San Antonio, TX, Dec. 10, 2018, -- Oxybutynin, a drug widely used to treat urinary incontinence caused by an overactive bladder, helps treat hot flashes in breast cancer survivors, new research shows.
It also helped patients who did not have breast cancer but who were bothered by frequent or severe menopausal symptoms, according to a presentation at the San Antonio Breast Cancer Symposium (SABCS) 2018.
"Hot flashes are a big problem across the general population, but breast cancer survivors are at higher risk for experiencing either more severe or longer-lasting hot flushes, often as a consequence of our therapies," said lead author Roberto Leon-Ferre, MD, an assistant professor of oncology at the Mayo Clinic in Rochester, MN.
Hot flashes can affect breast cancer outcomes -- symptoms can be so severe that patients will stop endocrine therapy early, he said.
In the new study, oxybutynin significantly made hot flashes less frequent and less severe, and its use had a positive impact on patient quality of life.
To qualify for the study, women had to be having 28 or more hot flashes a week for at least 30 days.
Nearly two-thirds of 150 patients enrolled in the trial took either the cancer drug tamoxifen or an aromatase inhibitor for breast cancer for the entire study. The remaining women were not breast cancer patients.
Almost half of the women in each group reported having 10 or more hot flashes a day, and more than three-quarters of them reported that their hot flashes had lasted for 9 months or longer.
Patients in the study received oxybutynin at a dosage of either 2.5 mg twice a day or 5 mg twice a day for 6 weeks.
The investigators also used a weekly "hot-flash diary" to find out how much hot flashes were interfering with a patient's life, Leon-Ferre said. About 50 patients were enrolled in each of the three treatment groups.
The investigators evaluated changes in patient symptoms over 6 weeks.
Leon-Ferre and colleagues saw that for women who received the 5 mg dose of oxybutynin, hot flash scores at week 6 were lessened by nearly 80%.
The 2.5-mg dose had a similar though slightly less pronounced effect on hot flash scores by the study’s end.
Patients taking a placebo, or fake treatment, reported a 30% drop in hot flash scores.
Women who received either of the two dosages of oxybutynin rated sleep, leisure activities, work, and relationships much better, compared with women who got the placebo.
But neither dose of oxybutynin offset the effect that hot flashes had on patients' ability to concentrate or on their sexuality. Side effects included dry mouth, abdominal pain, and difficulty urinating with both dosages.
The Mayo Clinic has long explored new therapies for hot flashes in women who cannot take hormone replacement therapy -- the most effective treatment for menopausal symptoms -- because they have either had breast cancer or are at high risk for it.
Kent Osborne, MD, co-director of SABCS and director of the Dan L. Duncan Comprehensive Cancer Center at the Baylor College of Medicine in Houston, said he is going to start using oxybutynin for more patients because it is at least as effective as venlafaxine and it has some advantages.
For example, oxybutynin does not interfere with tamoxifen, an important consideration for breast cancer survivors.
In contrast, it is thought that some antidepressants used to treat hot flashes can affect how well tamoxifen works.
"You have to pick the right patient," Osborne said. "If you have a patient with a lot of anxiety or depression, then you are going to use venlafaxine; if not, you might want to use oxybutynin."
The fact that some of the patients enrolled in the current study were already taking an antidepressant or other drugs presumably to treat their hot flashes suggests that these other medications were not fully working for them, Osborne said.
The study was supported by the Breast Cancer Research Foundation. Leon-Ferre has received travel support from Immunomedics. Osborne has received grant support from Puma Biotechnology and has served on the advisory board for Tolmar Pharmaceuticals and on a data monitoring committee for a clinical trial conducted by Lilly.