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Contraception. 1980 Feb;21(2):135-43.

The effect of rifampicin on the pharmacokinetics of ethynylestradiol in women.

Abstract

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.

PIP:

7 female patients between ages 18-42 who were receiving treatment with rifampicin (450-600 mg daily) for tuberculosis were given a single dose of Minovlar (50 mg ethynlestradiol (EE) and 1 mg norethindrone acetate) and given a dose 1 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 0.01). The terminal plasma half-life increased from 2.9 + - 0.8 h to 6.3 + - 1.4 h (p 0.005). The sex hormone binding globulin capacity was reduced from 213.4 + - 11.5 nmoles to 129.0 + - 7.7 nmoles-1 after stopping rifampicin. In 1 patient starting rifampicin who was taking Minovlar as a long-term contraceptive, a decline in the plasma EE concentration was associated with an increase in the plasma follicle stimulating hormone concentration. Women taking oral contraceptive steroids and rifampicin at the same time are likely to suffer a decrease in the effectiveness of the OC. It is suggested that it is unwise for women taking rifampicin to use OCs as the sole method of contraception.

PMID:
7189454
DOI:
10.1016/0010-7824(80)90125-0
[Indexed for MEDLINE]

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