Watson Pharmaceuticals announced that it has received approval from the FDA for its new six-month intramuscular formulation, Trelstar, a (triptorelin pamoate for injectable suspension) 22.5 mg. Trelstar 22.5 mg is a gonadotropin releasing hormone (GnRH) agonist used for the palliative treatment of advanced prostate cancer. It interrupts the production of testosterone to stem to growth of prostate cancer cells.
According to the information presented to the FDA, this new formulation maintains a mean testosterone levels similar those achieved with surgical castration. Trelstar 22.5 mg is expected to launch in this month according to representatives of Watson.
Trelstar 22.5 mg is designed to suppress testosterone for six months, it is now the only 6 month approved formulation. Trelstar was first approved in the United States in 2000 and is currently available in one-month (3.75 mg) and three-month (11.25 mg) formulations.
The approval is based on a 12-month phase III study. During the study, Trelstar 22.5 mg produced a mean testosterone serum level of 12.8 ng/dL from month 2 through month 12, well below castration levels associated with androgen deprivation therapy. They also reported that median PSA levels were reduced by 96.4% at the end of the study.
Reported side effects are similar to all of the other GnRH agonist currently used. Common reported adverse events associated with the use of the product included hot flushes (71.7% of subjects), erectile dysfunction (10%) and testicular atrophy (7.5%). There were also limited injection site reactions reported.
Men with micro metastatic and metastatic disease should not allow 6 months to go by between PSA tests. If you do receive one of the new 6 month injections of Trelstar make sure that you also get a prescription for a PSA test at least every three months or less if appropriate. If you see an increase in your PSA call your doctor and discuss it, don’t wait for your next appointment.
Joel T Nowak, MA, MSW