Levonorgestrel release rates measured through analysis of two-rod contraceptive explants

OBJECTIVE: The objective was to characterize and compare in vivo rates of levonorgestrel (LNG) release from Sino-implant (II) and Jadelle® contraceptive implants. STUDY DESIGN: We sampled 48 Sino-implant (II) and 49 Jadelle® explant sets for residual LNG content from participants treated for up to 51 months in a randomized contraceptive efficacy trial in the Dominican Republic (DR). Additional Sino-implant (II) explants were obtained from 8 women who became pregnant in the DR trial and 10 who contributed 3 to 5 years of use in a cohort study in China. Baseline LNG loads were estimated from five unused implant sets per device type. Release profiles were estimated using mixture models that captured initial burst fractions and compared with efficacy and pharmacokinetics data from the DR trial. RESULTS: Estimated baseline LNG loads for Sino-implant (II) and Jadelle® were 142.8 mg and 150.5 mg, respectively (vs. the labeled 150 mg). There was an initial burst release of drug (5.6% and 7.9%, respectively) followed by an exponential decrease in LNG content evident for each device. Release rates were significantly lower for Sino-implant (II) throughout the treatment period, with estimated rates after 3 years of 24.2 mcg/day and 29.0 mcg/day for Sino-implant (II) and Jadelle®, respectively. The estimated Sino-implant (II) rate after 3 years was similar to the predicted rate after 5 years (23.6 mcg/day) for Jadelle® (rate ratio: 1.03; 95% confidence interval: 0.92–1.13). CONCLUSIONS: Sino-implant (II) LNG release rates were significantly lower than Jadelle® with Sino-implant (II) rates through year 3 comparable to Jadelle® rates through year 5. These results reinforce the 3-year duration of action for which Sino-implant (II) was prequalified by the World Health Organization. IMPLICATIONS: This analysis confirms the WHO prequalification of Sino-implant (II) for 3 years of use and supports different durations of action for Jadelle® and Sino-implant (II). It provides additional evidence that this approach can complement efficacy trials in determining duration of action of hormonal contraceptives in general.