Purpose To investigate the safety and efficacy of mirabegron for patients with overactive bladder (OAB) that is unresponsive to antimuscarinic agents or is related to benign prostatic hyperplasia (BPH). Methods Fifty-two newly diagnosed OAB patients (M group) and 45 patients with OAB that was unresponsive to antimuscarinics (S group) received mirabegron 50 mg once daily and were evaluated by OAB symptom score (OABSS), IPSS-QOL index, and IPSS at the time of baseline, 4 and 8 weeks. Newly diagnosed OAB patients treated with antimuscarinic agents were compared as controls. Results Mirabegron was effective for 85.2 % in M group. Significant improvements were seen in each domain of OABSS, and there was no significant difference with antimuscarinic therapy. Mirabegron was efficacious for 61.6 % of S group, and significant decreases of OABSS and IPSS-QOL index were observed. Significant improvements were also seen in voiding symptoms in men. Post-void residual urine volumes before and after treatment were 32.1 and 34.8 ml, and 26.2 and 31.3 ml in M and S group, respectively, and there was no significant difference. The incidence of adverse events was 8.4 %, although none were serious, and the patients recovered spontaneously after mirabegron was discontinued. Conclusion The present study suggests mirabegron is as effective as antimuscarinics for OAB. It improves OAB symptoms in patients with OAB for which antimuscarinic agents are insufficient. This study revealed that mirabegron improves not only OAB symptoms related to BPH, but also voiding symptoms in men. Low and mild incidences of side effects support the safe utility of mirabegron.
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