An oral gonadotropin-releasing hormone receptor antagonist, linzagolix, significantly reduced uterine fibroid–associated heavy menstrual bleeding among women participating in the PRIMROSE I and II trials. The identical 52-week trials included 511 and 501 participants. They were randomized to 1 of 5 masked treatments that included linzagolix, placebo, and/or estradiol/norethisterone acetate add-back therapy.
Results showed: “In both trials, a significantly higher proportion of women had a reduction in heavy menstrual bleeding in all linzagolix (with or without add-back therapy) treatment groups compared with the placebo group (P≤0.003). In PRIMROSE 1, the response rates were 56.4% (95% CI 45.8–66.6%) in the 100 mg group, 66.4% (56.6–75.2%) in the 100 mg plus add-back therapy group, 71.4% (61.8–79.8%) in the 200 mg group, and 75.5% (66.0–83.5%) in the 200 mg plus add-back therapy group, compared with 35.0% (25.8–45.0%) in the placebo group. In PRIMROSE 2, the response rates were 56.7% (46.3–66.7%) in the 100 mg group, 77.2% (67.8–85.0%) in the 100 mg plus add-back therapy group, 77.7% (68.4–85.3%) in the 200 mg group, and 93.9% (87.1–97.7%) in the 200 mg plus add-back therapy group, compared with 29.4% (20.8–39.3%) with placebo. The most common adverse events up to 24 weeks were hot flushes (35% of participants in PRIMROSE 1 and 32% in PRIMROSE 2 with linzagolix [200 mg] alone and 3–14% in all other groups).”