage if necessary. More study is needed to establish this interaction. 

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