To compare mirabegron and vibegron as initial pharmacotherapy for overactive bladder (OAB) in elderly women.

We conducted a prospective, single-center, randomized, open-label trial including 131 postmenopausal women aged 70 years or older with OAB, allocated to mirabegron 50 mg (n = 64) or vibegron 50 mg (n = 67) once daily for 12 weeks (UMIN000038288). The primary endpoint was the change in total Overactive Bladder Symptom Score (OABSS) from baseline to week 12. Secondary endpoints included International Prostate Symptom Score (IPSS), King’s Health Questionnaire (KHQ), minimal clinically important change (MCIC; OABSS ≥3-point or KHQ ≥5-point reduction), and safety outcomes including treatment-related adverse events (TRAEs) and postvoid residual (PVR).

Baseline characteristics were similar between groups. Both treatments yielded significant within-group improvements. The adjusted between-group difference in OABSS change was −0.24 (95% CI, −1.12 to 0.64; p  = .59). MCIC rates were numerically higher with vibegron but not statistically different. TRAEs occurred in 22% and 32% of patients receiving mirabegron and vibegron, respectively ( p  = .24); most were mild (dry mouth, constipation). Serious events were rare and not considered drug-related.

Over 12 weeks, mirabegron and vibegron showed comparable efficacy and safety in pharmacotherapy-naïve elderly women with OAB. Given the single-center design and limited statistical power, these findings provide preliminary insights that may help guide the selection of first-line β3-adrenergic receptor agonists and highlight the need for larger multicenter trials.