Flutamide administration at 500 mg dialy has similar effects on serum testosterone to 750 mg daily

A prior comparison of 750 mg flutamide daily to 500 mg daily with an LHRH analog or orchiectomy showed no difference in effect on prostate specific antigen (PSA). However, any difference was likely masked by hypogonadism from concomitant LHRH analog or orchiectomy. We sought to evaluate different flutamide dosing schedules without this confounding factor. We recruited 50 men with advanced prostate cancer who elected to receive hormonal therapy to be randomized to 1 of 3 flutamide treatment groups: 1) 250 mg once daily, 2) 250 mg twice daily, or 3) 250 mg 3 times daily for 3 months, after which the therapy of their choice was instituted. Serum samples at the initiation of therapy and at the 1- and 3-month time point were assessed for PSA, testosterone, liver function tests, hematology, and renal function. Prostate volume, androgen deficiency symptoms, and a compliance diary were also recorded. Testosterone and PSA levels show a dose-dependent response to flutamide monotherapy. Loss of libido and erectile dysfunction occurred in all 3 treatment groups, with a trend toward worsening sexual function with higher flutamide dosing, but this trend did not reach statistical significance. Prostate volumes decreased by an average of 34.3% in the patients receiving 250 mg flutamide 3 times daily, 27.8% in patients receiving 250 mg flutamide twice daily, and 19.2% in those receiving a once daily dose of 250 mg flutamide. There was a significant difference between the once daily group and the 3 times daily group (P = .047). Flutamide at 500 mg did not result in significant changes in testosterone, PSA, prostate volume, or androgen deficiency symptoms compared to 750 mg daily after 3 months.