Levonorgestrel concentrations during 7 years of continuous use of Jadelle contraceptive implants

Serum levonorgestrel concentrations were assayed in a multicenter, 7-year s tudy of 199 users of Jadelle rod implants. We examined drug levels, pattern s of changes, factors affecting drug levels, and concentrations at which pr egnancies occurred. Mean levonorgestrel concentrations declined from 435 pg /mL at 1 month of use to 64% of that value (280 pg/mL) at the end of 3 year s. Between the end of the third and fifth years neither mean nor median ser um levels varied markedly. At 5 years the mean concentration was again 64% of the first month's mean. Declining levels were observed thereafter throug h the end of 7 years when the mean, 224 pg/mL, was 52% of the 1-month value . Last measured drug concentrations of women who became pregnant during Jad elle use had mean and median values of 152 and 144 pg/mL, respectively, and a maximum value of 180 pg/mL. Analyses indicated ponderal index, body weig ht, duration of use, and a single clinical center were the most important v ariables affecting measured levonorgestrel levels. Approximately one-third of assays in the sixth and seventh years were found to be below 180 pg/mL, suggesting that Jadelle levonorgestrel implants would not maintain sufficie ntly high levels of effectiveness against pregnancy after 5 years and that heavier women would then be at greater risk of pregnancy. (C) 2001 Elsevier Science Inc. All rights reserved.