Fulvestrant (Faslodex)

How Fulvestrant (Faslodex) Works

Fulvestrant is a drug used as a type of hormone treatment in patients with breast cancer. It is defined as a “synthetic estrogen receptor antagonist” by the National Cancer Institute (NCI) Drug Dictionary. “Unlike tamoxifen (which has partial agonist effects) and the aromatase inhibitors (which reduce the estrogen available to tumor cells), fulvestrant binds competitively to estrogen receptors in breast cancer cells, resulting in estrogen receptor deformation and decreased estrogen binding. In vitro studies indicate that fulvestrant reversibly inhibits the growth of tamoxifen-resistant, estrogen-sensitive, human breast cancer cell lines.”

The growth of certain types of breast cancer is promoted by the female hormones estrogen and progesterone. These breast cancer types are known as hormone sensitive or hormone receptor positive, and in order to treat them, drugs like fulvestrant work by blocking the effects of estrogen and progesterone. In the specific case of fulvestrant, its mechanism of action is focused on stopping estrogen receptors in order to block the hormone from reaching the cells. Therefore, the drug is designed to slow down or stop breast cancer growth. Fulvestrant is administered in the form of two injections, each of them injected into a different buttock.

Fulvestrant (Faslodex) for Breast Cancer

Fulvestrant was approved by the U.S. Food and Drug Administration (FDA) in April 2002, and it is commercialized under the brand name Faslodex by AstraZeneca. The drug is indicated for the treatment of postmenopausal breast cancer female patients whose disease has progressed after receiving anti-estrogen therapy like tamoxifen. The treatment, which takes about one to two minutes, is usually given weekly for the first three doses and then monthly, and the injections are given by a doctor or nurse practitioner. The approval was based on the results from two randomized clinical trials that were conducted in North America and Europe that compared the effectiveness of fulvestrant with the aromatase inhibitor anastrozole.

In North America, the double-blind study included 400 women, and in Europe, the open and randomized study included 451 women. The research revealed that after treated with fulvestrant 250 mg intramuscularly once a month or anastrozole 1 mg orally once a day, all patients progressed after previous therapy with an anti-estrogen or progestin, which demonstrated that fulvestrant is at least as effective as anastrozole. Patients may, however, experience side effects from the treatment. The most common adverse events reported include vomiting, nausea, constipation, pain, headache, diarrhea, hot flushes, and pharyngitis (throat inflammation).

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