Iretig (Mirabegron)

Mirabegron is used to manage symptoms of the overactive bladder syndrome.

• Overactive bladder: reduces urgency episodes, increases functional bladder capacity, and improves overall urinary control.
• Urinary urgency: lessens the sudden, compelling need to void, allowing patients to postpone bathroom visits.
• Urinary frequency: decreases the number of daytime voids, contributing to better quality of life.
• Urge urinary incontinence: helps prevent involuntary leakage associated with sudden urges.

• Mirabegron selectively activates β3‑adrenergic receptors located on detrusor smooth muscle in the bladder. Stimulation of these receptors triggers a cascade that increases cyclic AMP levels, leading to relaxation of the detrusor during the storage phase of the micturition cycle. This relaxation expands functional bladder capacity and reduces involuntary contractions, thereby alleviating urgency, frequency, and urge incontinence associated with overactive bladder.

Adverse reactions reported with mirabegron include both common and less frequent events.

Common Side Effects

• Headache: mild to moderate head pain that may appear within the first weeks of treatment.
• Elevated blood pressure: increase in systolic or diastolic pressure, often monitored during therapy.
• Nasopharyngitis: cold‑like symptoms such as sore throat, nasal congestion, and mild cough.

Serious or Rare Side Effects

• Severe hypertension: marked rise in blood pressure that can lead to cardiovascular complications and may require medication adjustment.
• Acute urinary retention: sudden inability to void, potentially necessitating catheterisation or emergency medical care.
• Anaphylactic reaction: rare systemic allergic response presenting with rash, swelling, difficulty breathing, and hypotension.

Key safety considerations for mirabegron include the following precautions.

• Assess cardiovascular status: measure baseline blood pressure and continue regular monitoring during therapy.
• Review concomitant anticholinergic use: avoid additive urinary side effects and consider dose adjustments.
• Evaluate renal function: adjust dosage or frequency in patients with moderate to severe renal impairment.
• Evaluate hepatic function: use with caution in patients with moderate or severe liver disease.
• Pregnancy and lactation: safety not established; prescribe only when potential benefit justifies potential risk.
• Store at ambient temperature: keep in original container, protect from moisture and light, and do not expose to extreme heat.

Mirabegron may interact with several medicines; the following interactions are recognised.

Major Interactions (Avoid)

• Strong CYP2D6 inhibitors: may increase mirabegron plasma concentrations, raising risk of adverse effects.
• Narrow‑gap antihypertensives (e.g., beta‑blockers): combined effect can lead to excessive blood pressure reduction.
• QT‑prolonging agents: additive risk of cardiac arrhythmias.

Moderate Interactions (Monitor Closely)

• Diuretics: may affect fluid balance and blood pressure, requiring closer observation.
• Anticholinergic agents: may diminish therapeutic benefit on bladder symptoms.
• Other β‑agonists: additive sympathomimetic effects may increase heart rate or blood pressure.