What is Myrbetriq (mirabegron)?

Mirabegron (Myrbetriq): A Beta-3 Adrenergic Receptor Agonist for Overactive Bladder

Mirabegron (Myrbetriq) is a beta-3 adrenergic receptor agonist that relaxes the detrusor smooth muscle during bladder filling, increasing bladder capacity and effectively treating overactive bladder symptoms with a lower risk of dry mouth compared to antimuscarinic medications. 1, 2

Mechanism of Action

Mirabegron works differently from traditional overactive bladder medications:

• Acts as an agonist of the beta-3 adrenergic receptors in the bladder 2
• Relaxes the detrusor smooth muscle during the storage phase of the urinary bladder fill-void cycle 2
• Increases bladder capacity by activating beta-3 adrenergic receptors 2

Clinical Efficacy

Mirabegron demonstrates significant improvements in key overactive bladder symptoms:

• Reduces frequency of urination (micturition frequency) 1, 3
• Decreases urgency incontinence episodes 3
• Improves urgency episodes 4, 3
• Increases mean volume voided per micturition 4, 3
• Shows efficacy as early as 4 weeks after starting treatment 4
• Benefits both treatment-naïve patients and those who previously discontinued antimuscarinic therapy 4
• Effective in patients ≥65 years of age 4, 5

Dosing Information

• Available in 25 mg and 50 mg extended-release tablets 2
• Standard adult dosing is 25-50 mg once daily 2
• Dose adjustments required for:
  • Severe renal impairment (eGFR 15-29 mL/min/1.73m²): maximum 25 mg daily 2
  • Moderate hepatic impairment (Child-Pugh Class B): maximum 25 mg daily 2
  • Not recommended for end-stage renal disease or severe hepatic impairment 2

Safety Profile

Mirabegron offers a favorable safety profile compared to antimuscarinic agents:

• Most common adverse events include hypertension, nasopharyngitis, urinary tract infection, and headache 2, 4, 5
• Notably, the incidence of dry mouth is similar to placebo (0.5-2.1%) and 3-5 times lower than with antimuscarinic medications 4, 3, 6
• Well-tolerated in elderly patients and those with multiple comorbidities 1, 5
• Does not significantly affect voiding urodynamic parameters or post-void residual volume 1, 2
• Cardiovascular effects include dose-dependent increases in heart rate and blood pressure 2

Important Precautions

• Contraindicated in patients with severe uncontrolled hypertension 1
• Should be used with caution in patients with clinically significant bladder outlet obstruction 2
• Regular monitoring of blood pressure is recommended, especially at treatment initiation 2
• At therapeutic doses (50 mg), QTc prolongation risk is low 2

Advantages Over Antimuscarinic Medications

• Significantly lower incidence of dry mouth (2.8% vs 8.6% with tolterodine ER) 6
• Lower rates of constipation and CNS effects 7
• May be particularly beneficial for patients who cannot tolerate antimuscarinic side effects 4, 7
• Maintains efficacy and safety over 12 months of treatment 6, 7

Clinical Considerations

• Can be used as first-line therapy for overactive bladder or after failure of antimuscarinic agents 4, 7
• Effective in both men and women with overactive bladder 5
• May be combined with antimuscarinic agents for enhanced efficacy in refractory cases 1
• Provides clinically meaningful improvements in health-related quality of life and treatment satisfaction 4

Mirabegron represents an important alternative to antimuscarinic medications for overactive bladder treatment, particularly for patients concerned about dry mouth and other anticholinergic side effects.