Mirabegron

1. Introduction

Mirabegron is a beta-3 adrenergic receptor agonist used to treat overactive bladder (OAB). It works by relaxing the detrusor muscle of the bladder, increasing bladder capacity, and reducing symptoms like urinary urgency, frequency, and urge incontinence. It provides an alternative to antimuscarinics, especially in patients who cannot tolerate their side effects.

2. Indications

  • Overactive bladder (OAB) with symptoms of:
    • Urinary urgency
    • Increased urinary frequency
    • Urge incontinence

3. Dosage

Adults:

  • Starting dose: 25 mg once daily.
  • May increase to 50 mg once daily based on response and tolerability.

Children:

  • Not recommended; safety and efficacy have not been established for paediatric use.

Elderly:

  • No dose adjustment required unless there is severe renal or hepatic impairment.

4. Administration

  • Take orally once daily with or without food.
  • Swallow the tablet whole; do not chew, crush, or divide the tablet.

5. Forms Available

  • Extended-release tablets: 25 mg, 50 mg

6. Side Effects

6.1 Common Side Effects:

  • Increased blood pressure
  • Headache
  • Nasopharyngitis
  • Urinary tract infection (UTI)
  • Constipation

6.2 Less Common Side Effects:

  • Dizziness
  • Abdominal pain
  • Fatigue

6.3 Rare but Serious Side Effects:

  • Angioedema (swelling of the face, lips, or tongue)
  • Severe hypertension
  • Tachycardia or arrhythmias

7. Warnings

  • Hypertension: Mirabegron can increase blood pressure; avoid in patients with severe uncontrolled hypertension.
  • Urinary Retention: Use cautiously in patients with bladder outlet obstruction or those taking antimuscarinic medications, as it may increase the risk of urinary retention.
  • Angioedema: Rare cases of angioedema have been reported; discontinue immediately if this occurs.

8. Precautions

  • Monitor blood pressure regularly, especially in patients with pre-existing hypertension.
  • Use cautiously in patients with severe renal or hepatic impairment.
  • Avoid use in patients with a history of hypersensitivity to Mirabegron or its components.

9. Interactions

  • CYP2D6 substrates (e.g., metoprolol, desipramine): Mirabegron inhibits CYP2D6, potentially increasing plasma levels of these drugs.
  • Digoxin: Increases digoxin levels; monitor digoxin serum levels and adjust dose accordingly.
  • Antimuscarinics (e.g., solifenacin): Increased risk of urinary retention when used concurrently.

10. Monitoring Parameters

  • Blood pressure (baseline and periodically during treatment).
  • Symptoms of urinary retention, especially in patients with risk factors.
  • Signs of hypersensitivity or angioedema.

11. Use in Children

  • Safety and efficacy have not been established in paediatric patients.

12. Use in Pregnancy

  • Not recommended unless clearly needed; no adequate data on the use of Mirabegron during pregnancy.

13. Use in Elderly

  • No specific dose adjustment required, but monitor for side effects, particularly increased blood pressure.

14. Use in Kidney Disease

  • Mild to moderate renal impairment: No dose adjustment needed.
  • Severe renal impairment (eGFR 15–29 mL/min/1.73m²): Limit dose to 25 mg once daily.
  • End-stage renal disease (eGFR <15 mL/min/1.73m²): Not recommended.

15. Use in Liver Disease

  • Mild hepatic impairment (Child-Pugh A): No dose adjustment needed.
  • Moderate hepatic impairment (Child-Pugh B): Limit dose to 25 mg once daily.
  • Severe hepatic impairment (Child-Pugh C): Not recommended.

16. Patient Counselling Points

  • Take the tablet once daily as prescribed; swallow whole with water.
  • Inform your doctor if you experience difficulty urinating, severe dizziness, or swelling of the face or lips.
  • Regularly monitor your blood pressure if you have hypertension or cardiovascular conditions.
  • Do not stop taking Mirabegron without consulting your doctor.
  • Store the medication in a cool, dry place, away from moisture and sunlight.

17. Table of Brand Names, Manufacturer, and Prices in USD

Brand NameManufacturerStrength/Dosage FormPrice (USD)
MyrbetriqAstellas Pharma25 mg Extended-Release Tablet$330 (30 tablets)
BetmigaAstellas Pharma50 mg Extended-Release Tablet$350 (30 tablets)

18. 15 FAQs (Frequently Asked Questions)

1. What is Mirabegron?
Mirabegron is a beta-3 adrenergic agonist used to treat overactive bladder (OAB).

2. How does Mirabegron work?
It relaxes the detrusor muscle in the bladder, increasing bladder capacity and reducing symptoms of OAB.

3. What is the usual dose of Mirabegron?
The starting dose is 25 mg once daily, which can be increased to 50 mg based on response.

4. How long does it take for Mirabegron to work?
Improvement in symptoms may be observed within 2–8 weeks of starting treatment.

5. Can Mirabegron be used during pregnancy?
It is not recommended unless clearly necessary, as safety data in pregnancy are limited.

6. Is Mirabegron safe for children?
No, it is not approved for use in children.

7. Can Mirabegron increase blood pressure?
Yes, it may cause or worsen hypertension. Monitor blood pressure regularly during treatment.

8. Can Mirabegron cause urinary retention?
Yes, it may increase the risk of urinary retention, especially in patients with bladder outlet obstruction.

9. Can I take Mirabegron with other medications?
It may interact with drugs metabolised by CYP2D6 (e.g., metoprolol) or digoxin. Consult your doctor before combining medications.

10. How should Mirabegron be taken?
Take it once daily with or without food. Swallow the tablet whole without crushing or chewing.

11. Is Mirabegron better than antimuscarinics?
It is an alternative to antimuscarinics, especially for patients who experience dry mouth or other side effects from those medications.

12. Can Mirabegron cause weight gain?
Weight gain is not a common side effect of Mirabegron.

13. What happens if I miss a dose of Mirabegron?
Take the missed dose as soon as you remember, but skip it if it is close to your next scheduled dose. Do not double the dose.

14. How long can I take Mirabegron?
It is typically used as a long-term treatment for OAB, but your doctor will determine the duration based on your response and tolerance.

15. Do I need a prescription for Mirabegron?
Yes, Mirabegron is a prescription-only medication.