A pilot study on the effect of isotretinoin on serum etonogestrel concentrations in contraceptive implant users

Abstract

Objective: To explore the pharmacokinetic interaction between isotretinoin, a cytochrome P-450 (CYP) inducer and potent teratogen, and the etonogestrel contraceptive implant. Study design: We enrolled healthy reproductive-age women initiating isotretinoin and using an etonogestrel implant. We compared serum etonogestrel concentrations at baseline and after four and nine weeks of isotretinoin co-administration using a validated assay. Results: Among eight implant users, all serum etonogestrel concentrations remained >90 pg/mL during isotretinoin co-administration with no significant changes from baseline (p = 0.25, Friedman's test). Conclusion: In this exploratory study, we found that isotretinoin did not cause serum etonogestrel concentrations to fall below the threshold for ovulatory suppression (<90 pg/mL) among implant users. Implications: Reproductive-age women treated with isotretinoin require reliable contraception to prevent pregnancies impacted by teratogenic-effects. This small study demonstrates that contraceptive implant users maintained serum etonogestrel concentrations above the threshold for consistent ovulatory suppression during isotretinoin co-administration. The contraceptive implant remains an appropriate option for patients considering isotretinoin therapy.