Pharmacokinetics of two low-dose levonorgestrel-releasing intrauterine systems and effects on ovulation rate and cervical function: pooled analyses of phase II and III studies.

OBJECTIVE: To assess the pharmacokinetics and pharmacodynamics of levonorgestrel intrauterine system (LNG-IUS) 13.5 mg and LNG-IUS 19.5 mg (total content). DESIGN: Pooled pharmacokinetic and pharmacodynamic analyses of phase II and III studies. SETTING: Randomized, open-label, multicenter studies. PATIENT(S): Nulliparous and parous women. INTERVENTION(S): Levonorgestrel intrauterine system 13.5 mg, LNG-IUS 19.5 mg, or LNG-IUS 20 µg/24 h (total content 52 mg). MAIN OUTCOME MEASURE(S): Pharmacokinetics of LNG, ovulation rate, cervical function, and endometrium effects. RESULT(S): The in vivo LNG release rate of LNG-IUS 13.5 mg was approximately 14 µg/24 h after 24 days, declining progressively to 5 µg/24 h after 3 years. The average LNG serum concentration over 3 years of use was 74.3 ng/L, 114 ng/L, and 218 ng/L for LNG-IUS 13.5 mg, LNG-IUS 19.5 mg, and LNG-IUS 20 µg/24 h, respectively. All treatments showed very similar progestogenic effects on cervical mucus, with low and similar cervical scores throughout treatment. Ovulation was observed in the majority of women in all groups where assessment was possible, although there was a lower incidence of anovulation with LNG-IUS 13.5 mg and LNG-IUS 19.5 mg compared with LNG-IUS 20 µg/24 h. The progestogenic effect on the endometrium was marked in all three LNG-IUS groups. CONCLUSION(S): Levonorgestrel intrauterine system 13.5 mg and LNG-IUS 19.5 mg result in alower systemic exposure to LNG, lower incidence of anovulation, and similar progestin impact on the endometrium and cervical function compared with LNG-IUS 20 µg/24 h.