Elagolix (ABT–620) is a therapy that Neurocrine Biosciences and AbbVie are developing to treat menstrual and non-menstrual pelvic pain in women with endometriosis.

It is an antagonist of the gonadotropin-releasing hormone (GnRH). This means it inhibits GnRH’s ability to produce other hormones, including estrogen, which promotes endometriosis.

Neurocine Biosciences and Abbvie are also assessing Elagolix’s effect in patients with uterine scarring.

What is endometriosis?

Endometriosis involves endometrial cells, which normally line the inside of the uterus, growing outside the womb. The inflammation this triggers causes pelvic pain.

Endometrial cells grow inside the uterus to accommodate a baby in the event a woman becomes pregnant. If she does not become pregnant, endometrial cells detach from the walls of the uterus and are discharged during menstruation. The growth and detachment of the endometrium are regulated by a complex system of hormones that operate during the menstrual cycle.

Hormones are molecules that are produced in one part of the body but act in a location different from where they were made. In the case of the menstrual cycle, hormones are produced in two main organs: the brain and the ovaries. The hormones produced in the brain stimulate the production of ovarian hormones which, in turn, activate the growth of the uterus’ endometrial cells. GnRH is the hormone that plays the most crucial role in regulating the menstrual cycle.

How does Elagolix work?

Elagolix blocks hormone receptors that GnRH binds to. This means it inhibits the hormone’s effect on the production of ovarian hormones. Elagolix stops the abnormal growth of endometrial cells in women with endometriosis, decreasing inflammation and relieving pain.

Elagolix studies in endometriosis

Researchers have concluded  a Phase 3 clinical trial of Elagolix for the treatment of endometriosis-associated pain (NCT01931670). The randomized, parallel, double-blind, placebo-controlled trial assessed two doses of Elagolix — 150 mg once daily and 200 mg twice daily — over six months in 872 women in the United States and a number of other countries.

The study assessed changes in daily non-menstrual pelvic pain and daily menstrual cramps before treatment, and three and six months after treatment began. Both doses reduced non-menstrual pelvic pain and menstrual cramps associated with endometriosis at three and six months of treatment.

AbbVie plans to file a New Drug Application with the U.S. Food and Drug Administration in 2017 for Elagolix as an endometriosis treatment. The hope is the FDA will approve the drug in 2018.

Elagolix studies in uterine fibroids

Other clinical trials have evaluated Elagolix as a treatment for heavy bleeding due to uterine fibroids, or scarring. AbbVie addressed the results of a Phase 2b clinical trial in a press release in April 2017. Dr. James A. Simon, clinical professor of obstetrics and gynecology at George Washington University, and medical director at Women’s Health & Research Consultants in Washington, said: “Elagolix was well tolerated and has the potential to be an important treatment option for women suffering from heavy menstrual bleeding associated with uterine fibroids.”

Dr. Rob Scott, a vice president of AbbVie, added: “The positive results from this clinical trial represent a significant milestone in the development of Elagolix, support AbbVie’s ongoing Phase 3 uterine fibroids research, and demonstrate our continued commitment to address complex and serious diseases.”

A Phase 3 clinical trial (NCT02654054) that began in 2016 aims to enroll 400 women with heavy menstrual bleeding due to uterine fibroids. It will compare the percentage of women with a reduction in uterine blood flow before treatment and six months after treatment began. Alkaline hematin levels will be used to measure menstrual blood loss.

Other details about Elagolix

Estrogen is one of the hormones produced in the ovaries. Besides stimulating endometrial cell growth, it is fundamental to bone growth. Other GnRH antagonist drugs lead to bone density loss because they reduce estrogen levels. Because Elagolix has less impact on estrogen levels than other GnRH antagonists, it also has less effect on bone growth.

Elagolix can lead to infertility due to the menstrual-cycle changes it causes. Other common adverse events associated with its use include hot flashes, headaches, nausea, and fatigue. While most adverse events were similar across groups getting different doses of Elagolix, some, such as hot flashes and bone mineral density loss, were dose-dependent.

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