PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: No prior systemic chemotherapy for metastatic prostate cancer (except neoadjuvant treatment for localized prostate cancer) Endocrine therapy: No prior systemic hormonal therapy for prostate cancer (except neoadjuvant treatment for localized prostate cancer) Radiotherapy: See Disease Characteristics Surgery: See Disease Characteristics Other: No other concurrent systemic therapy for metastatic prostate cancer At least 30 days since other prior investigational drugs No concurrent digoxin At least 7 days since prior thiazide diuretic therapy No concurrent magnesium containing antacids, bile resin binding drugs, or calcium supplements