PRIOR CONCURRENT THERAPY: Biologic therapy: No prior ketoconazole Chemotherapy: No prior doxorubicin, vinblastine, estramustine, paclitaxel, or etoposide No greater than one prior cytotoxic therapy No other concurrent chemotherapy At least 8 weeks since prior mitomycin At least 60 days since prior suramin Endocrine therapy: No antiandrogen therapy such as flutamide or nilutamide within 4 weeks (6 weeks for bicalutamide) without response OR Progression since antiandrogen withdrawal Prior dexamethasone therapy discontinued Radiotherapy: At least 10 weeks since prior strontium Sr 89 and no more than 1 prior regimen No concurrent strontium Sr 89 Surgery: Not specified Other: No other concurrent therapy for prostate cancer No concurrent H2 blockers, omeprazole, or antacids No concurrent terfenadine and astemizole