Antibiotics have been linked to a decrease in birth control efficacy, especially when in reference to oral contraceptive pills (OCPs). The MayoClinic reports that the idea that antibiotics can negatively affect birth control may be exaggerated, except in the cases of rifampin, and perhaps penicillin and tetracycline derivatives. HealthSquare.com reports that the list of antibiotics that can decrease the efficacy of birth control pills includes rifampin, chloramphenicol, and cephalosporins. If a woman is using these antibiotics while taking an OCP, she should consider using another form of birth control.
Rifampin
Rifampin is the only drug listed by MayoClinic as being positively identified as a drug that affects birth control. Most OCPs, according to Dr. Newton Osborne in his article "Antibiotics and Oral Contraceptives: Potential Interactions" in the Journal of Gynecologic Surgery, contain a type of estrogen and/or a type of progestin. Rifampin affects the metabolism of both of these hormones. Rifampin stimulates a liver enzyme called cytochrome P450, which in turn degrades any estrogen in the body. Rifampin also stimulates a binding protein that binds to progestin and makes it unavailable to the body. By preventing the body from utilizing the two main ingredients of the OCPs, rifampin severely limits the effectiveness of the birth control. Patients taking rifampin (which is most commonly used for the treatment of tuberculosis), should use another form of birth control instead of OCPs.
Chloramphenicol and Tetracycline
These two drugs have been found to cause a theoretical adverse affect in a small percentage of women who are using hormonal birth control methods, according to MayoClinic. Osborne has cited that these drugs can destroy the natural bacteria that exist in the intestines. The bacteria normally change estrogen conjugates (such as ethinyl estradiol, a common ingredient in many OCPs) into free estrogen, which can then be filtered into the blood stream. However, when chloramphenicol or tetracycline kill the bacteria, the estrogen conjugates stay in the intestine and cannot be used by the body for contraceptive purposes.
Penicillins and Cephalosporins
These two drugs are members of the safe family of antibiotics--the beta-lactams. Beta-lactams are antibiotics that target the cell wall of the bacteria. According to Osborne, these drugs inhibit the growth of the normal bacteria found in the intestine. As with chloramphenicol and tetracycline, the bets-lactams kill all the bacteria that normally convert the estrogen component of birth control pills into free estrogen that can enter the bloodstream. Thus, beta-lactams indirectly prevent estrogen from entering the bloodstream. This affects the birth control pill's ability to prevent pregnancy. Examples of these drugs include amoxicillin and cefazolin.
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