Phase III, randomised, double-blind, placebo-controlled study of the β3-adrenoceptor agonist mirabegron, 50 mg once daily, in Japanese patients with overactive bladder.

Objective: To evaluate the efficacy and safety of the β3-adrenoceptor agonist mirabegron, in a Japanese population with overactive bladder (OAB).

Patients And Methods: This randomised, double-blind, placebo-controlled phase III study enrolled adult patients experiencing OAB symptoms for ≥24 weeks. Patients with ≥ 8 micturitions/24 h and ≥1 urgency episode/24 h or ≥1 urgency incontinence episode/24 h were randomised to once-daily placebo, mirabegron 50 mg or tolterodine 4 mg (as an active comparator, without testing for non-inferiority of efficacy and safety) for 12 weeks. The primary endpoint was the change in the mean number of micturitions/24 h from baseline to final assessment. Secondary endpoints included micturition variables related to urgency and/or incontinence and quality-of-life domain scores on the King's Health Questionnaire. Safety assessments included adverse events (AEs), post-void residual urine volume, laboratory variables, vital signs and 12-lead electrocardiogram.

Results: A total of 1139 patients were randomised to receive placebo (n = 381), mirabegron 50 mg (n = 380) or tolterodine 4 mg (n = 378). Demographic and baseline characteristics were similar among the treatment groups. At final assessment, mirabegron was significantly superior to placebo in terms of mean [sd] change from baseline in number of micturitions/24 h (-1.67 [2.212] vs -0.86 [2.354]; P < 0.001) and mean [sd] change from baseline in number of urgency episodes/24 h (-1.85 [2.555] vs -1.37 [3.191]; P = 0.025), incontinence episodes/24 h (-1.12 [1.475] vs -0.66 [1.861]; P = 0.003), urgency incontinence episodes/24 h (-1.01 [1.338] vs -0.60 [1.745]; P = 0.008), and volume voided/micturition (24.300 [35.4767] vs 9.715 [29.0864] mL; P < 0.001). The incidence of AEs in the mirabegron group was similar to that in the placebo group. Most AEs were mild and none were severe.

Conclusions: Mirabegron 50 mg once daily is an effective treatment for OAB symptoms, with a low occurrence of side effects in a Japanese population.