Journal
JOURNAL OF CLINICAL PHARMACOLOGY
Volume 45, Issue 12, Pages 1413-1421Publisher
WILEY
DOI: 10.1177/0091270005280851
Keywords
oral contraceptives; cocktail; cytochrome P450; drug-metabolizing enzymes
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The effects of a common oral contraceptive preparation oil the activity of 7drug-metabolizing enzymes were investigated using the validated Cooperstown 5+1 Cocktail. In a randomized crossover fashion, 10 premenopausal women received caffeine, dextromethorphan, omeprazole, intravenous midazolam, and warfarin + vitamin K with and without a triphasic oral contraceptive (ethinyl estradiol 35 mu g) and varying doses of daily norgestimate (0. 18, 0.215, and 0.25 mg). Bioequivalence testing showed nonequivolence in drug versus no-drug treatment on the activity of drug-metabolizing enzymes (as reflected by metabolite ratios following probe drug admimstration); the activity of CYP1A2, CYP2C19, and NAT-2 decreased following g the oral contraceptive, whereas the activity of CYP2C9 and CYP2D6 increased. No effects on xanthine oxidase or hepatic CYP3A were seen. Application of a non-parametric statistical testing approach revealed a significant difference only for CYP1A2 and CYP2C19. This triphasic oral contraceptive may have a clinically significant effect on the activity of some drug-metabolizing enzymes.
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