Antibiotics have no effect on oral contraceptivesStudies have shown that the use of such broad-spectrum antibiotics as amoxicillin and tetracycline do not reduce the efficacy of oral contraceptives (OCs) (Murphy A et al. Am J Obstet Gynecol. 1991;164:28-33 and Helms SE et al. J Am Acad Dermatol. 1997;36:705-710). While it is true that lower serum ethinyl estradiol and progestin levels have been found in women using combination OCs and antibiotics, these women remain well within the therapeutic window.
The World Health Organization's Medical Eligibility Criteria for Contraceptive Use and the CDC's U.S. Medical Eligibility Criteria for Contraceptive Use classify antibiotics (with the exception of rifampicin and griseofulvin) as Category 1 (no restrictions on use).
Too often, women using antibiotics frequently or chronically simply stop their combination OC, thereby putting themselves at risk for pregnancy. — Beth Kutler, FNP-C, Ithaca, N.Y.
It is true that, thankfully, most current sources agree that antibiotic use does not inactivate OCs. However, it is also true that the typical OC doses are now much lower than they used to be, and many times clinicians cannot assure the dosing adherence of our patients with those low-dose pills. Consequently, we may be unwittingly putting patients at risk of unintended pregnancy in cases where hormone levels may already be precarious and, when nudged a little lower by concomitant medications, fail to do their job.
Two other classes of drugs that are rapidly rising in use are anti-epileptics and atypical antipsychotics. As strong competitors in the cytochrome P450 chain, these drugs have significant impact on the metabolism of OCs, and careful consideration should be given to using a higher-dose OC or alternative method in patients using these medications. — Sherril Sego, FNP-C, DNP (154-15)