Mirabegron (Myrbetriq) for Incontinence
Mirabegron is an effective second-line pharmacologic treatment for overactive bladder with urge urinary incontinence, offering comparable efficacy to antimuscarinics but with significantly lower rates of dry mouth and other anticholinergic side effects. 1, 2
FDA-Approved Indication and Dosing
Mirabegron is FDA-approved for treating overactive bladder (OAB) in adults with symptoms of urge urinary incontinence, urgency, and urinary frequency. 2
Starting dose: 25 mg orally once daily 2
Dose escalation: After 4-8 weeks, may increase to maximum dose of 50 mg once daily if needed 2
Administration: Swallow tablets whole with water; do not chew, divide, or crush. Can be taken with or without food in adults. 2
Clinical Efficacy
Mirabegron 50 mg once daily demonstrates significant improvements in key incontinence outcomes:
- Reduces incontinence episodes per 24 hours with benefits evident as early as week 4 and maintained throughout treatment 3, 4
- Decreases micturition frequency and urgency episodes 3, 4
- Increases volume voided per micturition 3
- Improves health-related quality of life and treatment satisfaction 3, 4
The drug shows comparable efficacy to tolterodine extended-release 4 mg based on 12-month trial data. 3
Combination Therapy for Refractory Cases
For patients inadequately responding to mirabegron monotherapy, combination with an antimuscarinic agent (specifically solifenacin 5 mg) is supported by Grade B evidence. 1
The strongest evidence comes from the SYNERGY I/II and BESIDE trials:
- Mirabegron 50 mg + solifenacin 5 mg demonstrates statistically superior efficacy compared to either monotherapy for reducing incontinence episodes, urgency episodes, and nocturia 1, 5
- Effect sizes are additive: Combination therapy (0.65-0.95) exceeds monotherapy (0.36-0.56) 6
- Safety profile: Combination therapy shows slightly increased rates of dry mouth, constipation, and dyspepsia compared to monotherapy, with more frequent urinary retention events 1
Safety Profile and Monitoring Requirements
Key advantage over antimuscarinics: Dry mouth occurs at rates similar to placebo (2.8% vs 8.6% with tolterodine ER over 12 months) 3, 4
Critical monitoring requirement: Periodically monitor blood pressure, especially in hypertensive patients and during initial treatment, as mirabegron can cause dose-dependent blood pressure increases 6, 2
Common adverse events (>2%): 2, 3
- Hypertension
- Nasopharyngitis
- Urinary tract infection
- Headache
Serious but rare adverse effects: 2
- Angioedema of face, lips, tongue, and/or larynx
- Cardiac arrhythmias (especially tachycardia)
- Kidney stones
- Serious skin reactions
Special Populations and Contraindications
Renal impairment dosing: 2
- eGFR 30-89 mL/min/1.73 m²: Start 25 mg, max 50 mg daily
- eGFR 15-29 mL/min/1.73 m²: Start 25 mg, max 25 mg daily
- eGFR <15 mL/min/1.73 m² or dialysis: Not recommended
Hepatic impairment dosing: 2
- Child-Pugh Class A (mild): Start 25 mg, max 50 mg daily
- Child-Pugh Class B (moderate): Start 25 mg, max 25 mg daily
- Child-Pugh Class C (severe): Not recommended
Older patients (≥65 years): Mirabegron 25 mg is particularly effective and safe in this population with multiple comorbidities 7, 6
Contraindications: 2
- Hypersensitivity to mirabegron or inactive ingredients
- Severe uncontrolled hypertension (not recommended)
Critical Clinical Caveats
Urinary retention risk: Administer with caution in patients with bladder outlet obstruction or those taking muscarinic antagonists, as mirabegron increases urinary retention risk 2
For men with lower urinary tract symptoms: Regular re-evaluation of symptoms and post-void residual volume is necessary 7, 6
Drug interactions: Mirabegron is a CYP2D6 inhibitor; when used with drugs metabolized by CYP2D6 (especially narrow therapeutic index drugs), appropriate monitoring and dose adjustment may be necessary 2
Pregnancy: Should not be used by women who are or may be pregnant due to lack of clinical data 8