Etonogestrel contraceptive implant failure in a woman taking rifampin: a case report

BACKGROUND: The etonogestrel subdermal implant is the most efficacious hormonal contraceptive currently available and provides 99.7% effective contraception. However, similar to other hormonal contraception, its effectiveness is compromised with the use of cytochrome P450 inducing drugs resulting in an unplanned pregnancy. Despite this risk, little is known about the outcome of concomitant use of rifampin and contraceptive implants. CASE PRESENTATION: A 24-year-old woman was provided with an etonogestrel implant in September 2018. In July 2020, she was started with rifampin based anti-tuberculosis for tuberculosis of the lymph nodes. In December 2020, she presented to the family planning clinic of St. Paul’s Hospital Millennium Medical college with a diagnosis of failed implant and second-trimester pregnancy at a gestational age of 19 weeks. The etonogestrel implant was removed and the patient was linked to antenatal care follow up. CONCLUSION: Concomitant use of hepatic cytochrome P450 enzyme-inducing medications with certain hormonal contraceptives may reduce effectiveness resulting in unintended pregnancy. Women should be given detailed counseling about the potential for drug interactions and a multidisciplinary approach with consultation or referral to reproductive health specialists is crucial for optimal management of women who are at increased risk of contraceptive failure and unintended pregnancy.