CYP3A4, effect intestinal

The co-administration of drugs which induce the metabolic enzymes in the liver or small intestine can reduce the plasma concentrations of drugs which are substrates of the enzyme, leading to reduced drug effects. For example, the plasma concentrations of many drugs which are substrates of the enzyme CYP3A4, such as cyclosporine, are decreased by coadministration of rifampicin, which is an inducer of CYP3A4. 

St. John s wort, which has become very popular for the treatment of depression, has been shown to induce intestinal P-gp and intestinal and hepatic CYP3A4 in humans [140]. That mechanism explains the significant reduction in cyclosporin and anti-aids (e.g., indinavir) plasma concentrations. It is likely that similar effects will be noted with the compounds listed in Table 8 (although the effects noted in Table 8 are in the opposite direction of those seen in the presence of St. John s wort). 

Ito, K., Kusuhara, H., Sugiyama, Y., Effects of intestinal CYP3A4 and P-glycoprotein on oral drug absorption -theoretical approach, Pharm. Res. 

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