Overactive bladder (OAB) is a prevalent condition that significantly affects patients' quality of life. This prospective clinical study aimed to evaluate the effectiveness of an initial one-month Mirabegron treatment, followed by randomization into three treatment groups for patients with insufficient response, comparing their outcomes.

A total of 61 patients diagnosed with OAB initially received Mirabegron for one month. Patients who showed inadequate response were regarded as having persistent OAB (definition: residual OAB symptoms (OABSS total score ≥3 points, OABSS question 3 score ≥2 points)). They were then randomly assigned into three groups: continued Mirabegron monotherapy (n=21), Solifenacin monotherapy (n=17), and combination therapy with both agents (n=24). Baseline characteristics, including age, BMI, urodynamic study (UDS) parameters, post-void residual urine volume (PVR), and various symptom scores, were recorded. Outcome measures were assessed at baseline, 4 weeks, and 12 weeks using the International Prostate Symptom Score (IPSS), Overactive Bladder Symptom Score (OABSS), and urinary diary evaluations. Generalized estimating equations (GEE) models were used to analyze treatment effects.

After the initial Mirabegron treatment, patients with persistent OAB were randomized into the three treatment groups. At 4 weeks post-randomization, nocturia frequency significantly decreased in the combination therapy group (p=0.0135). At 12 weeks, the combination therapy group demonstrated superior improvements in OAB-related symptoms compared to monotherapies. The adjusted GEE model indicated that combination therapy was associated with a greater reduction in nocturia episodes (-0.647, p=0.0104) and improved mean voided volume compared to Mirabegron alone. When comparing Solifenacin to combination therapy, PVR was significantly higher in the Solifenacin group (p=0.0149), while mean voided volume improvement favored the combination group (p=0.0161). No significant differences were observed in IPSS and OABSS total scores among groups.

For OAB patients who did not respond adequately to initial Mirabegron monotherapy, combination therapy with Mirabegron and Solifenacin provided superior symptom improvement compared to continued monotherapy, particularly in reducing nocturia and enhancing mean voided volume. Further studies with larger sample sizes are warranted to confirm these findings and evaluate long-term safety profiles.