Watson Pharmaceuticals, Inc. announced that the U.S. Food and Drug Administration (FDA) has approved Trelstar – 22.5 mg (triptorelin pamoate for injectable suspension) at a dosage which will be required only to be administered twice a year.

In the phase III clinical trial, Trelstar demonstrated the every six-month dosing to be both safe and effective in the treatment of men for palliative treatment of advanced prostate cancer.

It is anticipated that the drug will become available for use in May 2010.

Trelstar is the only approved six-month intramuscular GnRH agonist (it surpresses testosterone production) available for the palliative treatment of advanced prostate cancer. Trelstar does not require refrigeration while it is stored.

It is administered via the MIXJECT® delivery system, which utilizes a thin (21-gauge) needle so there should not be a lot of discomfort or secondary injection site complications. In the clinical trial, only 1.7% of patients reported injection site pain.

The approval is based on a 12-month (48 week) phase 3 study evaluating its efficacy, pharmacokinetics, and safety. It was administered every six months (24 weeks) in men with advanced prostate cancer. Over the study, TRELSTAR® 22.5 mg produced a mean testosterone serum level of 12.8 ng/dL from month two through month 12, well below castration levels associated with androgen deprivation therapy. By day 29, 97.5% of the clinical trial patients achieved castrate level, and >98% of all patients were below castrate level at month six and month 12. Median prostate specific antigen (PSA) was also reduced by 96.4% at the end of the study.

The most commonly reported adverse events associated with the use of TRELSTAR® 22.5 mg included hot flushes (71.7%), erectile dysfunction (10.0%), and testicular atrophy (7.5%).

Additionally, Abbott has filed a similar application with the FDA requesting their approval of Abbott’s newly developed six-month 45-mg Formulation of Lupron(R) Depot. Lupron(R) Depot is Abbott’s GnRH agonist drug.

Joel T Nowak, MA, MSW