To evaluate the additional effects of mirabegron to alpha-1 adrenergic antagonist on lower urinary tract symptoms of patients who underwent ¹²⁵I-brachytherapy for prostate cancer.

Patients who underwent ¹²⁵I-brachytherapy for prostate cancer (cT1-cT3aN0M0) in a single institute between September 2016 and October 2018 were enrolled in the randomized, non-placebo, open-labeled, paralleled study. Patients were randomly distributed (1:1) to combination group (tamsulosin (0.2 mg/day) plus mirabegron (50 mg/day)) or tamsulosin-alone group after ¹²⁵I -brachytherapy by envelope method. The primary endpoint was the change from baseline in mean voided volume per micturition 3 months after ¹²⁵I brachytherapy. The secondary endpoints included the changes from baseline of International Prostate Symptom Score, Overactive Bladder Symptom Score, and Expanded Prostate Cancer Index Composite scores and 24 hours urinary frequency after 3 months after ¹²⁵I brachytherapy.

The mean changes in volume voided per micturition in the combination (n = 108) and tamsulosin-alone (n = 110) groups were −62.5 (standard deviation, ±53.8) and −68.0 (standard deviation, ±52.7), respectively (P = .17). The change in Overactive Bladder Symptom Score in combination group (P = .02) was more moderate than in tamsulosin-alone group; and 24 hour urinary frequency in combination group was lower (P = .03) than in tamsulosin-alone group. Retention rates within 3 months after ¹²⁵I-brachytherapy in the mirabegron and tamsulosin-alone groups were 7.3% (9/122) and 6.0% (7/118), respectively (P = .80).

Tamsulosin and mirabegron combination therapy after ¹²⁵I-brachytherapy did not improve voided volume per micturition compared to tamsulosin-only treatment. However, it could improve frequent urination and overactive bladder symptoms.