Decreased efficacy of an etonogestrel implant in a woman on antiepileptic medications: a case report

INTRODUCTION: Many antiepileptic drugs decrease the efficacy of combined hormonal contraceptives due to their inducing effect on cytochrome P450 liver metabolism. Less is known about the pharmacokinetics and outcomes of concomitant use of the etonogestrel implant and hepatic enzyme-inducing medications. CASE PRESENTATION: A 22-year-old Hispanic woman with a long-standing seizure disorder treated with carbamazepine for 9 years became pregnant after 25 months of etonogestrel implant use. CONCLUSIONS: Hepatic enzyme-inducing drugs may reduce the efficacy of contraceptive implants. Contraceptive counseling for patients with medical co-morbidities requiring hepatic enzyme-inducing medications should include this information.