title: Effects of clarithromycin and verapamil on rabeprazole pharmacokinetics between CYP2C19 genotypes.
abstract: OBJECTIVE
  Rabeprazole as a proton pump inhibitor (PPI) is mainly reduced to rabeprazole thioether via a nonenzymatic pathway, with minor CYP2C19 and CYP3A4 involvement. The aim of this study was to compare possible effects of clarithromycin and verapamil as inhibitors of CYP3A4 on the pharmacokinetics of rabeprazole among CYP2C19 genotypes.
  
  
  METHODS
  A three-way randomized, double-blind, placebo-controlled crossover study was performed. Nineteen volunteers, of whom six were homozygous extensive metabolizers (EMs), eight were heterozygous EMs, and five were poor metabolizers (PMs) for CYP2C19, received three 6-day courses of either daily 800 mg clarithromycin, 240 mg verapamil, or placebo in a randomized fashion, with a single oral dose of 20 mg rabeprazole on day 6 in all cases. Plasma concentrations of rabeprazole and rabeprazole thioether were monitored up to 24 h after the dosing.
  
  
  RESULTS
  In the control phase, the AUC(0-infinity) values for rabeprazole and rabeprazole thioether were 1,005+/-366 and 412+/-149 ng.h/ml in homozygous EMs, 1,108+/-340 and 491+/-245 ng.h/ml in heterozygous EMs, and 2,697+/-364 and 2,116+/-373 ng.h/ml in PMs, respectively. There were significant differences (p<0.001) in the AUC(0-infinity) of rabeprazole and rabeprazole thioether among three different CYP2C19 genotypes. In the clarithromycin and verapamil phases, no significant differences were found in the pharmacokinetic parameters of rabeprazole compared with those in the control phase irrespective of CYP2C19 genotypes, whereas the AUC(0-infinity) of rabeprazole thioether was significantly increased 2.8-fold and 2.3-fold in homozygous EMs (p<0.01), 2.0-fold and 2.0-fold in heterozygous EMs (p<0.05), and 1.6-fold and 1.9-fold in PMs (p<0.05), respectively. In each genotype group for CYP2C19, there were no statistical differences in the percent increase in those pharmacokinetic parameters between the clarithromycin and verapamil pretreatment phases.
  
  
  CONCLUSIONS
  The pharmacokinetic parameters of rabeprazole were not altered by clarithromycin or verapamil irrespective of the CYP2C19 genotypes. However, this result shows that both clarithromycin and verapamil significantly influence the disposition of rabeprazole by inhibiting the oxidation of the thioether, since the AUC(0-infinity) of rabeprazole thioether that has no effect on acid secretion increased. Therefore, the pharmacokinetic interactions between rabeprazole and CYP3A4 or P-glycoprotein inhibitors have limited clinical significance.
authors.affiliation: Department of Clinical Pharmacology, Hirosaki University School of Medicine, Hirosaki 036-8562, Japan.
authors.forename: Mikiko
authors.initials: M
authors.lastname: Shimizu
authors.forename: Tsukasa
authors.initials: T
authors.lastname: Uno
authors.forename: Norio
authors.initials: N
authors.lastname: Yasui-Furukori
authors.forename: Kazunobu
authors.initials: K
authors.lastname: Sugawara
authors.forename: Tomonori
authors.initials: T
authors.lastname: Tateishi
mesh_terms: D053799:2-Pyridinylmethylsulfinylbenzimidazoles / Q000097:blood / Q000378:metabolism / Q000493:pharmacokinetics*; D019540:Area Under Curve; D001189:Aryl Hydrocarbon Hydroxylases / Q000187:drug effects / Q000235:genetics*; D017291:Clarithromycin / Q000494:pharmacology*; D065731:Cytochrome P-450 CYP2C19; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D004311:Double-Blind Method; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005838:Genotype; D006207:Half-Life; D006801:Humans; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D006899:Mixed Function Oxygenases / Q000187:drug effects / Q000235:genetics*; D064750:Rabeprazole; D014700:Verapamil / Q000494:pharmacology*
chemical_list: D053799:2-Pyridinylmethylsulfinylbenzimidazoles; D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D064750:Rabeprazole; D014700:Verapamil; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C045793:CYP2C19 protein, human; D065731:Cytochrome P-450 CYP2C19; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D017291:Clarithromycin