Poster abstracts

Objectives: To evaluate levonorgestrel plasma concentrations from 72 through 96 months in obese and non-obese women using a levonorgestrel 52 mg intrauterine system (IUS). Methods: Eligible women 16-45 years old received a levonorgestrel 52 mg IUS (LilettaⓇ) in a multicenter trial evaluating efficacy and safety for up to ten years. All participants began blood sampling every six months at month 36. Levonorgestrel levels were analyzed using liquid chromatography-tandem mass spectrometry with a lower limit of detection of 25 pg/mL. We compared levonorgestrel concentrations in obese and non-obese women at each time point from 72 through 96 months using an independent-samples t-test. Results: Average BMI in obese and non-obese sub-study participants with sampling at 60 months were 36.6±5.9 kg/m2 and 23.8±3.0 kg/m2, respectively; 24.4% of obese subjects had a BMI ≥40 kg/m2. Plasma levonorgestrel concentrations were lower in obese compared with non-obese subjects at all time-points: 68±31 pg/mL (n=80) vs. 103±44 pg/mL (n=163) at 72 months, 69±33 pg/mL (n=64) vs. 99±37 pg/mL (n=148) at 84 months, and 68±26 pg/mL (n=35) vs. 95±36 pg/mL (n=101) at 96 months (p<0.0001 for all months). Mean levonorgestrel concentrations declined slowly from 72 to 96 months in obese (0.4% decline) and non-obese (8% decline) users. Conclusions: Levonorgestrel plasma levels are low in all levonorgestrel 52 mg IUS users during the later effective years (years 6-8). Obese women demonstrate lower plasma levonorgestrel concentrations than non-obese women; the decline in all users was very gradual and remained parallel between obese and non-obese women from 72 to 96 months of use.