Introduction
Rivaroxaban,
an
outstanding representative of a non−vitamin K oral anticoagulant,
directly inhibits Factor Xa to block the production and reduce the
activation of thrombin [1]. Compared with vitamin K
anticoagulants, rivaroxaban exerts
a more specific and powerful anticoagulant effect, and has been approved
mainly for treatment and prevention of deep venous thrombosis, pulmonary
embolism and systemic embolism from nonvalvular atrial fibrillation
[2]. In the evaluation of safety and pharmacokinetic stability,
rivaroxaban surpasses established anti-coagulant agents; however,
bleeding risk still exits [3]. A systematic review and meta-analysis
of the efficiency and safety of direct oral anticoagulants approved for
treating or preventing cardiovascular thromboembolism complications
showed that rivaroxaban did not outperform warfarin in terms of
gastrointestinal bleeding risk [4]. Indeed, several bleeding events
have been reported when rivaroxaban was applied to prevent stroke and
systemic embolism for atrial fibrillation patients, especially when used
in combination with other heart rate control drugs [5-7].
Previous studies have investigated the metabolism and elimination of
rivaroxaban, with cytochrome P450 (CYP) enzymes, mainly CYP2J2 and
CYP3A4, and a few liver hydrolytic enzymes playing an important role in
the deactivation of rivaroxaban [8 9]. The major metabolites and
metabolic pathways were identified by in vitro liver microsome
incubation studies, and
morpholinone
2- hydroxylation
(M1)
was identified as the structure of the major rivaroxaban metabolite by
H1 NMR analysis (Figure 1) [8]. As previously
reported, the proportion of rivaroxaban metabolized by CYP enzymes
represents approximately two-thirds of a given dose, and the remaining
one-third is eliminated by secretion mediated by P-glycoprotein (P-gp)
and breast cancer resistance protein (BCRP) [8 10 11].
Pharmacokinetic interactions between rivaroxaban and drugs for
regulating CYP3A4 and P-gp have been extensively evaluated, with
outcomes indicating that caution is warranted when it is used
concomitantly with strong CYP3A4 and P-gp inhibitors [12-14].
Notably, Mueck et al. found that rivaroxaban co-administrated with
strong or moderate CYP3A4 inhibitors―such as clarithromycin and
fluconazole―did not cause clinically relevant interactions for
rivaroxaban [12 14 15]. In addition, bleeding events do exist for
combining with other agents in clinical practice, which are not limited
to CYP3A4 and P-gp inhibitors [5-7 16 17]. Taken together, we
hypothesize that CYP3A4 is not the predominant isoform involved in the
metabolism of rivaroxaban, and that other CYP isoforms likely
participate to a larger extent in rivaroxaban morpholine 2-hydroxylation
[12 18].
In the present study, we systematically evaluated the participation and
contribution of a series of
CYP
isoforms in the metabolism of rivaroxaban by
product formation analysis in human
liver microsomes
(HLMs)
and recombinant human CYPs, as well as CYP-specific inhibition studies.