Recommended dose of flutamide with LH-RH agonist therapy in patients with advanced prostate cancer

In a recent study by the Casodex Combination Study Group, USA, patients in a flutamide (750 mg/day) plus LH-RH agonist group showed a high treatment failure rate, mainly due to flutamide-induced diarrhea and hepatotoxicity. Our current study was conducted to determine the optimal dose of flutamide for use in this type of combination therapy.

In a randomized, multicenter study, 30 patients (hormone untreated; stage C or D) were divided into 2 groups: flutamide 250 mg (125 mg x 2; 14 patients) and flutamide 375 mg (125 mg x 3; 16 patients, and each dose combined with either goserelin acetate (3.6 mg every 4 weeks) or leuprolide acetate (3.75 mg every 4 weeks). Goserelin and leuprolide were administered to patients in a 1:1 ratio. Flutamide monotherapy at a daily dose of 375 mg was determined to be the optimal dose in Japan in our previous phase II study. The endpoints of this pilot study were the objective response and adverse events during the 12-week treatment.

The objective response rate was 83.3% in the flutamide 250 mg group and 85.7% in the flutamide 175 mg group according to the Japanese response criteria for prostate cancer. Elevated PSA levels fell to within the normal range in 83.3% of the patients in the former group and in 93.3% of the patients in the latter group. One patient administered 250 mg of flutamide experienced diarrhea, while the serum GOT and/or GPT were elevated in 3 patients administered 250 mg of flutamide and 4 patients administered 375 mg of flutamide.

Based on the findings of this pilot study of maximal androgen-depletion therapy for advanced prostate cancer, 375 mg/day of flutamide is recommended in combination with an LH-RH agonist. Assessment of the effects of our recommended regimen on longer term survival, quality of life and antiandrogen withdrawal syndrome of patients treated requires additional patients and time for follow-up.