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The effects of rifampin and rifabutin on the pharmacokinetics and pharmacodynamics of a combination oral contraceptive.

Authors
  • Barditch-Crovo, P
  • Trapnell, C B
  • Ette, E
  • Zacur, H A
  • Coresh, J
  • Rocco, L E
  • Hendrix, C W
  • Flexner, C
Type
Published Article
Journal
Clinical pharmacology and therapeutics
Publication Date
Apr 01, 1999
Volume
65
Issue
4
Pages
428–438
Identifiers
PMID: 10223781
Source
Medline
Keywords
License
Unknown

Abstract

The relative effects of rifampin and rifabutin (a related rifamycin) on the pharmacokinetics and pharmacodynamics of ethinyl estradiol (EE) and norethindrone were evaluated in a prospective, randomized, double-blinded crossover study in 12 premenopausal women who were on a stable oral contraceptive regimen that contained 35 mcg EE and 1 mg norethindrone. Subjects were randomized to receive 14 days of rifampin or rifabutin from days 7 through 21 of their menstrual cycle. After a 1-month washout period (only the oral contraceptives were taken), subjects were crossed over to the other rifamycin. Findings showed that rifampin significantly decreased the mean area under the plasma concentration-time curve from time 0 to 24 hours [AUC (0-24)] of EE and the mean AUC (0-24) of norethindrone. Rifabutin significantly decreased the mean AUC (0-24) of EE and the mean AUC (0-24) of norethindrone. The effect of rifampin was significantly greater than rifabutin on each AUC (0-24). Despite these changes, subjects did not ovulate (as determined by progesterone concentrations) during the cycle in which either rifamycin was administered. Levels of mean follicle-stimulating hormone increased 69% after rifampin. This study suggests that rifampin (600 mg daily) was a more important inducer of EE and norethindrone clearance than rifabutin, but none of these agents were able to reverse the suppression of ovulation done by oral contraceptives.

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