Mirabegron 💊

Always check the BNF link here for latest guidance.

💊 Mirabegron: big picture - Mirabegron is a β3-adrenoceptor agonist used for symptoms of overactive bladder. It is useful when antimuscarinic drugs are ineffective, not tolerated, or unsuitable, but the key safety issue is blood pressure.

• ✅ Consider if antimuscarinics are not effective, not tolerated, or unsuitable.
• ✅ Particularly useful where antimuscarinic adverse effects are problematic, such as dry mouth, constipation, cognitive burden, or frailty concerns.
• ⚠️ Check blood pressure before starting and monitor during treatment.

⚙️ Mode of Action

• Mirabegron is a β3-adrenoceptor agonist.
• It relaxes the detrusor muscle during the bladder storage phase.
• This increases bladder capacity and reduces urinary urgency, frequency, and urge incontinence.

💊 Indications

• Symptomatic treatment of overactive bladder.
• Symptoms include:
  • Urinary urgency
  • Increased urinary frequency
  • Urge urinary incontinence

💊 Dose

• Adult dose: Mirabegron modified-release 50 mg once daily.
• Administration: swallow whole with water; do not chew, crush, or divide.
• Can be taken with or without food.
• Take at the same time each day where possible.

🧪 Dose adjustment: renal / hepatic impairment

• Renal impairment: dose reduction may be needed in severe renal impairment.
• Severe renal impairment: consider 25 mg once daily, depending on eGFR and interacting medicines.
• End-stage renal disease / dialysis: avoid unless specialist advice supports use.
• Hepatic impairment: use with caution; dose reduction may be needed in mild/moderate hepatic impairment.
• Severe hepatic impairment: avoid.
• Always check the BNF for the exact renal/hepatic dose because recommendations depend on severity and interacting medicines.

🔄 Interactions

• Strong CYP3A inhibitors may increase mirabegron exposure.
• Examples include ketoconazole, itraconazole, ritonavir, and clarithromycin.
• Dose adjustment with strong CYP3A inhibitors depends on renal and hepatic function.
• Mirabegron is a moderate CYP2D6 inhibitor.
• Use caution with narrow-therapeutic-index CYP2D6 substrates, such as flecainide, propafenone, some antidepressants, and some antipsychotics.
• Mirabegron may increase digoxin exposure; consider starting digoxin at the lowest appropriate dose and monitoring levels if clinically indicated.
• ⚡ Use caution in patients with known QT prolongation or those taking QT-prolonging drugs, although clinically relevant QT prolongation has not been shown at therapeutic doses.

🧠 Interaction pearl: Do not phrase this as “reduce mirabegron dose with CYP2D6 inhibitors.” The more important point is that mirabegron itself inhibits CYP2D6, so it can raise levels of some CYP2D6 substrates.

⚠️ Cautions

• Hypertension: mirabegron can increase blood pressure.
• Measure BP before starting treatment and monitor regularly during treatment.
• Use caution in patients with stage 2 hypertension, for example BP ≥160/100 mmHg.
• Renal impairment: dose reduction or avoidance may be required.
• Hepatic impairment: dose reduction or avoidance may be required.
• Bladder outlet obstruction: use cautiously because of urinary retention risk.
• Combination with antimuscarinics: use cautiously, particularly in patients at risk of urinary retention.
• Known QT prolongation / QT-prolonging drugs: use caution.

⛔ Contraindications

• ❌ Severe uncontrolled hypertension: systolic BP ≥180 mmHg and/or diastolic BP ≥110 mmHg.
• ❌ Hypersensitivity to mirabegron or any excipients.
• ❌ Avoid in severe hepatic impairment.
• ❌ Avoid in end-stage renal disease or dialysis unless specialist advice supports use.

🤰 Pregnancy / Breastfeeding

• Pregnancy: avoid unless clearly necessary; check BNF/specialist advice.
• Breastfeeding: check BNF or specialist advice before use.

🤒 Side Effects

• 📈 Hypertension.
• ❤️ Tachycardia, palpitations, arrhythmias, including atrial fibrillation.
• 🦠 Urinary tract infection.
• 🤢 Nausea or dyspepsia.
• 💩 Constipation or diarrhoea.
• 😵 Headache or dizziness.
• 😣 Rash, pruritus, or hypersensitivity reactions.
• 🚽 Urinary retention, particularly in patients with bladder outlet obstruction or when combined with antimuscarinic medicines.

🧓 Frailty / Older Adult Prescribing Pearls

• Mirabegron can be helpful when avoiding anticholinergic burden is important.
• Before prescribing, look for reversible causes of urinary urgency or frequency:
  • UTI
  • Glycosuria / uncontrolled diabetes
  • Constipation
  • Excess caffeine or alcohol
  • Diuretics or poorly timed diuretic dosing
  • Reduced mobility or delayed toileting access
  • Atrophic urogenital symptoms
• In frail patients, always balance symptom benefit against BP rise, falls risk from nocturia, polypharmacy, and renal function.

🧠 Clinical Pearls

• Mirabegron treats overactive bladder by improving the storage phase of micturition rather than by blocking bladder muscarinic receptors.
• It is less likely than antimuscarinics to cause dry mouth, constipation, blurred vision, or cognitive adverse effects.
• The main monitoring issue is blood pressure.
• Do not start if BP is in the severe uncontrolled range: ≥180 systolic and/or ≥110 diastolic.
• Review response after an adequate trial and stop if ineffective.

📚 References

• BNF – Mirabegron
• NICE CKS: Mirabegron prescribing information
• NICE CKS: LUTS in men - Mirabegron prescribing information
• MHRA Drug Safety Update: Mirabegron and severe hypertension
• NHS: How and when to take mirabegron