Simultaneous determination of probe drugs, metabolites, inhibitors and inducer in human plasma by liquid chromatography/tandem mass spectrometry and its application to pharmacokinetic study.

Cytochrome P450 3A4 (CYP3A4) and UDP-glucuronosyltransferase 1A1 (UGT1A1) are important enzymes responsible for the metabolism of many xenobiotics. To investigate their induction and inhibition properties, administering probe drugs and monitoring their concentration in plasma under the effects of inducers/inhibitors is the gold standard method. A rapid and sensitive liquid chromatography-tandem mass spectrometry method was developed for simultaneous quantification of midazolam, raltegravir (probe drugs for CYP3A4 and UGT1A1), their major metabolites, 1'-hydroxymidazolam, 1'-hydroxymidazolam glucuronide and raltegravir glucuronide, rifampicin (inducer), ritonavir and ketoconazole (inhibitors).