A Safe Alternative to HRT?

By Jane Farrell

The drug oxybutynin works to reduce hot flashes in women, including breast cancer survivors who cannot take hormone replacement therapy, according to new research.

Oncologists Robert Leon-Ferre, M.D. and Charles Loprinzi, both of the Mayo Clinic, presented their findings at the 2018 San Antonio Breast Cancer Symposium.

Leon-Ferre said several factors contribute to the increased severity of hot flashes in breast cancer survivors: 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. “It is important for physicians to have effective options to treat hot flashes.” The drug is most commonly used to treat urinary incontinence.

In this study, researchers enrolled 150 women who had experienced at least 28 hot flashes per week over 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. The subjects were divided into three groups; those who had two different doses of oxybutynin and a third that got a placebo.

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

The long-term effects of oxybutynin still need to be studied.

“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,” Leon-Ferre said. “We were surprised by the rapidity of the response and the magnitude of the effect, considering the relatively low dose of the drug.” He says that oxybutynin does not interfere with the metabolism of tamoxifen. That’s important for breast cancer survivors, because the efficacy of tamoxifen has been affected by some other non-hormonal treatments.  (See our story, “American Heart Association: Some Breast Cancer Treatments May Increase Heart Disease Risk.”)

Leon-Ferre said that since oxybutynin is already available for other conditions, physicians could potentially prescribe it off-label. However, he says the study did not address long-term toxicities of oxybutynin. Previous research has indicated that 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.