Pharmacokinetics of the etonogestrel contraceptive implant in obese women

Abstract

Objective: We sought to examine the pharmacokinetics and acceptability of the etonogestrel contraceptive implant in obese women.

Study design: We developed and validated a plasma etonogestrel concentration assay and enrolled 13 obese (body mass index ≥30) women and 4 normal-weight (body mass index <25) women, who ensured comparability with historical controls. Etonogestrel concentrations were measured at 50-hour intervals through 300 hours postinsertion, then at 3 and 6 months to establish a pharmacokinetic curve.

Results: All obese participants were African American, while all normal-weight participants were white. Across time, the plasma etonogestrel concentrations in obese women were lower than published values for normal-weight women and 31-63% lower than in the normal-weight study cohort, although these differences were not statistically significant. The implant device was found highly acceptable among obese women.

Conclusion: Obese women have lower plasma etonogestrel concentration than normal-weight women in the first 6 months after implant insertion. These findings should not be interpreted as decreased contraceptive effectiveness without additional considerations.