Oxybutynin for Androgen Deprivation–Associated Hot Flashes in Prostate Cancer
In a letter to the editor of The New England Journal of Medicine, Smith et al describe successful use of oxybutynin to treat hot flashes in a patient receiving androgen-deprivation therapy (ADT) for prostate cancer. As noted by the authors, nonhormonal treatments for menopausal hot flashes in women generally have been found to have little efficacy in men receiving ADT for prostate cancer. Oxybutynin has been shown to be effective for refractory hot flashes in women, with one study showing improvement with the agent in 73% of women vs 26% with placebo.
ADT and Hot Flashes
In the case reported, a 65-year-old patient had a prostate-specific antigen–only recurrence detected after radical prostatectomy. He was receiving gabapentin 300 mg 3 times a day for neuropathic pain and continued on this treatment while starting neoadjuvant and concurrent treatment with depot leuprolide 22.5 mg every 3 months and bicalutamide 50 mg daily for 6 months, with radiotherapy scheduled to begin after 3 months.
After 2 weeks, the patient experienced an abrupt onset of drenching hot flashes that occurred every 20 to 30 minutes beginning at 2:30 AM every night, preventing the patient from sleeping. No relief was achieved with the addition of extended-release venlafaxine 75 mg or an increase in gabapentin dose to 900 mg at night (1,500 mg/d total) for more than 3 weeks.
Oxybutynin Treatment
The patient then started on oxybutynin 5 mg twice a day, which provided relief from the sweating within 2 hours of dosing and permitted the patient to sleep through the night. He continued to take oxybutynin 1.25 to 2.5 mg twice a day for 40 days, experiencing only transient hourly body warmth. Gabapentin and venlafaxine were tapered and stopped without recurrence of the hot flashes and sweating. The hot flashes resumed when the patient subsequently stopped oxybutynin due to insomnia, dry mouth, and restless leg syndrome. Restarting of oxybutynin 2.5 mg twice a day produced relief from hot flashes within hours. Insomnia was treated with intermittent zolpidem.
The authors concluded, “We hope that this case report of successful treatment of refractory hot flashes in a man undergoing androgen deprivation for treatment of prostate cancer will stimulate interest in the oxybutynin class of drugs for hot flashes in men.”
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