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

Ulipristal acetate is not yet approved by the U.S. Food and Drug Administration (FDA). But it is widely used in Europe and the U.K. (marketed under the brand name Esmya), as well as in Canada (brand name Fibristal), where it is approved as a pre-operative and intermittent treatment of moderate to severe symptoms of uterine fibroids.

How ulipristal acetate works

Ulipristal acetate is a selective progesterone receptor modulator (SPRM), which means that it blocks 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.

By blocking the action of progesterone in fibroid tissues, ulipristal acetate reduces their growth and may even shrink them. This, in turn, reduces heavy and prolonged menstrual bleeding. In addition, ulipristal acetate inhibits ovulation in most patients.

Ulipristal acetate in clinical trials

Allergan recently completed two U.S.-based Phase 3 clinical trials, called VENUS 1 (NCT02147197) and VENUS 2 (NCT02147158), that 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 reduced bleeding and the disruption of everyday life caused by uterine fibroids. African-American women and obese women are at a particularly high risk for uterine fibroids. The beneficial effects of ulipristal acetate in reducing bleeding and improving quality of life were also seen in this group of patients.

In addition to these two trials, four Phase 3 trials (NCT01642472NCT01252069, NCT01156857, and NCT01629563) were conducted in Europe where ulipristal acetate has been approved to treat uterine fibroids since 2012.

Other information

The FDA accepted a new drug application by Allergan for ulipristal acetate in October 2017 for the treatment of uterine fibroids. A decision on the approval of ulipristal in the U.S. is expected in the first half of 2018.


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