In a patient ≥65 years old with new‑onset urinary incontinence, what is the recommended starting dose of mirabegron, how should it be titrated, and what monitoring is required considering renal or hepatic impairment and blood pressure status?

Mirabegron Dosing in Elderly Patients with New-Onset Urinary Incontinence

Start with mirabegron 25 mg once daily in patients ≥65 years with new-onset urinary incontinence, as this dose is particularly effective and safe in older patients with multiple comorbidities. 1, 2

Starting Dose and Rationale

• Begin with 25 mg once daily in elderly patients (≥65 years), as this dose demonstrates both safety and therapeutic efficacy in older populations with overactive bladder and multiple comorbidities 1, 3
• The 25 mg dose is specifically recommended for older patients rather than the standard 50 mg dose used in younger populations 1, 2
• Clinical trials have confirmed efficacy of 25 mg in patients ≥65 and ≥75 years, with significant reductions in incontinence episodes and micturition frequency 4

Dose Titration Strategy

• After 4-8 weeks, consider increasing to 50 mg once daily if the patient has inadequate symptom control and tolerates the initial dose well 1, 5
• The dose escalation should be based on both patient response and investigator assessment of tolerability 5
• Flexible dosing (starting at 25 mg with option to increase to 50 mg) has been validated in elderly patients in the PILLAR study 5

Monitoring Requirements

Blood Pressure Monitoring

• Monitor blood pressure periodically, especially during initial treatment and in patients with pre-existing hypertension 1, 2
• Mirabegron can cause dose-dependent blood pressure increases, though the clinical significance is generally modest 2, 6
• Approximately 20% of patients may experience systolic BP increases ≥10 mmHg, with higher rates in older patients (23.4% in ≥65 years vs 7.4% in <65 years) 6
• Mirabegron is contraindicated in severe uncontrolled hypertension 7, 2

Voiding Function Assessment

• Regularly re-evaluate symptoms and post-void residual (PVR) volume, particularly in male patients with lower urinary tract symptoms 7, 1
• Mirabegron does not significantly affect voiding urodynamic parameters, and overall changes in PVR are small 7
• Advise patients to discontinue medication if worsening voiding symptoms or urinary stream occurs after initiation 7, 1

Renal Function Considerations

• For patients with eGFR 30-89 mL/min/1.73 m²: start with 25 mg, maximum 50 mg daily 8
• No specific dose adjustment is mentioned for mild renal impairment, but the 25 mg starting dose in elderly patients provides an inherent safety margin 8

Hepatic Function Considerations

• For patients with Child-Pugh Class A (mild hepatic impairment): start with 25 mg, maximum 50 mg daily 8
• More severe hepatic impairment requires additional caution 8

Common Adverse Events to Monitor

• Most frequent adverse events: hypertension, urinary tract infections, headache, and nasopharyngitis 7, 2, 9
• Anticholinergic effects are minimal: dry mouth incidence is similar to placebo and 3-6 fold lower than tolterodine, making mirabegron particularly suitable for elderly patients who are vulnerable to anticholinergic burden 2, 4, 9
• Serious but rare adverse effects include angioedema, cardiac arrhythmias, kidney stones, and serious skin reactions 8

Key Clinical Advantages in Elderly Patients

• Mirabegron is well tolerated in elderly patients with multiple comorbidities 7, 4, 3
• Does not cause significant anticholinergic effects such as dry mouth, constipation, and cognitive impairment—critical considerations in older adults 2
• Efficacy is maintained in patients ≥75 years, with statistically significant improvements in incontinence episodes and micturition frequency 4, 5

Combination Therapy Option

• If inadequate response to 25-50 mg mirabegron monotherapy after adequate trial: consider combination with solifenacin 5 mg once daily 1, 8
• Combination therapy (mirabegron 25 mg + solifenacin 5 mg or mirabegron 50 mg + solifenacin 5 mg) provides superior efficacy compared to monotherapy without significant safety concerns 1, 8, 2
• Do not use combination therapy as first-line treatment; reserve for patients refractory to monotherapy 8

Critical Pitfalls to Avoid

• Do not start with 50 mg in elderly patients—the 25 mg dose is specifically validated and recommended for this population 1, 2, 3
• Do not neglect blood pressure monitoring, particularly in the first few months of treatment 1, 2, 6
• Do not use in patients with severe uncontrolled hypertension 7, 2
• Do not overlook the need for regular symptom and PVR reassessment, especially in men 7, 1