Mirabegron

Mirabegron is used to treat conditions related to overactive bladder, a disorder of urinary storage.

• Overactive bladder: Improves bladder capacity and reduces episodes of urgency and incontinence.
• Urinary urgency: Decreases the frequency of sudden, compelling urges to void.
• Urinary frequency: Lowers the number of daytime voids.
• Urge urinary incontinence: Reduces involuntary leakage associated with sudden urges.

• Mirabegron selectively activates β3‑adrenergic receptors located on the detrusor smooth muscle of the bladder. This activation stimulates a cyclic AMP–mediated signaling cascade that leads to relaxation of the detrusor during the storage phase, thereby increasing functional bladder capacity and reducing involuntary contractions associated with overactive bladder. The drug does not significantly affect α‑adrenergic or muscarinic pathways, allowing it to act without anticholinergic side effects.

Mirabegron may cause a range of adverse reactions, which are categorized by frequency and severity.

Common Side Effects

• Hypertension: Elevated blood pressure observed in some patients.
• Nasopharyngitis: Mild upper respiratory tract infection symptoms.
• Headache: Persistent or intermittent head pain.
• Constipation: Reduced bowel movement frequency.
• Dry mouth: Decreased salivary secretion.
• Dizziness: Light‑headed sensation, especially on standing.

Serious or Rare Side Effects

• Cardiovascular events: Tachycardia, arrhythmia, or angina.
• Urinary retention: Difficulty initiating or maintaining urine flow.
• Severe hypersensitivity: Rash, angioedema, or anaphylaxis.
• Angle‑closure glaucoma: Acute increase in intra‑ocular pressure (rare).

Before initiating Mirabegron therapy, clinicians should consider several safety aspects.

• Assess blood pressure: Monitor baseline and periodically due to risk of hypertension.
• Review cardiovascular status: Use cautiously in patients with uncontrolled hypertension or severe cardiac disease.
• Evaluate renal function: Dose adjustment may be needed in severe renal impairment.
• Consider hepatic function: Use with caution in moderate to severe hepatic impairment.
• Pregnancy and lactation: Safety not established; avoid unless benefit outweighs risk.
• Store at ambient temperature: Keep below 25 °C, in original packaging, protected from moisture and light.

Mirabegron can interact with other medicines, requiring attention to avoid reduced efficacy or increased toxicity.

Major Interactions (Avoid)

• Strong CYP2D6 inhibitors (e.g., fluoxetine, paroxetine, quinidine): May increase mirabegron exposure and risk of adverse effects.
• Antihypertensive agents (e.g., beta‑blockers): May attenuate the blood‑pressure‑lowering effect of concomitant therapy.

Moderate Interactions (Monitor Closely)

• Diuretics: Potential additive increase in blood pressure.
• Anticholinergic agents: May increase risk of urinary retention.
• Digoxin: May raise serum digoxin concentrations, requiring monitoring.
• NSAIDs: May enhance risk of hypertension when used together.