Myovant Sciences and Pfizer announce US FDA acceptance of supplemental NDA for Myfembree

Myovant Sciences and Pfizer announced today that the US Food and Drug Administration (FDA) accepted for review a supplemental New Drug Application (sNDA) for Myfembree (relugolix 40 mg, estradiol 1 mg, and norethindrone acetate 0.5 mg). The sNDA proposes updates to Myfembree’s US Prescribing Information (USPI) based on safety and efficacy data from the phase-III Liberty Randomised Withdrawal Study (RWS) of Myfembree in pre-menopausal women with heavy menstrual bleeding associated with uterine fibroids for up to two years. The FDA set a target action date of 29th January, 2023 for this sNDA under the Prescription Drug User Fee Act (PDUFA), Pfizer notified via a statement.

Patients who completed the 24-week pivotal Liberty 1 and 2 studies were offered the option to receive Myfembree for an additional 28 weeks in an open-label extension study. After completion of the Liberty 1 or Liberty 2 and the open-label extension studies, women who met the definition of responder (menstrual blood loss < 80 mL and a reduction from pivotal study baseline > 50 per cent) could participate in an additional 52-week randomised withdrawal study (N=229) designed to provide two-year safety and efficacy data on Myfembree and to evaluate the need for maintenance therapy. Women who entered the RWS were re-randomised to either Myfembree or placebo for 52 additional weeks (N = 229), with the primary endpoint at week 76. The Liberty randomised withdrawal study met its primary endpoint with 78.4 per cent of women who continued on Myfembree achieving the sustained responder rate (menstrual blood loss < 80 mL) through week 76 compared with 15.1 per cent of women who discontinued treatment and initiated placebo at week 52 (p < 0.0001). All three key secondary endpoints in the Liberty randomised withdrawal study were also achieved, including sustained responder rate through week 104, time to relapse of heavy menstrual bleeding, and amenorrhea rate (all p < 0.0001), the statement added.

The statement also said that bone mineral density remained stable in women who received Myfembree in the randomised withdrawal study. Additionally, bone mineral density was maintained through two years in the subset of women continuously treated with Myfembree (N = 31). The incidence of adverse events over one additional year of treatment was consistent with those observed in prior studies, with no new safety signals observed.

Myfembree was approved in the US in 2021 for the management of heavy menstrual bleeding associated with uterine fibroids in premenopausal women with a treatment duration of up to 24 months, the statement concluded.