SAN ANTONIO >> Research led by oncologists Dr. Roberto Leon-Ferre and Dr. Charles Loprinzi of the Mayo Clinic has found the drug oxybutynin helps to reduce the frequency and intensity of hot flashes in women who are unable to take hormone-replacement therapy, including breast cancer survivors.

The findings were presented at the 2018 San Antonio Breast Cancer Symposium earlier this month.

“Hot flashes are a common symptom of menopause and can be even more severe in breast cancer survivors than they are in the general population,” Leon-Ferre said.

Factors contributing to the increased severity of hot flashes in breast cancer survivors include exposure to chemotherapy, which may bring on early menopause; the use of antiestrogen drugs, such as tamoxifen or aromatase inhibitors; and the use of medications or procedures to suppress the function of the ovaries. Hormone-replacement therapy, which is sometimes used to treat hot flashes, is generally not recommended for breast cancer survivors.

“Hot flashes not only impact a patient’s quality of life, they are associated with patients prematurely discontinuing breast cancer treatment, which may increase the risk of breast cancer recurrence and mortality,” Leon-Ferre said.

Previous research had suggested hot flashes may be relieved with oxybutynin, an anticholinergic agent that interferes with the activity of a neurotransmitter in the brain and in the peripheral nervous system.

The drug is most commonly used to treat urinary incontinence. Leon-Ferre said since oxybutynin is already available for other indications, physicians could potentially prescribe it off-label. However, he noted the study did not address long-term toxicities of oxybutynin.

Previous research has indicated long-term use of this type of drug may be associated with cognitive decline. These possible side effects should be further researched and taken into consideration when physicians counsel patients.

Researchers sought to determine whether oxybutynin was more effective than placebo in treating hot flashes and in improving patients’ quality of life. The researchers enrolled 150 women who had experienced at least 28 hot flashes per week for more than a month, and who were bothered enough by them to want medication.

Sixty-two percent of the women were on tamoxifen or an aromatase inhibitor for the duration of the study. There were three groups in the trial with patients in two groups receiving different dosages of oxybutynin and patients in the third group receiving a placebo.

The study found patients on both oxybutynin doses saw a decrease in hot flashes compared to the women who took the placebo. The women in both oxybutynin groups also reported decreased interference of hot flashes in their work, social activities, leisure activities, sleep and improvement in their overall quality of life.

“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,” said Leon-Ferre.

“We were surprised by the rapidity of the response and the magnitude of the effect, considering the relatively low dose of the drug.” Leon-Ferre said oxybutynin does not interfere with the metabolism of tamoxifen, which is an important consideration for breast cancer survivors, as some of the most effective non-hormonal treatments for hot flashes (such as antidepressants) are thought to potentially decrease the efficacy of tamoxifen.