Hormonal contraceptives + Antibacterials; Cephalosporins - Drug Interactions

A few anecdotal cases of combined oral contraceptive failure havebeen reported with cefalexin,cefalexin with clindamycin, and unspecified cephalosporins. The interaction (if such it is) appears tobe very rare indeed.

Two pregnancies were attributed to use of cephalosporins (unspecified) and an oral contraceptive (unspecified) in adverse reactions register of CSM in UK for years 1968 to 1984 (61 cases were attributed to other antibacterials) (See reference number 1). One case of contraceptive failure has been attributed to cefalexin,(See reference number 2) and one to cefalexin used with clindamycin (See reference number 3). In a case-control study,356 women were who had received oral contraceptives and antibacterials (said to be cephalosporins, penicillins, tetracyclines) were identified over a 5-year period in 3 dermatological practices. The contraceptive failure rate in these women (1.6% per year; 2 pregnancies occurred in women taking a cephalosporin and 3 in women taking minocycline) was indistinguishable from failure rate seen in control patients taking oral contraceptives and no antibacterials (1% per year) (See reference number 4).

Suppression of intestinal bacteria, which results in reduced enterohepatic recirculation of ethinylestradiol and a fall in serum levels, is suggested explanation for any interaction (see Hormonal contraceptives and sex hormones, ). Note that broad-spectrum antibacterials do not affect progestogens,as their metabolites are inactive (See reference number 5).

The interaction between combined hormonal contraceptives and cephalosporins that are summarised here are all that have been identified in literature. These interactions are not adequately established and whole issue remains very controversial (See reference number 5). Bearing in mind extremely wide use of both groups of drugs, any increased incidence of contraceptive failure above that normally seen is clearly very low indeed. On other hand, personal and ethical consequences of an unwanted pregnancy can be very serious. For this reason, Faculty of Family Planning and Reproductive Health Care (FFPRHC) Clinical Effectiveness Unit recommends that patients taking antibacterials that do not induce liver enzymes should use a second form of non-hormonal contraception, such as condoms, while taking a short course of less than 3 weeks of a cephalosporin, and also for 7 days after antibiotic has been stopped. This advice applies to both oral and patch form of combined contraceptive (See reference number 5). For further comment and advice see also Hormonal contraceptives + Antibacterials; Penicillins interaction.

Note that antibacterials that do not induce liver enzymes do not affect reliability of progestogen-only contraceptives, see Progestogenonly contraceptives + Antibacterials, or progestogen-only emergency hormonal contraceptive, see ‘Emergency hormonal contraceptives + Antibacterials.

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Helms SE,Bredle DL, Zajic J, Jarjoura D, Brodell RT, Krishnarao I. Oral contraceptive failurerates and oral antibiotics. J Am Acad Dermatol (1997) 36, 705–10.

Faculty of Family Planning and Reproductive Health Care Clinical Effectiveness Unit.FFPRHC Guidance: Drug interactions with hormonal contraception. April 2005. Available at:http://www.ffprhc.org.uk/admin/uploads/DrugInteractionsFinal.pdf (accessed 23/08/07).