What is the recommended dose of Mirabegron (beta-3 adrenergic agonist) for overactive bladder?

Mirabegron Dosing for Overactive Bladder

The recommended starting dose of mirabegron for overactive bladder in adults is 25 mg orally once daily, with the option to increase to 50 mg once daily after 4 to 8 weeks if needed. 1

Standard Dosing Algorithm

Initial Dosing

• Start all adult patients with OAB on mirabegron 25 mg once daily 1
• Assess response at 4 to 8 weeks 1
• If inadequate symptom control, escalate to the maximum dose of 50 mg once daily 1

Dose Modifications for Renal Impairment

The dosing must be adjusted based on estimated glomerular filtration rate (eGFR): 1

• eGFR 30-89 mL/min/1.73 m²: Start 25 mg, may increase to maximum 50 mg 1
• eGFR 15-29 mL/min/1.73 m²: Start 25 mg, maximum dose remains 25 mg (do not escalate) 1
• eGFR <15 mL/min/1.73 m² or dialysis: Mirabegron is not recommended 1

Dose Modifications for Hepatic Impairment

Adjust dosing based on Child-Pugh classification: 1

• Child-Pugh Class A (mild): Start 25 mg, may increase to maximum 50 mg 1
• Child-Pugh Class B (moderate): Start 25 mg, maximum dose remains 25 mg (do not escalate) 1
• Child-Pugh Class C (severe): Mirabegron is not recommended 1

Evidence Supporting Dosing Strategy

Efficacy at Both Doses

Both 25 mg and 50 mg doses demonstrate significant efficacy compared to placebo: 2, 3

• Mirabegron 50 mg consistently shows superior efficacy across all endpoints, with improvements evident as early as week 4 and maintained throughout 12 months of treatment 3
• Mirabegron 25 mg also demonstrates significant reductions in incontinence episodes and micturition frequency, though effect sizes are generally smaller than the 50 mg dose 2

Special Population: Older Adults

The 25 mg dose is particularly appropriate for elderly patients (≥80 years) with multiple comorbidities: 4

• A prospective study showed that mirabegron 25 mg once daily produced statistically significant improvements in voiding symptoms, quality of life, and bladder condition in patients aged ≥80 years after 3 months 4
• The adverse event rate was acceptably low (24.62%) in older patients, lower than in younger patients (41.94%) 4
• This makes 25 mg a safe and effective starting dose for elderly patients with comorbidities 5, 6

Combination Therapy for Refractory Cases

If monotherapy with mirabegron at maximum dose (50 mg) provides inadequate response after 6 months: 7, 5

• Consider adding solifenacin 5 mg once daily to create combination therapy 7
• The strongest evidence supports two validated regimens: mirabegron 25 mg + solifenacin 5 mg OR mirabegron 50 mg + solifenacin 5 mg 7, 5
• Combination therapy demonstrates superior efficacy compared to either monotherapy, with effect sizes (0.65-0.95) exceeding monotherapy (0.36-0.56) 7, 6
• The SYNERGY I/II and BESIDE trials provide Grade B evidence for this approach 7

Critical Monitoring Requirements

Blood Pressure Monitoring

• Monitor blood pressure periodically, especially during initial treatment 6
• This is particularly important in patients with pre-existing hypertension, as mirabegron can cause dose-dependent blood pressure increases 6
• Mirabegron is contraindicated in severe uncontrolled hypertension 6

For Male Patients with LUTS

• Regularly re-evaluate symptoms and measure post-void residual volume 6
• Advise patients to discontinue if worsening voiding symptoms or urinary stream occurs after initiation 5

Common Pitfalls to Avoid

• Do not escalate beyond 25 mg in patients with moderate renal impairment (eGFR 15-29) or moderate hepatic impairment (Child-Pugh B) 1
• Do not substitute mirabegron extended-release tablets with mirabegron granules on a milligram-per-milligram basis - these are different products 1
• Do not overlook the lower anticholinergic burden - dry mouth incidence with mirabegron 50 mg (2.8% at 12 months) is significantly lower than tolterodine ER 4 mg (8.6%), making it preferable for patients who discontinued antimuscarinics due to dry mouth 2, 8