REDucing Hot FLASHes in Women Using Endocrine Therapy.

A Randomized Intrapatient Cross-over Study to Assess the Efficacy of Oxybutynin Versus Venlafaxine in Reducing Hot Flashes in Women Using Endocrine Therapy After Breast Cancer.

The goal of this randomized intrapatient cross-over study is to assess the efficacy of oxybutynin versus venlafaxine in reducing hot flashes in women using endocrine therapy after breast cancer.

The objectives it aims to answer are:

• To assess the efficacy of oxybutynin versus venlafaxine in reducing hot flashes in women using endocrine therapy after breast cancer
• To assess side effects of oxybutynin versus venlafaxine.
• To assess the personal preference of women for oxybutynin versus venlafaxine in reducing hot flashes.
• To assess quality of life of women when reducing hot flashes in women using endocrine therapy after breast cancer.

Participants will fill-out a patient diary during 15 weeks total on a daily basis and receive an (online) questionnaire three times total.

Researchers will compare two groups (venlafaxine group versus oxubutynine group) to assess its efficacy concerning hot flashes.

Inclusion Criteria:

• Pre-, peri- or postmenopausal women of 18 years or above;
• Indication for endocrine therapy and already started with tamoxifen, aromatase inhibitors or luteinizing hormone-releasing hormone analogues for at least 4 weeks and planning to continue for the duration of the study;
• Experiencing hot flashes with a minimum of 14 per week for at least 1 month and desire to start a pharmacologic intervention.

Exclusion Criteria:

• Pregnant;
• Breast feeding;
• Patients who receive chemotherapy or immunotherapy/HER2 antibodies within the prior 8 weeks, and patients scheduled for chemotherapy during the study period;
• Palliative setting;
• Use of venlafaxine or any other antidepressants, also including St. John's wort within the previous year;
• Creatinine clearance < 30 ml/min;
• Liver cirrhosis;
• Use of gabapentin and/or calcium channel antagonists within 2 weeks of study entry;
• Use of oxybutynin before study entry;
• Use of any other substances or therapies for the treatment of hot flashes, for instance acupuncture.