Oral contraceptives can be inhibited by antibiotics.

Doctors and auxiliaries should be aware of possibly reduced effectiveness of oral contraceptives (birth control pills) when simultaneously taking antibiotics. Although this effect is usually associated with broad-spectrum antibiotics, any antibiotic could result in unplanned pregnancy. All women of child-bearing age should be warned of this possibility when prescribing any antibiotics. There have been anecdotal reports of dentists and physicians being sued by women who became pregnant while on antibiotic therapy.

Modern birth control pills are estrogen, which inhibit implantation of the fertilized ovum into the uterus. Doctors are concerned about possible harmful effects of estrogen in high doses, so contraceptives have been developed (and are in wide use) that are low-dose estrogen. This is possible because estrogen is a steroid (fat soluble) hormone that is recycled via the hepato-enteric pathway. That is, estrogen taken orally is absorbed into the bloodstream, and also by the liver. In the liver, estrogen is concentrated in bile (fluid used by the body to help digest fats), which is periodically secreted into the gut. The bile estrogen is reabsorbed in the intestines with the help of commensal (naturally helpful) bacteria that live in the gut.

When the woman is taking antibiotics, sometimes the intestinal bacteria are inhibited, which in turn inhibits the usual re-absorption of estrogen. This results in lower blood estrogen, and potentially ineffective contraception.

During brief periods of simultaneous antibiotic administration, women are cautioned to use additional means of contraception. This should continue for the remainder of the monthly cycle. Patients are directed to their physician for information on additional contraceptive alternatives.

ADAA Editorial Director's Note:

Be sure to ask health history questions For Women Only--Are you pregnant? Are you taking birth control pills? And as always at every appointment ask your patient if there have been any changes in their health history/medications in addition to the six-month Health History updates--signed and dated by both the patient and the dentist.