Different inhibitory effect of fluvoxamine on omeprazole metabolism between CYP2C19 genotypes.
OBJECTIVE
Omeprazole is mainly metabolized by the polymorphic cytochrome P450 (CYP) 2C19. The inhibitory effect of fluvoxamine, an inhibitor of CYP2C19 as well as CYP1A2, on the metabolism of omeprazole was compared between different genotypes for CYP2C19.


METHODS
Eighteen volunteers, of whom six were homozygous extensive metabolizers (EMs), six were heterozygous EMs and six were poor metabolizers (PMs) for CYP2C19, participated in the study. A randomized double-blind, placebo-controlled crossover study was performed. All subjects received two six-day courses of either daily 50 mg fluvoxamine or placebo in a randomized fashion with a single oral 40 mg dose of omeprazole on day six in both cases. Plasma concentrations of omeprazole and its metabolites, 5-hydroxyomeprazole, omeprazole sulphone, and fluvoxamine were monitored up to 8 h after the dosing.


RESULTS
During placebo administration, geometric means of peak concentration (C(max)), under the plasma concentration-time curve from 0 to 8 h (AUC(0,8 h)) and elimination half-life (t(1/2)) of omeprazole were 900 ng ml(-1), 1481 ng ml(-1) h, and 0.6 h in homozygous EMs, 1648 ng ml(-1), 4225 ng ml(-1) h, and 1.1 h in heterozygous EMs, and 2991 ng ml(-1), 11537 ng ml(-1) h, and 2.8 h in PMs, respectively. Fluvoxamine treatment increased C(max) of omeprazole by 3.7-fold (95%CI, 2.4, 5.0-fold, P < 0.01) and 2.0-fold (1.4, 2.6-fold, P < 0.01), AUC(0,8 h) by 6.0-fold (3.3, 8.7-fold, P < 0.001) and 2.4-fold (1.7, 3.2-fold, P < 0.01), AUC(0, infinity ) by 6.2-fold (3.0, 9.3-fold, P < 0.01) and 2.5-fold (1.6, 3.4-fold, P < 0.001) and prolonged t((1/2)) by 2.6-fold (1.9, 3.4-fold, P < 0.001) and 1.4-fold (1.02, 1.7-fold, P < 0.05), respectively. However, no pharmacokinetic parameters were changed in PMs. The AUC(0,8 h) ratios of 5-hydroxyomeprazole to omeprazole were decreased with fluvoxamine in homozygous EMs (P < 0.05) and heterozygous EMs (P < 0.01).


CONCLUSIONS
Even a low dose of fluvoxamine increased omeprazole exposure in EMs, but did not increase omeprazole exposure in PMs after a single oral dose of omeprazole. These findings confirm a potent inhibitory effect of fluvoxamine on CYP2C19 activity. The bioavailability of omeprazole might, to some extent, be increased through inhibition of P-glycoprotein during fluvoxamine treatment.
Yasui-Furukori
Norio
N
Department of Clinical Pharmacology, Hirosaki University, School of Medicine, Hirosaki, Japan. yasufuru@cc.hirosaki-u.ac.jp
Takahata
Takenori
T
Nakagami
Taku
T
Yoshiya
Gen
G
Inoue
Yoshimasa
Y
Kaneko
Sunao
S
Tateishi
Tomonori
T
D000328:Adult; D000897:Anti-Ulcer Agents / Q000037:antagonists & inhibitors*; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics*; D018592:Cross-Over Studies; D065731:Cytochrome P-450 CYP2C19; D004311:Double-Blind Method; D004347:Drug Interactions; D005260:Female; D016666:Fluvoxamine / Q000494:pharmacology*; D006579:Heterozygote; D006720:Homozygote; D006801:Humans; D008297:Male; D006899:Mixed Function Oxygenases / Q000235:genetics*; D009853:Omeprazole / Q000037:antagonists & inhibitors*; D017367:Selective Serotonin Reuptake Inhibitors / Q000494:pharmacology*
D000897:Anti-Ulcer Agents; D001189:Aryl Hydrocarbon Hydroxylases; D065731:Cytochrome P-450 CYP2C19; D016666:Fluvoxamine; D006899:Mixed Function Oxygenases; D009853:Omeprazole; D017367:Selective Serotonin Reuptake Inhibitors; C045793:CYP2C19 protein, human