What is the recommended dose and frequency of Mirabegron (Myrbetric) for treating overactive bladder?

Mirabegron Dosing for Overactive Bladder

Start mirabegron at 25 mg orally once daily, and if needed after 4-8 weeks, increase to the maximum dose of 50 mg orally once daily. 1

Standard Dosing Regimen

• Initial dose: 25 mg once daily 1
• Titration timing: Increase after 4-8 weeks if inadequate symptom control 1
• Maximum dose: 50 mg once daily 1
• Administration: Take as extended-release tablets once daily 1

The FDA-approved dosing is straightforward and supported by extensive clinical trial data showing dose-dependent efficacy improvements. 2

Efficacy by Dose

• 25 mg dose: Produces statistically significant reductions in micturition frequency (1.9 episodes/24h reduction vs 1.4 with placebo) 2
• 50 mg dose: Demonstrates superior efficacy with 2.1 episodes/24h reduction and consistent improvements in urgency incontinence, urgency episodes, and voided volume 2
• Onset of action: Significant improvements observed as early as week 4 and maintained throughout treatment 3

Both doses are effective, but the 50 mg dose shows more robust and consistent improvements across all overactive bladder symptoms. 4, 3

Dose Modifications for Special Populations

Renal Impairment

• eGFR 30-89 mL/min/1.73m²: Start 25 mg, may increase to 50 mg 1
• eGFR 15-29 mL/min/1.73m²: Maximum dose 25 mg once daily 1
• eGFR <15 mL/min/1.73m² or dialysis: Not recommended 1

Hepatic Impairment

• Child-Pugh Class A (mild): Start 25 mg, may increase to 50 mg 1
• Child-Pugh Class B (moderate): Maximum dose 25 mg once daily 1
• Child-Pugh Class C (severe): Not recommended 1

Elderly Patients

• Age ≥65 years: Standard dosing applies, though 25 mg is particularly appropriate for those ≥80 years with multiple comorbidities 5
• The 25 mg dose produces statistically significant improvements in voiding symptoms and quality of life in elderly patients with an acceptable adverse event rate of 24.62% 5

Monitoring Requirements

• Blood pressure: Monitor periodically, especially during initial treatment, as mirabegron can cause dose-dependent blood pressure increases 5
• Contraindication: Severe uncontrolled hypertension 5
• Post-void residual volume: Regular re-evaluation advised, particularly in men with lower urinary tract symptoms 6
• Discontinuation criteria: Stop if worsening voiding symptoms or urinary stream occurs after initiation 6

Combination Therapy for Inadequate Response

If monotherapy provides inadequate response after 6 months:

• Add solifenacin 5 mg once daily to mirabegron (either 25 mg or 50 mg) 6, 5
• Two validated regimens: Mirabegron 25 mg + solifenacin 5 mg OR mirabegron 50 mg + solifenacin 5 mg 6
• Superior efficacy: Combination therapy shows effect sizes (0.65-0.95) exceeding monotherapy (0.36-0.56) 5
• Trade-off: Slightly increased adverse events including dry mouth, constipation, and urinary retention compared to monotherapy 7

The SYNERGY trials demonstrated that combination therapy was statistically superior to either monotherapy for decreasing incontinence episodes and micturitions over 12 months. 7

Common Pitfalls to Avoid

• Premature dose escalation: Wait the full 4-8 weeks before increasing from 25 mg to 50 mg to allow adequate time for therapeutic response 1
• Ignoring renal/hepatic function: Always check kidney and liver function before prescribing, as dose adjustments are mandatory in moderate impairment 1
• Overlooking cardiovascular risk: While pulse rate increases were noted at higher doses (100-200 mg) in trials, this was not associated with increased cardiovascular adverse events at approved doses 2
• Not counseling about dry mouth expectations: Unlike antimuscarinics, mirabegron has a dry mouth incidence similar to placebo and 3-5 fold less than tolterodine, which improves adherence 3