A Randomized Open-Label Study of Relugolix Alone or Relugolix Combination Therapy in Premenopausal Women.

ABSTRACT

BACKGROUND AND OBJECTIVE: Relugolix is a gonadotropin-releasing hormone receptor antagonist. Relugolix 40-mg monotherapy is associated with vasomotor symptoms and long-term bone mineral density loss due to hypoestrogenism. This study assessed whether the addition of estradiol (E2) 1 mg and norethindrone acetate (NETA) 0.5 mg to relugolix 40 mg (relugolix combination therapy) provides systemic E2 concentrations in the 20-50 pg/mL range to minimize these undesirable effects. METHODS: This was a randomized, open-label, parallel-group study to assess the pharmacokinetics, pharmacodynamics, safety, and tolerability of relugolix 40 mg alone or in combination with E2 1 mg and NETA 0.5 mg in healthy premenopausal women. Eligible women were randomized 11 to receive relugolix alone or relugolix plus E2/NETA for 6 weeks. Study assessments included pharmacokinetic parameters of E2, estrone, and relugolix in both treatment groups, and norethindrone in the relugolix plus E2/NETA treatment group at weeks 3 and 6. RESULTS: Median E2 24 h average concentrations with the relugolix plus E2/NETA group (N = 23) were 31.5 pg/mL, 26 pg/mL higher compared with the relugolix-alone group (6.2 pg/mL) (N = 25). There were 86.4% of participants in the relugolix plus E2/NETA group who had E2 average concentrations exceeding 20 pg/mL, the threshold expected to minimize bone mineral density loss, compared with 21.1% in the relugolix-alone group. Both treatments were generally safe and well tolerated. CONCLUSIONS: Relugolix 40 mg in combination with E2 1 mg and NETA 0.5 mg provided systemic E2 concentrations within a range expected to minimize the risk of undesirable effects of hypoestrogenism associated with the administration of relugolix alone. CLINICAL TRIAL REGISTRATION Clinicaltrials.gov identifier no. NCT04978688. Trial registration date 27 July, 2021; retrospectively registered.