Urinary symptoms, including overactive bladder (OAB), are seen in up to 88% of Parkinson disease (PD) patients. Most anti-spasmodics for OAB are anticholinergic, which may worsen cognition and constipation in PD. Mirabegron, approved for OAB in the general population, has a novel mechanism of action, so it may avoid anticholinergic side effects in PD patients but there has not been a previously published prospective study of mirabegron in PD.

Thirty-one patients with PD and OAB were randomized 1:1 into placebo and treatment arms of this prospective, double-blind, placebo-controlled 10-week study.   

All patients received pelvic floor exercise (PFE) training. Patients in the control arm received placebo while treatment arm received mirabegron 25 mg with optional up-titration to 50 mg.

The primary outcome measure was the change in OAB Symptom Composite Score (OAB-SCS), which assesses voiding frequency and urgency. Secondary measures included number and volume of micturition, incontinence episodes, and patient assessments of OAB severity.

No statistically significant difference was seen between OAB-SCS changes in the placebo and treatment arms.

Patients receiving treatment showed statistically significant improvement in micturition volume between baseline and study midpoint but this was not maintained at study end. Trends suggesting treatment-related improvement in other secondary measures were seen, though these did not achieve statistical significance.

There were a limited number of adverse events not related to study drug.