RETRACTED: Pharmacokinetics of Implanon® - An integrated analysis (Retracted Article)

The aims of this paper were to present data on the pharmacokinetics, clearance, bioavailability, and in vive absorption of etonogestrel (ENG); to present the results of a longitudinal analysis of the plasma concentration-time curves of ENG; and to present the results of a cross-sectional analysis on the association of body weight with serum ENG concentrations. Implanon(R) had an absorption rate of almost 60 mu g/day after 3 months, which slowly decreased to 30 mu g/day at the end of 2 years. The bioavailability over this period of time was constant and close to 100%. The clearance remained around 7.5 L/h. With a bioavailability and clearance that remained constant, it was concluded that accumulation of ENG does not occur. After Implanon insertion, serum concentrations increased within 8 h to concentrations associated with ovulation inhibition. Maximum mean serum concentrations (C-max) amounted to 813 pg/mL and the time (t(max)) to reach C-max was 4 days. After reaching C-max ENG serum concentrations declined to about 196 pg/mL at the end of the first year, followed by a slow decline to 156 pg/mL at the end of the third year. After removal of Implanon, serum ENG concentrations declined to levels less than the detection limit of the assay (20 pg/mL) within 1 week. Lower body weight was associated with higher serum ENG concentrations. (C) 1998 Elsevier Science Inc. All rights reserved.