Testing the Effects of Oxybutynin for the Treatment of Hot Flashes in Men Receiving Hormone Therapy for Prostate Cancer

The primary and secondary objectives of the study: PRIMARY OBJECTIVE: I. To assess the effects of two doses of oxybutynin chloride (oxybutynin) on hot flash scores relative to placebo. SECONDARY OBJECTIVES: I. To assess study accrual rates and compliance with the therapy. II. To characterize the safety and adverse event profile of two doses of oxybutynin in the study population. III. To evaluate the consistency of the results across the various methods used to evaluate the efficacy of oxybutynin (i.e., hot flash scores versus hot flash frequencies, mean differences versus 50% or greater reduction since baseline, single day versus full week to define patients' baseline hot flash scores). IV. To compare patient-reported quality of life and hot flash interference, as measured by the Hot Flash Related Daily Interference Scale (HFRDIS), across arms. V. To compare other changes in patient symptoms, as measured by the Symptom Experience Questionnaire, across arms. OUTLINE: Patients are randomized to 1 of 4 arms in a 2:2:1:1 ratio according to the dynamic allocation scheme. Experimental Arm (low dose): Patients receive low-dose oxybutynin chloride orally (PO) twice daily (BID) on days 8-49 (6 weeks) in the absence of unacceptable toxicity. Experimental Arm (high dose): Patients receive high-dose oxybutynin chloride PO BID on days 8-49 (6 weeks) in the absence of unacceptable toxicity. Placebo Arm (low dose): Patients receive low-dose placebo PO BID on days 8-49 (6 weeks). After 6 weeks, patients may cross over to Experimental Arm (low dose) per physician discretion. Placebo Arm (high dose): Patients receive high-dose placebo PO BID on days 8-49 (6 weeks). After 6 weeks, patients may cross over to Experimental Arm (high dose) per physician discretion. There will be a 6-week follow-up for the Placebo Arm patients who participate in the optional crossover phase.