A low dose of oxybutynin, an anticholinergic used to treat incontinence associated with overactive bladder, reduces hot flashes and improves quality of life in breast-cancer survivors, according to a new study.
"This study, in addition to previously published work in this area, establishes that oxybutynin is an effective drug for treatment of hot flashes in patients who have relative or absolute contraindications to hormone-based therapy," lead investigator Dr. Roberto Leon-Ferre of Mayo Clinic, in Rochester, Minnesota, said in a statement from the San Antonio Breast Cancer Symposium (SABCS), where the study was presented December 7.
Small blue pills. Source: Getty
Breast-cancer survivors are at "higher risk for experiencing either more severe or longer lasting hot flashes, often as a consequence of our therapy," he added during a press briefing.
Participants in the randomized, double-blind, placebo-controlled trial included 150 women reporting at least 28 hot flashes per week over more than one month and who were seeking relief. About two-thirds of the women were on tamoxifen or an aromatase inhibitor during the study. Concurrent use of antidepressants, gabapentin, pregabalin were allowed, but not other anticholinergic medications.
The women were randomly assigned to take 2.5 mg of oxybutynin twice a day for six weeks (Oxy2.5); 2.5 mg twice a day for one week, with a subsequent increase to 5 mg twice a day (Oxy5); or placebo. The women reported the frequency and severity of hot flashes at baseline and monthly, and from this information, the researchers calculated a hot flash (HF) score.
Women on both oxybutynin doses experienced a decrease in their HF scores compared with the women on placebo. The mean change in HF score was -10.6 for women in the Oxy2.5 arm, compared with -5.7 with placebo. Women in the Oxy2.5 arm experienced an average of 4.8 fewer hot flashes per day, compared with 2.6 fewer hot flashes for the women in the placebo arm.
Women in the Oxy5 arm had a mean change in HF score of -16.9, and experienced an average of 7.5 fewer hot flashes per day.
Women in both oxybutynin arms reported improvement in work, social activities, leisure activities, sleep and overall quality of life.
"While the two oxybutynin doses were not formally compared, 5 mg twice daily appeared to be more effective," Dr. Leon-Ferre told the briefing.
"We were surprised by the rapidity of the response and the magnitude of the effect, considering the relatively low dose of the drug," he said in the release. "The fact that oxybutynin does not interfere with the metabolism of tamoxifen is an important consideration for breast cancer survivors, as some of the most effective non-hormonal treatments for hot flashes are thought to potentially decrease the efficacy of tamoxifen."
Side effects with oxybutynin were as expected with an anticholinergic and included constipation, dry mouth, diarrhea, difficulty urinating and episodes of confusion. All side effects were mild in severity and the rate of discontinuation of oxybutynin due to side effects was low for both arms.
One limitation of the study is that it did not address long-term toxicities of oxybutynin. Previous research has suggested that long-term use of anticholinergic drugs may be associated with cognitive decline. This should be further researched and taken into consideration when counseling patients, Dr. Leon-Ferre said.
The study was funded by the Breast Cancer Research Foundation. Dr. Leon-Ferre declared no conflicts of interest.
San Antonio Breast Cancer Symposium 2018.