Different Effects of Ketoconazole on the Stereoselective First-Pass Metabolism of R/S-Verapamil in the Intestine and the Liver: Important for the Mechanistic Understanding of First-Pass Drug-Drug Interactions

Abstract

ABSTRACT:In this acute study a pig jejunal intestinal perfusion model with multiple plasma sampling sites and three different administration routes was used to investigate the quantitative contribution of the intestine versus liver to the first-pass extraction of each enantiomer of verapamil (VER). A subclinical dose of ketoconazole (8 mg) was coadministered in the perfusion solution to selectively inhibit gut wall CYP3A. Both enantiomers of VER and its main metabolite norverapamil (NOR) as well as the inhibitor ketoconazole were quantified in all plasma compartments by liquid chromatographytandem mass spectrometry. The overall first-pass metabolic extraction of VER and the metabolite NOR was shown to be stereoselective with the S-isomer being more extensively extracted. For VER the ratio of R-enantiomer to S-enantiomer was greater in the hepatic vein than in the portal vein (ϳ2.2 versus 1.4), indicating that the stereoselective metabolism of VER in pigs mainly occurs on the first pass through the liver and not in the intestine. Ketoconazole increased the area under the curve from time 0 to 6 h and C max of R-and S-VER at least 3-fold in the portal vein, most likely explained by inhibition of gut wall metabolism. Conversely, hepatic extraction was increased because the effect of gut wall metabolism was not observed at the peripheral sampling sites. In conclusion, this study provided novel and more direct information on the contribution of the intestine and the liver, respectively, to the overall first-pass extraction of racemic VER.

Effects of Ketoconazole on the In Vivo Biotransformation and Hepatobiliary Transport of the Thrombin Inhibitor AZD0837 in Pigs

“…Pigs of the same age (10 -12 weeks) and breed as the ones included in the present study had a CYP3A hepatic mRNA content ranging from 0.7 to 2.0 when normalized to ␤-actin (n ϭ 8) (data on file). In addition, the plasma pharmacokinetics of other CYP3A4 substrates investigated in pigs by our group have been shown to vary to the same degree as those of AZD0837 and its metabolites (Thörn et al, 2009). The excretion of AR-H067637 into bile was very extensive, not only after enteral administration, but also after separate intravenous dosing of the prodrug and the active compound, respectively.…”

“…The pig, with a gastrointestinal tract anatomically and physiologically resembling that in human, is well suited for bioavailability and pharmacokinetic studies (Krishnan et al, 1994;Martinez et al, 2002). With regard to metabolism, it has been shown to be a suitable model of human CYP3A, displaying enzymatic activity toward prototypical substrates similar to that of the human isoforms (Soucek et al, 2001;Anzenbacherová et al, 2005;Thörn et al, 2009). The literature on transport proteins in pigs is less detailed, but several drug-relevant transporters are known to be expressed in pigs, and drugs dependent on carrier-mediated transport in their clinical disposition have been shown to display similar in vivo pharmacokinetics in pigs and humans (Goh et al, 2002;Török et al, 2003;Sjödin et al, 2008;Bergman et al, 2009).…”

In Vivo Investigation in Pigs of Intestinal Absorption, Hepatobiliary Disposition, and Metabolism of the 5α-Reductase Inhibitor Finasteride and the Effects of Coadministered Ketoconazole

“…Inhibition of CYP3A-mediated metabolism by ketoconazole has been reported in pig intestinal microsomes (Lampen et al, 1996). In addition, in two previously reported pig studies, ketoconazole inhibited the stereoselective gut wall metabolism of the CYP3A4 substrates S-and R-verapamil (Thörn et al, 2009) and the metabolism of tacrolimus (Sano et al, 2002). This study gives further evidence that the pig is a relevant model animal for CYP3A substrates.…”

“…The same type of phenomenon was found also for R-and S-verapamil when the gut wall metabolism was inhibited by ketoconazole and the AUC in the VP was increased (Thörn et al, 2009). As with finasteride, an increased E H was observed with the higher VP concentrations, and it was suggested to be the result of saturable plasma protein binding for Rand S-verapamil (Thörn et al, 2009). A possible hypothesis for the FIG.…”

“…The pig model enables sampling from the portal vein (VP), the hepatic vein (VH), and the femoral vein (VF) and bile collection directly from the biliary duct. This has made it possible to perform in-depth investigations on the effects of several DDIs on intestinal absorption, intestinal metabolism, liver metabolism, and hepatobiliary disposition (Petri et al, 2006;Sjödin et al, 2008;Bergman et al, 2009;Thörn et al, 2009). In this study, the model was used to examine in detail the effects of ketoconazole-inhibited CYP3A-mediated metabolism on the PK of finasteride.…”