Amenorrhea Rate with Myfembree
Myfembree (relugolix 40 mg/estradiol 1 mg/norethindrone acetate 0.5 mg) achieves amenorrhea in approximately 64-70% of women with uterine fibroids at 24 weeks, with rates increasing to 66-70% at 52 weeks of continuous treatment.
Evidence from Pivotal Trials and Real-World Data
The amenorrhea rates with Myfembree are consistently high across multiple studies:
Primary Clinical Trial Data
- At 24 weeks: In the pooled LIBERTY 1 and 2 trials, 64.9% of women with concomitant adenomyosis achieved amenorrhea 1, with similar rates in the overall fibroid population
- At 52 weeks: The LIBERTY Long-Term Extension study demonstrated amenorrhea in 70% of the overall population 2
- In Black/African American women: 64.3% achieved amenorrhea through 52 weeks of continuous treatment 3
Real-World Clinical Practice
Recent real-world evidence from routine gynecological practice confirms these trial findings:
- At 6 months: 52.7% amenorrhea rate
- At 12 months: 66% amenorrhea rate 4
The slightly lower real-world rates at 6 months likely reflect the heterogeneity of clinical practice settings and patient populations compared to controlled trial conditions.
Clinical Context and Mechanism
Myfembree works as a GnRH antagonist that suppresses the reproductive axis, reducing menstrual bleeding 5. The integrated add-back therapy (estradiol and norethindrone acetate) mitigates hypoestrogenic effects while maintaining efficacy for bleeding control 2.
Key clinical point: Amenorrhea rates are dose-dependent and time-dependent, with sustained treatment showing progressive improvement. The combination formulation allows for long-term use (up to 52 weeks demonstrated) with preserved bone mineral density 3.
Comparative Perspective
While the guidelines mention other GnRH antagonists like linzagolix (67-87% amenorrhea with add-back at 200 mg dose) 2, Myfembree's single-tablet formulation with integrated add-back therapy provides consistent amenorrhea rates of approximately two-thirds to three-quarters of treated women by 6-12 months of continuous use.
The amenorrhea endpoint is clinically meaningful as it correlates with resolution of heavy menstrual bleeding, improvement in anemia (59.1% of anemic women achieved >2 g/dL hemoglobin increase), and enhanced quality of life 3.