LAUSR

Graphical abstract Figure. No Caption available. HighlightsAn LC–MS method for the simultaneous determination of RIF and RIF‐Q was first developed and validated.A large amount of RIF‐Q was reduced to RIF and underwent redox cycle.CPR and NOQ1 reduced RIF‐Q to RIF and mediated the redox cycle.The redox cycle of RIF‐Q induced ROS formation and caused cytotoxicity in HepG2 cells. ABSTRACT Rifampicin (RIF) is used in regimens for infections caused by Mycobacteria accompanied by serious adverse reactions. Rifampicin‐quinone (RIF‐Q) is a major autoxidation product of RIF. It is not clear whether RIF‐Q plays a role in RIF induced adverse reactions. Investigation of the systemic exposure of RIF‐Q is helpful to better understand the role of RIF‐Q in RIF induced adverse reactions. In this study, a simple and reproducible high performance liquid chromatography‐mass spectrometry (LC–MS) method involving a procedure to prevent the RIF from oxidation for simultaneous quantification of RIF and RIF‐Q in rat plasma has been developed and validated, and applied to elucidate the systemic exposure of RIF‐Q in rats. The pharmacokinetics data showed that the systemic exposure of RIF‐Q was very low (0.67% of RIF, AUC0‐24) in rats after oral administration of RIF. However, RIF‐Q may undergo the redox cycle in vivo by the evidence that the majority of RIF‐Q was reduced to RIF after an oral dose of RIF‐Q. Pretreatment with the NAD(P)H: quinone oxidoreductase 1 (NQO1) specific inhibitor dicoumarol and/or cytochrome P450 reductase (CPR) inhibitor diphenyleneiodonium suppressed the redox cycle and significantly increased the systemic exposure of RIF‐Q. The inhibitors also attenuated the redox cycle induced reactive oxygen species formation and cytotoxicity in RIF‐Q‐treated HepG2 cells. These results indicate that NQO1 and CPR play an important role in redox cycle of RIF‐Q and may thus contribute to RIF‐induced adverse reactions.