Alliance A222001: A randomized, double-blind, placebo controlled phase II study of oxybutynin versus placebo for the treatment of hot flashes in men receiving androgen deprivation therapy.
Authors: Stish Brad J. , Mazza Gina L. , Nauseef Jones T. , Humeniuk Michael Sandon , Smith Thomas J. , Tofthagen Cindy , Diaz Pardo Dayssy Alexandra , Chay Christopher H. , Huang Andrew Jonathan , Naha Kushal , Tagawa Scott T. , Chow Selina Lai-ming , Adams-Campbell Lucile L. , Novotny Paul J. , Loprinzi Charles L. 
Published: June 2024

LBA12004 Background: Hot flashes are among the most common adverse events impacting quality of life reported by patients receiving androgen deprivation therapy (ADT) for the treatment of prostate cancer. Oxybutynin is an effective therapy for reducing frequency and severity of hot flashes in women. Pilot information supports that this drug may also benefit men with hot flashes related to ADT. Methods: Patients with prostate cancer receiving a stable regimen of ADT with at least 28 hot flashes per week were randomized to receive either oral oxybutynin 2.5 mg twice a day, oxybutynin 5 mg twice a day, or matching placebo doses for 6 weeks. The primary endpoint was the change in patient-reported hot flash scores (determined by multiplying the number of hot flashes by the mean hot flash severity [grade 0: none, 1: mild, 2: moderate, 3: severe, and 4: very severe]) from baseline to 6 weeks, as measured by a daily hot flash diary. A total of 87 patients provided 76% power to reject the null hypothesis of no between-arm mean difference in hot flash score reduction from baseline to 6 weeks, when comparing each oxybutynin arm to the combined placebo arms. This was based on a two-sided contrast estimated from a generalized linear mixed model, α= 0.10, intraclass correlation of 0.50, population standardized mean difference of 0.50, and 10% missing data rate. Results: 88 patients were accrued between 10/28/21 and 12/02/23. Six patients cancelled before starting treatment and one was ineligible, leaving 81 analyzed patients with a median age of 68. Baseline characteristics were balanced between arms with patients reporting an average of 10.15 (SD = 5.55) hot flashes per day and an average daily hot flash score of 18.23 (SD = 13.48) at enrollment. On average, patients on the placebo arm, low dose oxybutynin arm, and high dose oxybutynin arm had reductions of 2.15, 4.77, and 6.89 hot flashes/day, respectively. Compared to placebo arm patients, high dose oxybutynin arm patients had a greater reduction in hot flashes/day (p < 0.001), as did low dose oxybutynin arm patients (p = 0.02). Daily hot flash scores for the same three protocol arms reduced by an average of 4.85, 9.94, and 13.95 points, respectively. Compared to placebo arm patients, high dose oxybutynin arm patients had a greater reduction in daily hot flash scores (p = 0.002), as did low dose oxybutynin arm patients (p = 0.07). No treatment-related grade 3+ adverse events occurred. The most commonly reported oxybutynin-related grade 2 adverse event was dry mouth. Conclusions: Oxybutynin is superior to a placebo for the management of hot flashes in men associated with androgen deprivation therapy and appears to be well tolerated. Support: UG1CA189823; https://acknowledgments.alliancefound.org . Clinical trial information: NCT04600336 .