A phase II dose-ranging study of mirabegron in patients with OAB
Reviewed by Ann Crump

This was a multinational, multicentre, randomised, double–blind, double-dummy, parallel group placebo- and active- controlled phase II study. The study enrolled 1108 men and women aged 18 and over. The criteria were: patients must have had overactive blader (OAB) symptoms for ≥ three months with a frequency of micturitions ≥ eight times per 24 hours and at least three episodes of urgency over three days. Patients were initially started on a two-week placebo run-in period followed by a 12-week double-blind treatment period. Patients were randomised to receive either mirabegron at a dose of 25, 50, 100 or 200mg, placebo or tolterodine ER 4mg. Patients were required to attend six times during the study. Patients were assessed for their urinary symptoms by means of a micturitions diary, Patient’s Perception of Intensity of Urgency Scale and the ICIQ-OAB QOL questionnaires. Patients were also assessed with blood pressure, heart rate and electrocardiogram monitoring. The primary endpoint was the change in mean number of micturitions in 24 hours. Secondary endpoints, including urgency episodes, and safety endpoints, including changes in ECG parameters, were also recorded. Results showed a reduction in micturition frequency in the mirabegron group compared to the placebo which was statistically significant in the 50, 100 and 200mg group. The improvement seen in the 50, 100 and 200mg groups was effectively the same. The 100 and 200mg showed a significant increase in heart rate but there did not appear to be an increase in cardiovascular adverse events. ‘Responders’ according to patient perception ranged from 50-70.8% in the mirabegron group, 51% in the placebo group and 55% in patients taking tolterodine. The conclusion of the study was that the efficacy and tolerability of mirabegron in OAB patients was satisfactory compared to current antimuscarinics and therefore it has moved on to a phase III trial. 

A phase II dose-ranging study of mirabegron in patients with overactive bladder.
Chapple CR, Dvorak V, Radziszewski P, et al; on behalf of the Dragon Investigator Group.
INTERNATIONAL UROGYNECOLOGY JOURNAL
2013;24:1447-58.