FAMILY MEDICINE® COLUMN

By John C. Wolf, D.O.Associate Professor of Family Medicine Ohio University College of Osteopathic Medicine

ANTIBIOTICS REDUCE EFFECTIVENESS OF "THE PILL" -- VERY SLIGHTLY

Question: My ob/gyn doctor has prescribed Ortho Tri-Cyclen as my birth control pill. My dermatologist has just prescribed a tetracycline called Sumycin to be taken twice each day for three months. My dermatologist says that I shouldn't worry about the tetracycline reducing the efficacy of my birth control pills. Despite his reassurance, I checked with my pharmacist. He told me the same thing. I was OK with this until I read the pages that the pharmacy printed with my tetracycline prescription. They say that the drug may reduce the effectiveness of the birth control pill. I'm getting married in a month and don't want to get pregnant right away. Who should I believe about my medicines?

Answer: It is certainly easy to understand your confusion. Medical literature is often like this, too -- one trusted expert saying something that is in direct conflict with the research of another equally trusted expert. Your dilemma, however, isn't a consequence of differing research results. Instead, it reflects the difficulty of medical practice today.

Birth control pills work by a form of trickery. They fool your ovaries into acting as if you are pregnant. Consequently, your ovaries don't ripen another egg until this medicine induced "pregnancy" is over. The absence of a fertile or "ripe" egg also means that you can't get pregnant. This is effective, but not perfectly so. Out of 100 women who are taking "the pill," only one to two will become pregnant over the course of a year. This compares to 80 of the 100 if no birth control measures are used.

The hormones used in birth control pills are metabolized within the liver. This is not unique as almost all foods and medicines are also modified by this essential organ and, thereby, prepared for use by your body and/or for elimination. A problem, however, can develop if certain other drugs are being metabolized within the liver at the same time as the hormones from your birth control pill. The drugs in question are ones that require the same enzyme system for metabolism as the birth control pills. If these drugs "compete" for the enzyme system with the hormones from your birth control pill, it could result in an altered hormone level in your blood. In the worst case, the levels may drop sufficiently to allow an egg to ripen. That event, as you know, can allow a sexually active woman to become pregnant.

I'll give a brief list of medicines that are known to alter the level of birth control hormones when they are taken together. They are: sulfonamide antibiotics, tetracycline antibiotics, phenytoin seizure drugs, penicillin antibiotics, quinolone antibiotics, cephalosporin antibiotics, erythromycin and similar macrolide antibiotics, and barbiturate seizure medicines. There are others on this long list of drugs with this undesirable interaction.

So why did your ob/gyn doctor and your pharmacist tell you that you shouldn't be worried? Well, I think that you can safely assume that they knew this information. The absolute risk of having one of these medicines cause a birth control failure is small -- perhaps increasing the rate of pregnancy to slightly more than two per 100 women per year. They hoped to reassure you by saying that you shouldn't be concerned because the magnitude of increased risk is small. The drug manufacturer, on the other hand, is obligated by its legal advisers and by your need to know, to inform you that there is some measure of increased risk of pregnancy.

So what should you do? That is your choice. The only birth control method that is perfect is abstinence -- and that isn't a good choice for you newlyweds. If you are troubled by the small but real risk of pregnancy, then you should simultaneously use two methods of birth control. As an example, continue to take the birth control pills and also use a condom. It is your life and your choice, but make it an informed choice. Ask questions until you understand the answers.

"Family Medicine" is a weekly column.

To submit questions, write to: John C. Wolf, D.O., Ohio University College of Osteopathic Medicine, Grosvenor Hall, Athens, Ohio 45701.

Past columns are available online at http://www.FamilyMedicineNews.org.