Trial evaluates contraceptive efficacy of Mirena Intrauterine System through 8 years

USA: Findings from the Mirena Extension trial have shown the high contraceptive efficacy, a favorable safety profile, and user satisfaction of 52-mg levonorgestrel-releasing intrauterine system (52-mg LNG-IUS) through 8 years of use. The findings were published in the American Journal of Obstetrics and Gynecology. 

A total of 26 post-treatment pregnancies were reported, of which 24 occurred in women who discontinued 52-mg LNG-IUS because of their wish for pregnancy. The bleeding pattern remained highly favorable in women who elected to continue use for eight years.

The 52-mg levonorgestrel-releasing intrauterine system is a long-acting contraceptive option with approval for its use for up to 7 years. The Mirena Extension Trial by Jeffrey T Jensen, Oregon Health & Science University, Portland, Oregon, USA, and colleagues evaluated the safety and efficacy of 52-mg LNG-IUS during extended use beyond 5 and 8 years.

The multicenter, single-arm study in the US enrolled existing users of 52-mg LNG-IUS for 4.5-5 years aged 18-35 years. The researchers assessed the contraceptive efficacy (Pearl Index) and the cumulative failure rate (using the Kaplan-Meier method) of 52-mg LNG-IUS during extended use. Bleeding outcomes and adverse events were also evaluated.

Two hundred forty-three entered, and 223 completed eight years of 52-mg LNG-IUS use out of 362 participants starting Year 6. Just over half the participants were parous. The mean age was 29.2 years, and all participants were ≤36 years at the end of Year 8.

The study demonstrated the following findings:

• Two pregnancies occurred during years 6 through 8 of Mirena IUS use, Both with the device in situ. The Year 6 pregnancy was of unknown location and resolved spontaneously.
• In Year 7, the pregnancy was ectopic and resolved with methotrexate treatment. The 52-mg LNG-IUS was removed in both cases, and the participants left the trial.
• For years 6-8, the 3-year Pearl Index was 0.28, with a 3-year cumulative failure rate of 0.68%.
• Pearl Indexes for Years 6, 7, and 8 were 0.34, 0.40, and 0.00.
• The Pearl Index for 3-year (6-8) ectopic pregnancy was 0.14.
• Treatment-emergent adverse events were found in 249/362 participants (68.8%), with 65 (18.0%) events considered related to the 52-mg LNG-IUS.
• The discontinuation rate was 38.4%, most commonly due to a wish for pregnancy (12.2%, 44/362).
• During extended use beyond five and up to 8 years, participants reported a decrease in the mean number of bleeding/spotting days, with approximately half of the women experiencing amenorrhea or irregular bleeding.
• The researchers did not enroll a sufficient number of women using 52-mg LNG-IUS for contraception and heavy menstrual bleeding to assess the indication's extended use.
• At the end of Year 8, most (98.7%) of the participants who completed the study remained satisfied with the continued use of 52-mg LNG-IUS.
• Of the 31 women who discontinued early due to wish for pregnancy with evaluable data for return-to-fertility analysis, 24 reported a post-treatment pregnancy within one year, giving a 12-month return-to-fertility rate of 77.4%.

The researchers conclude, "these findings support the continued use of 52-mg LNG-IUS for up to 8 years in women wishing to continue treatment."

Reference:

Jensen JT, Lukkari-Lax E, Schulze A, Wahdan Y, Serrani M, Kroll R. Contraceptive efficacy and safety of 52mg LNG-IUS for up to 8 years: findings from the Mirena Extension Trial. Am J Obstet Gynecol. 2022 Sep 9:S0002-9378(22)00729-3. doi: 10.1016/j.ajog.2022.09.007. Epub ahead of print. PMID: 36096186.