Purpose: We compared the endocrinological and biochemical efficacy of abarelix depot, a gonadotropin-releasing hormone antagonist, with that of a widely used combination of luteinizing hormone releasing hormone agonist and a nonsteroidal antiandrogen.
Materials and methods: A total of 255 patients were randomized to receive open label 100 mg. abarelix depot or 7.5 mg. leuprolide acetate intramuscularly injection on days 1, 29, 57, 85, 113 and 141 for 24 weeks. Patients in the abarelix group received an additional injection on day 15 and those in the leuprolide acetate group received 50 mg. bicalutamide daily. Patients could continue treatment with study drug for an additional 28 weeks. The efficacy end points were the comparative rates of avoidance of testosterone surge (greater than 10% increase) within 7 days of the first injection and the rapidity of achieving reduction of serum testosterone to castrate levels (50 ng./dl. or less) on day 8. Patients were monitored for adverse events and laboratory abnormalities.
Results: Abarelix was more effective in avoidance of testosterone surge (p <0.001) and the rapidity of reduction of testosterone to castrate levels on day 8 (p <0.001) than combination therapy. No significant difference was seen between the groups in the initial rate of decline of serum prostate specific antigen or the ability to achieve and maintain castrate levels of testosterone. No unusual or unexpected adverse events were reported.
Conclusions: Abarelix as monotherapy achieves medical castration significantly more rapidly than combination therapy and avoids the testosterone surge characteristic of agonist therapy. Both treatments were equally effective in reducing serum prostate specific antigen, and achieving and maintaining castrate levels of testosterone.