Degarelix, an injectable drug manufactured by Ferring Pharmaceuticals and still awaiting a trade name before it can hit the market, belongs to class of drugs known as gonadotropin-releasing hormone (GnRH) receptor antagonists. These drugs block the body’s production of testosterone, which slows prostate cancer growth.

The approval is based on encouraging results from a year-long phase III randomized clinical trial. The study showed that degarelix is as effective at suppressing testosterone as leuprolide, a commonly used drug that is also a GnRH agonist, and it appears to take effect much more quickly.

At the end of the year, nearly all of the patients on either drug showed testosterone levels comparable with surgical removal of the testes. However, 99% of the patients receiving degarelix reached these low testosterone levels after about 2 weeks of treatment, compared with only 18% of the patients receiving leuprolide.

Further, degarelix didn’t appear to cause the temporary surge in testosterone levels at the start of treatment, an effect commonly seen with other hormone therapies for prostate cancer known as GnRH agonists, including leuprolide.

Prostate-specific antigen (PSA) levels were also monitored during the trial. While PSA results are not always clear-cut, a high PSA level is usually a good indicator of the presence of prostate cancer. Patients receiving degarelix saw their PSA levels drop by an average of 64% 2 weeks after starting treatment, by 85% after 1 month, and by 95% after 3 months. PSA levels stayed low during the rest of the trial.

Commonly reported side effects included pain, redness, and swelling at the injection site; hot flashes; weight gain; fatigue; and increases in some liver enzyme levels.

Once a trade name is green-lighted by the FDA, degarelix will be the only GnRH antagonist available in the United States. (A similar drug, abarelix, was withdrawn from the US market several years ago.) Degarelix is also awaiting approval overseas.

For more information, see our Detailed Guide: Prostate Cancer, especially the section on Hormone Therapy.