Eleanor Bimla Schwarz, MD, MS reviewing Lazorwitz A et al. Contraception 2017 Jun.
Subdermal implants may lose efficacy when used concurrently with carbamazepine.

Women with chronic medical conditions are often encouraged to time their pregnancies carefully; thus, many seek reassurance that their medications will not diminish the efficacy of their contraceptives (or vice versa). Carbamazepine causes birth defects and reduces the efficacy of oral contraceptives by inducing liver enzymes (see U.S. Medical Eligibility Criteria for Contraceptive Use). To investigate whether carbamazepine also adversely affects serum etonogestrel levels in women using subdermal contraceptive implants, researchers conducted a crossover study in 10 healthy women who had used an implant for a median of 23 months.

Median etonogestrel concentrations differed significantly before versus after carbamazepine coadministration (158.1 vs. 50.9 pg/mL, P=0.005). In 8 of 10 participants, etonogestrel concentrations fell below the threshold for ovulatory suppression (90 pg/mL) when carbamazepine was coadministered.

CITATION(S):

Lazorwitz A et al. The effect of carbamazepine on etonogestrel concentrations in contraceptive implant users. Contraception 2017 Jun; 95:571.

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