The cytochrome P450 enzyme CYP3A4 is highly expressed in the intestinal mucosa, where it plays a critical role in the firstpass metabolism of orally administered drugs and thereby influences systemic bioavailability and drug response.For example, approximately 45％ of an oral dose of the sedative/hypnotic agent midazolam can be inactivated by CYP3A4dependent 1 and 4hydroxylation, necessitating a higher oral dose than an intravenous dose to achieve adequate pharmacological response [1].Unfortunately, there is substantial interindividual variability in thelevel of CYP3A4 expressed in the small intestine and this contributes to unpredictability in patient response to thisdrug and the many other high firstpass CYP3A4 substrates.