Q. I am pregnant and I believe it is because of an antibiotic my doctor prescribed. He says that is impossible and that I must have skipped a pill. I am extremely conscientious about my birth control pills. It makes me mad that he is treating me like an airhead.
I seem to recall a column you wrote about this issue. Please tell me whether antibiotics can affect contraceptive potency.
A. You are not the first woman to report an unplanned pregnancy while taking birth control pills. We received the following letter:
“I am seven months pregnant although I never missed a single day of my birth control pills. But when I came down with bronchitis, the doctor prescribed an antibiotic. Neither the physician nor the pharmacy warned me about a potential interaction, and I was too busy being sick to think about my oral contraceptive not working.
“Although my significant other and I have been together for some time, we are not married. Try to imagine the havoc this has caused in both our lives. When pregnancy occurs out of your control, you cannot begin to imagine the possible damage, the heartache and the worry. I hope that more people tell their stories, and that something can be done to warn users of oral contraceptives.”
This interaction is highly controversial. Despite the fact that birth control pills have been on the market for many decades, there is still a paucity of high-quality research to determine whether there really is an interaction between antibiotics and oral contraceptives.
We were able to locate one article in the journal Obstetrics and Gynecology (Nov. 2001) with the following conclusion:
“Rifampin impairs the effectiveness of OCs [oral contraceptives]. Pharmacokinetic studies of other antibiotics have not shown any systematic interaction between antibiotics and OC [oral contraceptive] steroids. However, individual patients do show large decreases in the plasma concentrations of ethinyl estradiol when they take certain other antibiotics, notably tetracycline and penicillin derivatives. Because it is not possible to identify these women in advance, a cautious approach is advised.”
It is clear that there is no consensus within the medical or dental community about this potential interactions. We are interested in hearing from readers who have become pregnant while taking antibiotics and birth control pills. In the meantime, we think that prudent women will use backup methods of contraception when they must take antibiotics.