rifampin and etonogestrel

Rifampin, a strong CYP3A inducer, is the gold standard for evaluating CYP3A-mediated drug-drug interactions. We aimed to evaluate the pharmacokinetic and pharmacodynamic effects of a short course (2 weeks) of rifampin on serum etonogestrel (ENG) concentrations and serologic measures of ovarian activity (endogenous estradiol [E2] and progesterone [P4]) among ENG implant users.. We enrolled healthy females using ENG implants for 12 to 36 months. We measured baseline serum ENG concentrations using a validated liquid chromatography mass-spectrometry assay and baseline E2 and P4 concentrations using chemiluminescent immunoassays. After 2 weeks of rifampin 600 mg daily, we repeated ENG, E2, and P4 measurements. We compared pre- and post-rifampin serum measurements using paired Wilcoxon signed-rank tests.. With only short exposure to a strong CYP3A inducer, ENG implant users experienced clinically significant decreases in serum ENG concentrations that led to changes in biomarkers indicative of waning suppression of ovulation.. Even a short, 2-week course of treatment with rifampin places etonogestrel contraceptive implant users at risk for decreased contraceptive efficacy. Clinicians should counsel patients using etonogestrel implants considering any duration of rifampin therapy on the need for backup nonhormonal contraception or the use of an intrauterine device to avoid unintended pregnancies.

Topics: Adult; Biomarkers; Contraceptive Agents, Female; Cytochrome P-450 CYP3A Inducers; Desogestrel; Drug Implants; Female; Humans; Ovulation; Pregnancy; Rifampin; Young Adult

Topics: Adult; Contraceptive Agents, Female; Desogestrel; Drug Interactions; Female; Humans; Pregnancy; Rifampin