Rofecoxib Is a Potent, Metabolism-Dependent Inhibitor of CYP1A2: Implications for in Vitro Prediction of Drug Interactions

Abstract

ABSTRACT:Rofecoxib was recently found to greatly increase plasma concentrations of the CYP1A2 substrate drug tizanidine in humans, but there are no published in vitro studies on the CYP1A2-inhibiting effects of rofecoxib. Our objective was to investigate whether rofecoxib is a direct-acting or metabolism-dependent inhibitor of CYP1A2 in vitro. The effect of rofecoxib on the O-deethylation of phenacetin (20 M) was studied using human liver microsomes. The effect of preincubation time on the inhibitory potential of rofecoxib was also studied, and the inhibitor concentration that supports half the maximal rate of inactivation (K I ) and the maximal rate of inactivation (k inact ) were determined. Rofecoxib is a cyclooxygenase-2-selective nonsteroidal anti-inflammatory drug, which was recently withdrawn, possibly temporarily, from clinical use because of its cardiovascular side effects. Previous studies have shown that rofecoxib moderately increases plasma concentrations and effects of theophylline (Bachmann et al., 2003) and the R-isomer of warfarin (Schwartz et al., 2000). Quite recently, rofecoxib in therapeutic doses of 25 mg per day was found to increase more than 10-fold the plasma concentrations of the CYP1A2 substrate tizanidine in humans (Backman et al., 2006b). The effects on tizanidine pharmacokinetics suggest that rofecoxib can be a relatively potent inhibitor of CYP1A2. However, hitherto, there have been no published in vitro studies on the effect of rofecoxib on CYP1A2 activity, nor has the type of CYP1A2 inhibition by rofecoxib been clarified.Rofecoxib itself is extensively metabolized via complex oxidative, reductive, and back-reduction pathways (Fig. 1) (Merck & Co., 2002;Slaughter et al., 2003). In human liver microsomal incubations, rofecoxib has been found to be metabolized to 5-hydroxyrofecoxib by several P450 enzymes, CYP1A2 and CYP3A4 having the greatest contributions . In liver S9 fractions, the metabolite profile of rofecoxib has been more complex, including the formation of both 5-hydroxyrofecoxib and different 3,4-dihydrohydroxy acid derivatives; the latter are considered to represent the major pathways in vivo (Halpin et al., 2002). Thus, it has been suggested that P450 enzymes play a minor role in rofecoxib's metabolism. However, in our recent study, the plasma concentrations of rofecoxib correlated to the plasma caffeine-paraxanthine ratio in vivo, suggesting a role for CYP1A2 in the metabolism of rofecoxib (Backman et al., 2006b). Our purpose, in the current study, was to explore in vitro the CYP1A2-inhibitory potency of rofecoxib and to elucidate the type of possible CYP1A2 inhibition. Materials and Methods Chemicals and Microsomes. Rofecoxib (Sequoia Research ProductsLimited, Pangbourne, UK), phenacetin, acetaminophen, ␤-NADPH (SigmaAldrich, St. Louis, MO), methanol, acetonitrile, and ethyl acetate (Rathburn Chemicals Ltd., Walkerburn, Scotland) were used in this study. Other chemicals were obtained from Merck (Darmstadt, Germany). Pooled human liver microsomes were obtained from BD ...

In vitro Inhibition of CYP1A2 by Model Inhibitors, Anti‐Inflammatory Analgesics and Female Sex Steroids: Predictability of in vivo Interactions

“…However, the inhibitory effects of rofecoxib, progesterone and desogestrel were increased by pre-incubation. More elaborate experimental designs [17,28] for metabolismdependent inhibition were not used, because the purpose of the study was only to screen for time-dependent inhibition.…”

“…Also, the effect of rofecoxib on tizanidine pharmacokinetics was underestimated when only its competitive inhibitory effect was considered. Our recent in vitro studies revealed that the mechanism-based inhibition of CYP1A2 would alone rather accurately predict the effect of rofecoxib on the plasma concentrations of tizanidine [17].…”

“…Among NSAIDs, rofecoxib was found to be a potent mechanismbased inhibitor of CYP1A2 in vitro [17]. Furthermore, the fenamate tolfenamic acid is a potent inhibitor of CYP1A2 in vitro [18].…”

“…Paracetamol (the product of phenacetin O-deethylation) and hydrochlorothiazide were extracted with 5.0 ml of ethyl acetate for 20 min. and the drug concentrations were measured as described earlier [17]. The limit of quantification for paracetamol was 40 nM.…”

In Vitro and in Silico Identification and Characterization of Thiabendazole as a Mechanism-Based Inhibitor of CYP1A2 and Simulation of Possible Pharmacokinetic Drug-Drug Interactions

“…These simulation results imply accumulation of TBZ with possible MBI activity on CYP1A2. The great impact of TBZ on its own elimination could partly be explained by it potentially being solely metabolized by CYP1A2 (fm 1A2 ϭ 1.0), whereas the drugs theophylline (fm 1A2 ϭ 0.85) (Monks et al, 1979) and caffeine (fm 1A2 ϭ 0.98) (Karjalainen et al, 2006) could be eliminated by other pathways.…”