The induction of cytochrome P450 3A5 (CYP3A5) in the human liver and intestine is mediated by the xenobiotic sensors pregnane X receptor (PXR) and constitutively activated receptor (CAR).

Induction of cytochrome P450 3A (CYP3A) by xenobiotics may lead to clinically relevant drug interactions. In contrast with other CYP3A family members, studies on the inducibility of CYP3A5 indicate conflicting results. We report the induction of CYP3A5 mRNA in 13 of 16 hepatocyte preparations exposed to rifampin. Furthermore, induction of CYP3A5 mRNA was observed in intestinal biopsies in three of eight probands following exposure to the antibiotic. The highest absolute levels of CYP3A5 transcripts were found following rifampin treatment in hepatocytes and intestines from carriers of CYP3A5*1 alleles. Elucidation of the mechanism involved in CYP3A5 induction revealed that constitutively act…