Ulipristal acetate is an oral medicine developed by Allergan to treat abnormal bleeding in women with uterine fibroids. 

Ulipristal acetate is approved in Europe and the U.K. (marketed under the brand name Esmya), as well as in Canada (brand name, Fibristal),  as a pre-operative and intermittent treatment of the moderate to severe symptoms of uterine fibroids. It may be used off label in some cases to treat endometriosis.

Ulipristal acetate is not approved by the U.S. Food and Drug Administration (FDA). Allergan submitted a request, in the form of a new drug application (NDA), to the FDA in October 2017, but that request was denied in August 2018, largely based on concerns elsewhere about instances of liver damage reported by women using this medicine. These reports originated in Europe and were investigated by the European Medicines Agency. 

Health authorities in Europe and Canada now advise that Esmya/Fibristal not be given to women with known liver problems, and require that liver tests be given to patients before, during, and after treatment use.

How ulipristal acetate works

Ulipristal acetate is a selective progesterone receptor modulator (SPRM). It works by blocking the effects of the hormone progesterone in specific tissues — in this case, the endometrium or the lining of the uterus, the pituitary gland, and uterine fibroid tissues.

Progesterone plays an important role in the development and growth of uterine fibroids. These fibroids, also known as leiomyomas or myomas, are non-cancerous growths of uterine tissue. Scientists think that fibroids occur when a muscle stem cell in the wall of the uterus divides more than it should, creating a mass of cells. Fibroid tissues contain more receptors for estrogen and progesterone than the normal uterine tissues. This means that fibroids are highly sensitive to these hormones.

Endometriosis occurs when endometrial cells grow in places other than the uterus. In the uterus, the endometrium grows and becomes thicker during a woman’s monthly cycle and then the cells are broken down and leave the body during menstruation. In endometriosis, the broken-down cells do not have a path to exit the body, causing inflammation and pain.

By blocking the action of progesterone in fibroid tissues and the endometrium, ulipristal acetate reduces their growth and may even shrink them. This, in turn, can ease the heavy and prolonged menstrual bleeding and pelvic pain that mark these conditions. Ulipristal acetate inhibits ovulation in most patients, which might prevent the buildup and breakdown of the endometrium.

Ulipristal acetate in clinical trials

Two Phase 3 clinical trials in the U.S., called VENUS 1 (NCT02147197) and VENUS 2 (NCT02147158), investigated the efficacy and safety of ulipristal acetate in treating abnormal bleeding associated with uterine fibroids. These trials demonstrated that, compared to placebo, ulipristal acetate eased the heavy bleeding and disruption of everyday life caused by uterine fibroids. These benefits were also seen in African-American and obese women, two patient groups at particularly high risk of developing uterine fibroids.

Four Phase 3 trials (NCT01642472, NCT01252069, NCT01156857, and NCT01629563) were conducted in Europe. Results of these studies, called PEARL I, II, III and IV,  found patients treated with ulipristal acetate had lesser bleeding and a higher rate of amenorrhoea, or the lack of a menstrual period, compared to those given placebo. A reduction in the size of uterine fibroids in treated patients was also reported.

A Phase 4 pilot study (NCT02213081) investigating ulipristal’s effectiveness in relieving pelvic pain caused by endometriosis was sponsored by Northwestern University and planned to enroll 25 women. This trial, with participants receiving ulipristal every other day for three months, was scheduled to close in June 2018 and its status is not known. A case study of a 25-year-old woman with endometriosis-related pain that could not be treated by surgery or other medications was published by the same researchers in 2017. It reported that 15 mg of ulipristal every other day for three months effectively treated her pain and induced amenorrhoea.


Last updated: August 5, 2019


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