Mirabegron is the first β3-adrenoceptor agonist used in clinical practice. In the USA and Canada, the recommended starting dose is 25 mg once daily, with an option to increase the dose to 50 mg. However, in Europe and Japan, the recommended initial dose is 50 mg once daily, with the 25-mg dose reserved for special populations (e.g. those with renal or hepatic impairment). In Taiwan, the recommended starting dose is 25 mg once daily, with an option to increase it to 50 mg, which is similar to the guidelines in the USA and Canada, but different from that of Japan. Less study investigate the additive efficacy of mirabegron dose escalation from 25 mg to 50 mg in Asian patients. We investigated the additive efficacy of mirabegron 50 mg and tried to find patients with higher satisfaction with dose escalation.

Patients aged ≥ 20 years with OAB symptoms receiving mirabegron 25 mg once daily were enrolled. The dose of mirabegron was escalated to 50 mg in all patients. Results were assessed using OAB symptom score (OAB-SS), patient perception of intensity of urgency scale (PPIUS), international prostate symptom score (IPSS) total, voiding (IPSS-V) and storage subscore (IPSS-S), patient perception of bladder condition (PPBC), and quality-of-life index (QoL-I) before and 3 months after dose escalation. The maximum flow rate (Qmax), voided volume and post-void residual (PVR) volume were also measured. Patients rated their symptoms as compared to that before dose escalation by using a validated global response assessment (GRA) scale, which comprises of 7 points, from markedly worse (-3) to markedly improved (+3). Satisfactory treatment results was considered if patients reported GRA≥1. Baseline parameters and parameters changed were compared between those with GRA≥2 and GRA<2.

A total of 124 patients (29 female and 95 male; mean age, 67 years) with OAB were enrolled. Seventy-five percent of patients had GRA≥1 after dose escalation to 50 mg. The OAB-SS, PPBC and QoL-I also improved significantly (Table 1). Six patients developed adverse events (AEs) include hypertension, constipation, dysuria, dry mouth and leg edema. All AEs were mild and tolerable, but one patient had urinary retention after dose escalation. Patients with PPIUS≥3 before dose escalation had significantly more improvement of urgency and storage symptoms than those with PPIUS<3. The decreased of PPRB and QoL-I was also more significant in patients with PPIUS≥3. Patients with GRA≥2 had significantly more reduction of urgency and storage symptoms.

Mirabegron dose escalation from 25 mg to 50 mg in Asian patients is safe and feasible. The storage symptoms improved and only 1 elder man developed urinary retention after dose escalation. Patients with more severe urgency under 25 mg mirabegron benefited more form dose escalation. We had reported a higher urgency scale was strongly associated with urodynamic detrusor overactivity (DO). Dose escalation from 25 mg to 50 mg seems helpful for DO, and was suggested for those with severe urgency/urgency urinary incontinence (UUI) even 25 mg was used. In addition, those with more improvement of urgency and storage symptoms had higher satisfaction.

Mirabegron dose escalation from 25 mg to 50 mg in Asian patients is safe and feasible. Dose escalation was suggested for those with severe urgency or UUI even 25 mg was used. Patients with more improvement of urgency and storage symptoms had higher satisfaction.