Arimidex (anastrozole) is a breast cancer treatment, developed by AstraZeneca, that may also be used in combination with other therapies to treat pain caused by endometriosis.

How Arimidex works

Endometriosis is characterized by the growth of endometrial tissue (tissue that lines the uterus) in patches outside of the uterus, usually in other areas of the abdomen, forming lesions. These endometrial lesions swell and shed with the menstrual cycle, just like the normal endometrium, but lack an exit route to leave the body. This causes pain, inflammation, and infertility.

Arimidex is an aromatase inhibitor, meaning it works by blocking an enzyme called aromatase that is responsible for a critical step in the synthesis of estrogen, a hormone that controls the menstrual cycle.

Arimidex binds to aromatase enzymes and prevents them from making estrogen. This reduces the amount of estrogen present and, in essence, chemically induces menopause. Without estrogen, the endometrial lesions shrink and become less painful.

Arimidex in clinical trials for endometriosis

A Phase 4 clinical trial (NCT00286351) in Denmark examined whether a combination of Arimidex and Zoladex (a GnRH agonist) can work to shrink endometrial lesions and increase a patient’s chance of a success in vitro fertilization (IVF) and pregnancy. During the trial, 20 infertile women were treated with the combined therapy for 10 weeks, then their endometrial lesions were measured to record changes in size. The results, published in the European Journal of Obstetrics & Gynecology and Reproductive Biology, showed that the treatment significantly reduced the volume of endometrial lesions and was compatible with IVF pregnancy and delivery. However, many of the pregnancies were unsuccessful: of the nine women who conceived, three gave birth to healthy children.

A Phase 1 clinical trial (NCT02545452) investigated the pharmacokinetic interactions (how a drug behaves in the body) between an intravaginal ring releasing anastrozole and levonorgestrel, and a vaginally-administered antifungal treatment (miconazole), an antibiotic (clindamycin), a spermicide (nonoxynol-9), or the concomitant use of tampons. A total of 52 healthy volunteers were given anastrozole and levonorgestrel as a vaginal insert. Volunteers were then randomly assigned to treatment groups given miconazole, clindamycin, nonoxynol-9, or tampons for three days.

Results were published in the Journal of Clinical Pharmacology and showed no pharmacokinetic interactions between anastrozole/levonorgestrel and the tested antibiotic, antimycotic, spermicide, or tampons. The researchers concluded that no restrictions need to be placed on the use of intravaginal rings intended to treat the symptoms of endometriosis.

A Phase 4 clinical trial (NCT01769781) in Italy tested Arimidex plus Lupron, compared to Lupron alone, in treating women with recurrent endometriosis. A total of 70 patients were randomly assigned to receive either Arimidex plus Lupron, or Lupron alone, for three months. Its primary outcome was the extent of time patients experienced pain relief without disease recurrence. This trial was expected to conclude in July 2015, but results have not yet been published.

Other information

Arimidex may cause side effects that include blurred vision, nausea, headache, a slow or fast heartbeat, and swelling in the feet or legs.

Women taking aromatase inhibitors should also be taking an oral contraceptive or a GnRH receptor agonist to prevent the development of ovarian cysts. Patients may also be advised to take a calcium supplement, vitamin D, and bisphosphonate to reduce the risk of bone loss.


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