Plasma rifampicin levels during oral contraception

Gupta, K.C.; Joshi, J.V.; Anklesaria, P.S.; Shah, R.S.; Satoskar, R.S.

Journal of the Association of Physicians of India 36(6): 365-366


ISSN/ISBN: 0004-5772
PMID: 3182712
Document Number: 366229
Researchers conducted a study on the effect of oral contraceptives (OCs) on rifampicin plasma levels in 6 healthy women between 19-38 years old. These women's weight ranged between 40-60 kg an their height between 150-160 cms. All hemoglobin levels were 10 g. They had not used OCs for 3 months before the research began. As a control, the volunteers 1st did not receive an OC and had a menstrual cycle. Blood samples were collected between days 15-28 of the menstrual cycle. They took a daily low dose OC containing 1 mg norethisterone acetate and 30 mcg ethinyl estradiol in the next cycle. Before and after the 2nd OC cycle, they took 450 mg of rifampicin while the stomach was void and laboratory personnel estimated plasma levels of rifampicin by microbiological assay at 0, 1, 2, 4, 6 and 8 hours. When the women were taking no OC, peak plasma levels of rifampicin ranged between 8.2-36 mcg/ml, while they varied between 11.25-29 mcg/dl during the 2nd OC cycle. Further, the time of peak concentration of rifampicin when the women did not use an OC occurred between 2-4 hours in 5 women and at 6 hours for the other woman. During OC administration, all the women's peak concentration was 2 or 4 hours. The area under curve (AUC) of rifampicin while no OC was used extended from 29.85-176 + or - 22.1 mcg/ml/hour and 61.9-157.7 + or - 14.9 mcg/ml/hour while the women took the OC. No significant difference existed between before and during OC use plasma levels of rifampicin and AUC. Even though studies show that rifampicin treatment reduces plasma levels of OCs, these results demonstrate that a low dose OC does not change rifampicin levels.

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