The effect of rifampicin on the pharmacokinetics of ethynylestradiol in women.
A single dose of Minovlar (50 microgram ethynylestradiol (EE) and 1 mg norethindrone acetate) was given to seven women during treatment with rifampicin (450-600 mg/day) and again one month after stopping rifampicin. Blood samples were taken at intervals over a 24-hour period. The area under the plasma EE versus time curve increased significantly on stopping rifampicin from 1014 +/- 317 pg/ml x h (mean +/- SE) to 1747 +/- 218 pg/ml x h (p less than 0.01). The terminal plasma half-life increased from 2.9 +/- 0.8 h to 6.3 +/- 1.4 h (p less than 0.005). The sex hormone binding globulin (S.H.B.G.) capacity was also reduced from 213.4 +/- 11.5 nmoles to 129.0 +/- 7.7 nmoles/1 after stopping rifampicin. In one patient starting rifampicin who was taking Minovlar as a long-term oral contraceptive, a fall in the plasma EE concentration was associated with a rise in the plasma follicle stimulating hormone concentration. These effects of rifampicin on EE pharmacokinetics are consistent with induction of the microsomal enzymes that metabolise EE.
D000293:Adolescent; D000328:Adult; D004977:Ethambutol / Q000627:therapeutic use; D004997:Ethinyl Estradiol / Q000097:blood* / Q000494:pharmacology; D005260:Female; D006801:Humans; D007538:Isoniazid / Q000627:therapeutic use; D007700:Kinetics; D009640:Norethindrone / Q000031:analogs & derivatives / Q000097:blood / Q000494:pharmacology; D000077563:Norethindrone Acetate; D012293:Rifampin / Q000494:pharmacology* / Q000627:therapeutic use; D012738:Sex Hormone-Binding Globulin; D014376:Tuberculosis / Q000188:drug therapy
D012738:Sex Hormone-Binding Globulin; D004997:Ethinyl Estradiol; D004977:Ethambutol; D000077563:Norethindrone Acetate; D009640:Norethindrone; D007538:Isoniazid; D012293:Rifampin