Mirabegron

Generic Name: Mirabegron

Brand Names: Myrbetriq

Mirabegron is a beta-3 adrenergic agonist for overactive bladder. Different mechanism than antimuscarinics with fewer anticholinergic side effects.

UrologyOveractive Bladder

Drug Class

Beta-3 Adrenergic Agonist

Pregnancy

Not formally categorized; animal studies showed adverse effects at high doses — use during pregnancy only if clearly needed

Available Forms

25 mg extended-release oral tablet, 50 mg extended-release oral tablet, 8 mg oral granules (pediatric, for neurogenic detrusor overactivity)

What It's Used For

Dosage Quick Reference

These are general dosage guidelines. Your doctor will determine the appropriate dose for your specific situation.

Condition	Starting Dose	Typical Maintenance Dose
Overactive bladder (OAB) in adults	25 mg once daily	25–50 mg once daily
OAB with severe hepatic impairment (Child-Pugh C)	Not recommended	Not recommended
OAB with severe renal impairment (eGFR 15–29)	25 mg once daily	25 mg once daily (do not exceed)
Neurogenic detrusor overactivity (pediatric ≥3 years)	Weight-based dosing with oral granules	Weight-based; consult prescribing information

Side Effects

Common Side Effects:

Hypertension
Urinary tract infection
Headache
Nasopharyngitis
Constipation
Diarrhea

Serious Side Effects:

Angioedema (face, lips, tongue, larynx)
Urinary retention
Severe hypertension
Atrial fibrillation (rare)

Drug Interactions

Major Drug & Food Interactions

Digoxin: Mirabegron inhibits P-glycoprotein and may increase digoxin levels; initiate digoxin at lowest dose and monitor serum concentrations.
CYP2D6 substrates with narrow therapeutic index (metoprolol, desipramine, thioridazine): Mirabegron is a moderate CYP2D6 inhibitor; co-administration increases levels of CYP2D6 substrates — monitor for dose-dependent toxicity.
Warfarin: Mirabegron may increase warfarin (S-warfarin) exposure via CYP2D6 inhibition; monitor INR.
Antimuscarinic OAB medications (solifenacin, oxybutynin): May be used in combination for refractory OAB, but increases risk of urinary retention; monitor for voiding difficulties.
Ketoconazole and other strong CYP3A4 inhibitors: Can increase mirabegron levels; no dose adjustment recommended, but use with caution in patients with renal/hepatic impairment.

Additional Information

Mirabegron is a selective beta-3 adrenergic receptor agonist used to treat overactive bladder (OAB) with symptoms of urge urinary incontinence, urgency, and urinary frequency. It represents an alternative mechanism to antimuscarinics for OAB treatment.

Mechanism of Action

Mirabegron activates beta-3 adrenergic receptors in the detrusor muscle of the bladder:

Beta-3 receptors are the predominant beta-adrenoceptor subtype in the bladder
Activation causes detrusor muscle relaxation during the storage phase
Relaxation increases bladder capacity and reduces urgency
Does not block muscarinic receptors, avoiding anticholinergic side effects

This mechanism is particularly advantageous for patients who cannot tolerate or have contraindications to antimuscarinics.

Available Formulations

Mirabegron is available as extended-release tablets (Myrbetriq):

25 mg tablets
50 mg tablets

Also available as:

Granules for oral suspension: 8 mg/mL (for pediatric use)

Tablets should be swallowed whole with water; do not crush, chew, or divide.

Medical Uses

FDA-Approved Indications:

Overactive bladder with symptoms of urge urinary incontinence, urgency, and urinary frequency in adults
Neurogenic detrusor overactivity (NDO) in pediatric patients 3 years and older

May be used alone or in combination with the antimuscarinic solifenacin (Vesicare) for enhanced efficacy.

Dosing Guidelines

Adults with OAB:

Starting dose: 25 mg once daily
May increase to 50 mg once daily based on efficacy and tolerability

Pediatric NDO (≥3 years):

Weight-based dosing using granules or tablets
11-22 kg: 24 mg once daily (may increase to 48 mg)
22-35 kg: 32 mg once daily (may increase to 64 mg)
≥35 kg: 40 mg once daily (may increase to 80 mg)

Important Safety Information

Contraindications:

Known hypersensitivity to mirabegron

Warnings and Precautions:

Hypertension: Can increase blood pressure; measure before starting and monitor periodically
Urinary retention: Use with caution in patients with bladder outlet obstruction or taking antimuscarinics
Angioedema: Discontinue immediately if occurs
CYP2D6 drug interactions: Mirabegron inhibits CYP2D6

Blood Pressure Monitoring: Check blood pressure before starting treatment and monitor periodically, especially in hypertensive patients.

Drug Interactions

CYP2D6 Substrates:

Metoprolol: Exposure increased; use lowest metoprolol dose and monitor
Desipramine: Exposure increased 3.4-fold; use lower desipramine doses
Thioridazine: Use not recommended (QT prolongation risk)

Other Interactions:

Digoxin: Exposure increased; use lowest digoxin dose and monitor levels
Warfarin: Monitor INR more frequently initially

Special Populations

Hepatic Impairment:
- Mild: No adjustment needed
- Moderate (Child-Pugh B): Do not exceed 25 mg daily
- Severe (Child-Pugh C): Not recommended
Renal Impairment:
- eGFR 15-29 mL/min: Do not exceed 25 mg daily
- eGFR <15 or ESRD: Not recommended
Pregnancy: Limited data; use only if benefit outweighs risk
Elderly: No dose adjustment required

Frequently Asked Questions

Mirabegron is a beta-3 adrenergic agonist that relaxes the bladder muscle by activating beta-3 receptors, whereas anticholinergics (solifenacin, oxybutynin, tolterodine) block muscarinic receptors. Because mirabegron does not block acetylcholine, it avoids the typical anticholinergic side effects of dry mouth, constipation, blurred vision, and cognitive impairment — making it particularly advantageous for older adults.

Yes. Mirabegron can cause a modest increase in blood pressure (typically 1–2 mmHg on average, but occasionally more significant). Blood pressure should be measured before starting and periodically during treatment. It is not recommended for patients with severe uncontrolled hypertension (systolic ≥180 mmHg or diastolic ≥110 mmHg).

Some patients notice improvement in urgency and frequency within the first 2 weeks. However, full therapeutic benefit may take 8 weeks. If the 25 mg dose provides insufficient relief after 8 weeks, your doctor may increase it to 50 mg daily.

Yes — combining mirabegron with solifenacin is an FDA-approved approach for patients whose OAB symptoms are not adequately controlled with either drug alone. The combination targets two different pathways and can be more effective. However, the combination increases the risk of urinary retention, so careful monitoring is needed.

Unlike anticholinergic bladder medications, mirabegron does not carry the same risk of worsening narrow-angle glaucoma because it does not have anticholinergic activity. This is another advantage for patients who have glaucoma and need OAB treatment.

Questions to Ask Your Doctor

Consider discussing these topics at your next appointment:

✓Would mirabegron be better for me than an anticholinergic, given my age and other conditions?
✓How will mirabegron affect my blood pressure, and how often should we monitor it?
✓Could combining mirabegron with my current bladder medication provide better symptom control?
✓Are there non-medication strategies I should try alongside mirabegron for overactive bladder?

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Medical Disclaimer: This information is for educational purposes only and should not be considered medical advice. Always consult with your healthcare provider before starting, stopping, or changing any medication. Your doctor can provide personalized recommendations based on your specific health condition and medical history.