Method for predicting the risk of drug-drug interactions involving inhibition of intestinal CYP3A4 and P-glycoprotein

1. To develop a method to predict the risk of drug-drug interactions involving the inhibition of intestinal CYP3A4 or P-glycoprotein, data from clinical drug-drug interaction studies of CYP3A4 and/or P-glycoprotein substrates were analysed. The ratio of inhibitor dose (Dosed to inhibition constant termed the drug-interaction number, was used to index intestinal drug-drug interaction. 2. From the analysis, it was found that (1) CYP3A4 inhibitors with a drug-interaction number below 2.8 L have a low risk of interacting with substrates which exhibit intestinal first-pass metabolism and those with a drug-interaction number above 9.4 L have a high risk; (2) P-glycoprotein inhibitors with a drug-interaction number below 10.8 L have a low risk of interacting with P-glycoprotein substrates and those with a drug-interaction number above 27.9 L have a high risk; and (3) the drug-interaction number indexes, 2.8 L and 9.4 L for CYP3A4 and 10.8 L and 27.9 L for P-glycoprotein were validated by data from dual CYP3A4/P-glycoprotein substrates. 3. In conclusion, the drug-interaction number is useful for classifying the risk of drug-drug interactions involving the inhibition of intestinal CYP3A4 and P-glycoprotein. This drug-interaction number-based approach is similar to the method that the US Food and Drug Administration (USFDA) recently proposed in the draft guidance for predicting P-glycoprotein-mediated drug-drug interaction.