Mirabegron Treatment for Overactive Bladder
Recommended Dosing Strategy
Start mirabegron at 25 mg orally once daily, then increase to 50 mg once daily after 4-8 weeks if symptom control remains inadequate. 1
Initial Dosing
- Begin with 25 mg once daily taken with water, swallowed whole (do not crush, chew, or divide) 1
- Can be taken with or without food in adults 1
- This starting dose is FDA-approved and particularly appropriate for elderly patients (≥65 years) with multiple comorbidities 2, 3
Dose Escalation
- After 4-8 weeks, increase to 50 mg once daily if symptoms persist 1, 3
- The 50 mg dose demonstrates superior efficacy with effect sizes of 0.36-0.56 for key outcomes 4
- Both doses showed statistically significant reductions in incontinence episodes (-1.47 for 50 mg vs -1.13 for placebo) and micturitions per 24 hours (-1.66 for 50 mg vs -1.05 for placebo) 5
Monitoring Requirements
Blood Pressure Surveillance
- Monitor blood pressure periodically, especially during initial treatment, as mirabegron causes dose-dependent blood pressure increases 3, 1
- Mirabegron is contraindicated in severe uncontrolled hypertension 3, 1
- The cardiovascular safety profile has been validated in large integrated databases 6
Urinary Function Assessment
- In men with lower urinary tract symptoms, regularly re-evaluate post-void residual volume 3
- Advise patients to discontinue if worsening voiding symptoms or urinary stream occurs after initiation 2
- Administer with caution in patients with bladder outlet obstruction due to urinary retention risk 1
Combination Therapy for Inadequate Response
If monotherapy provides insufficient symptom control after 6 months, add solifenacin 5 mg once daily to mirabegron. 2, 3
Evidence-Based Combination Regimens
- Two validated options exist: mirabegron 25 mg + solifenacin 5 mg OR mirabegron 50 mg + solifenacin 5 mg once daily 2, 4
- Combination therapy demonstrates superior efficacy with effect sizes of 0.65-0.95, substantially exceeding monotherapy 4
- The SYNERGY trials showed combination therapy was statistically superior for decreasing incontinence episodes and micturitions over 12 months 6, 3
Combination Therapy Considerations
- Slightly increased risk of adverse events including dry mouth, constipation, and urinary retention compared to monotherapy 3
- The safety profile remains acceptable despite increased adverse event rates 6
Safety Profile and Tolerability
Common Adverse Events
- Most frequently reported adverse reactions (>2% and >placebo): hypertension, nasopharyngitis, urinary tract infection, and headache 1
- Dry mouth occurs in only 0.5-2.1% of mirabegron patients compared to 8.6% with tolterodine 7
- Overall adverse event rate with 50 mg dose is similar to placebo over 12 weeks 7
Special Populations
- In elderly patients ≥80 years with multiple comorbidities, the 25 mg dose produces statistically significant improvements with an acceptable adverse event rate of 24.62% 3, 4
- Cardiovascular safety has been established in patients with overactive bladder syndrome 6
Key Clinical Pitfalls to Avoid
- Do not use in severe uncontrolled hypertension without first achieving blood pressure control 3, 1
- Do not crush or divide tablets, as this destroys the extended-release formulation 1
- Do not combine with muscarinic antagonists initially—reserve combination therapy for inadequate monotherapy response after 6 months 2, 3
- Monitor for angioedema of face, lips, tongue, or larynx, which has been reported with mirabegron 1
- Exercise caution with CYP2D6 substrates, especially narrow therapeutic index drugs, as mirabegron is a CYP2D6 inhibitor requiring dose adjustment monitoring 1