What is the recommended treatment and dosage for overactive bladder using Myrbetriq (mirabegron)?

Mirabegron (Myrbetriq) Treatment for Overactive Bladder

The recommended treatment for overactive bladder using Myrbetriq (mirabegron) is to start with 25 mg orally once daily, with the option to increase to 50 mg once daily after 4-8 weeks if needed and tolerated. 1, 2

Dosing Guidelines

• Starting dose: 25 mg orally once daily
• Maximum dose: 50 mg orally once daily (if needed after 4-8 weeks)
• Administration: Take with or without food

Dosage Adjustments for Special Populations

Renal Impairment

• eGFR 30-89 mL/min/1.73 m²: 25 mg starting dose, may increase to 50 mg
• eGFR 15-29 mL/min/1.73 m²: 25 mg maximum dose
• eGFR <15 mL/min/1.73 m²: Not recommended 2

Hepatic Impairment

• Child-Pugh Class A (mild): 25 mg starting dose, may increase to 50 mg
• Child-Pugh Class B (moderate): 25 mg maximum dose
• Child-Pugh Class C (severe): Not recommended 2

Efficacy

Mirabegron has demonstrated significant efficacy in treating OAB symptoms:

• Reduces incontinence episodes per 24 hours
• Decreases micturition frequency per 24 hours
• Reduces urgency episodes
• Increases volume voided per micturition 3, 4

Improvements in these parameters are typically observed as early as 4 weeks after treatment initiation and are maintained throughout treatment 5.

Advantages Over Antimuscarinic Medications

Mirabegron offers several advantages over antimuscarinic medications:

• Lower incidence of dry mouth: 0.5-2.1% with mirabegron vs. 8.6% with tolterodine ER 4 mg 3, 5
• Better tolerability profile: Particularly regarding cognitive effects and dry mouth 1
• Similar efficacy to antimuscarinic medications: But with fewer anticholinergic side effects 6

Common Side Effects

• Hypertension
• Nasopharyngitis
• Urinary tract infection 5, 6

Monitoring Recommendations

• Blood pressure: Regular monitoring, especially in patients with pre-existing hypertension
• Urinary retention: Monitor for symptoms, especially in the first few weeks of treatment
• Post-void residual volume: Consider checking in patients at risk for urinary retention 1

Treatment Algorithm for OAB

1. First-line: Behavioral therapies (pelvic floor muscle training, bladder training, fluid management)
2. Second-line options:
   • Antimuscarinic medications (e.g., solifenacin 5 mg daily)
   • Mirabegron 25 mg daily (especially for patients who cannot tolerate antimuscarinic side effects)
3. Inadequate response to monotherapy:
   • Increase mirabegron to 50 mg daily after 4-8 weeks if needed
   • Consider combination therapy (mirabegron plus solifenacin 5 mg) for patients who fail monotherapy 1
4. Third-line options (for patients who fail second-line therapies):
   • OnabotulinumtoxinA injections
   • Peripheral tibial nerve stimulation
   • Sacral neuromodulation 1

Important Considerations

• Complete symptom relief is unlikely in patients with severe baseline symptoms
• Patients who are refractory to behavioral and medical therapy should be evaluated by a specialist
• Regular follow-up at 4-8 weeks after treatment initiation is recommended to assess efficacy and tolerability 1

Pitfalls to Avoid

• Avoid use in severe uncontrolled hypertension: Monitor blood pressure regularly
• Avoid use in severe hepatic impairment: Adjust dose in moderate impairment
• Avoid use in end-stage renal disease: Adjust dose in moderate to severe renal impairment
• Don't expect immediate results: Efficacy typically improves over 4-8 weeks of treatment 1, 2