WESTPORT, CT (Reuters Health) – The American Medical Association (AMA) has adopted new recommendations regarding the increased risk of oral contraceptive (OC) failure when OCs are used concomitantly with antibiotics.
Dr. Nancy H. Nielsen of Buffalo, New York and members of the AMA's Council on Scientific Affairs evaluated 167 papers published between 1966 and 1999 concerning the effects of antibiotic therapy on OC efficacy.
More than 200 episodes of OC failure were reported in case reports, adverse event monitoring systems and retrospective studies, Dr. Nielson's group reports in the November issue of Obstetrics and Gynecology. However, the rates of failure were within the usual 1% to 3% range expected with OC use.
The investigators found that rifampin, a potent inducer of cytochrome P-450-3A4, reduces plasma levels of OCs. Otherwise, the studies did not demonstrate any systematic interaction between antibiotics and OCs.
The authors point out, however, that some individuals may be predisposed to OC failure, including women with low rates of ethinyl estradiol 2-hydroxylation, high rates of hepatic conjugation, or intestinal flora particularly susceptible to the antibiotic being used.
Based on the results of this study, the AMA recommends that women who are on OCs be counseled to use a nonhormonal contraceptive method while using rifampin.
In addition, women who use combined OCs should be told of the small risk of OC failure before starting an antibiotic regimen. Those with previous OC failure or who develop breakthrough bleeding while using the antibiotic should also be advised to choose an alternate method of contraception until antibiotic treatment has ended.
Obstet Gynecol 2001;98:853-860.
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