Variability in repeat serum etonogestrel concentrations among contraceptive implant users during the steady-release pharmacokinetic period

Abstract

Objective: To assess the variability of repeated measurements of serum etonogestrel concentration among contraceptive implant users.

Study design: We measured 3 consecutive serum etonogestrel concentrations, drawn weekly, in women using etonogestrel implants for 12 to 36 months. We used a repeated measures test to evaluate differences.

Results: Among 20 participants, repeat serum etonogestrel concentrations did not differ from initial measurements (Friedman's test, p = 0.95). Mean serum etonogestrel concentrations had similar 95% confidence intervals at each time point: (134.09, 201.46), (135.08, 237.46), and (132.66, 192.45).

Conclusion: We confirm that single-time measurements of serum etonogestrel concentration are acceptable pharmacokinetic outcomes for etonogestrel implant studies.

Implications: Pharmacokinetic studies of the etonogestrel contraceptive implant assume single-time measurements are stable steady-state estimates based on small studies using older analysis methods. Our repeated measures study using modern liquid-chromatography mass-spectrometry analysis methods provides updated support for single-time pharmacokinetic measurements among etonogestrel implant users.

Trial registration: ClinicalTrials.gov NCT03092037.

Keywords: Contraceptive implant; Etonogestrel; Pharmacokinetics; Repeated measures; Variability.

Conflict of interest statement

Financial Disclosure: Dr. Teal serves on a Data Monitoring Board for a study funded by Merck and Co and has served as a consultant for Bayer Healthcare. The University of Colorado Department of Obstetrics and Gynecology has received research funding from Bayer, Agile Therapeutics, Merck and Co, and Medicines360. The other authors did not report any potential conflicts of interest.

Copyright © 2021. Published by Elsevier Inc.

Figures

Figure 1:

Scatterplot of initial serum etonogestrel (ENG) concentrations from 20 contraceptive implant users and the corresponding percent differences between their initial serum ENG concentrations and one-week and two-week repeat measurements. Line of best fit included (black line) with R2=0.03.