Two or more drugs administered in therapeutic dosages at the same time or in close sequence, may act (1) independently, (2) interact to increase or diminish the effect of one or more drugs, or (3) interact to cause an unintended reaction. Potentially serious interactions can occur between antibacterial agents and other medications. An awareness of the patient’s medical history, including medications taken, is helpful in minimizing or avoiding potential drug-drug interactions. Two excellent reviews of the subject are presented elsewhere.148,149
However, the theoretical possibility that antibacterial agents may reduce the efficacy of oral contraceptives must be addressed directly. An exhaustive review of the literature found no credible pharmacokinetic data, with the possible exception of rifampin, to substantiate such interactions.150 The U.S. District Court for the Northern District of California also concluded that "scientific evidence regarding the alleged interaction between antibacterial agents and oral contraceptives" does not satisfy the "Daubert standard of causality."151
However, the American Medical Association states that such interactions cannot be completely discounted and recommends that women be informed of the possibility of such interactions.152 Similarly, the American Dental Association Council on Scientific Affairs recommends (1) that patients be advised of the potential risk, (2) that patients comply with their oral contraceptive regimen, and (3) that patients consider alternative contraception during periods of antibacterial chemotherapy.153,154
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