Iretig (Mirabegron)

Mirabegron is indicated for conditions affecting bladder storage function in the overactive bladder disease family.

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

• Mirabegron selectively stimulates β3‑adrenergic receptors located on detrusor smooth‑muscle cells in the bladder. Activation of these receptors increases intracellular cyclic adenosine monophosphate (cAMP), leading to relaxation of the detrusor during the storage phase. The resulting reduction in bladder muscle tone expands functional bladder capacity and diminishes involuntary contractions that cause urgency and incontinence. Additionally, the drug’s selectivity minimizes activation of β1 and β2 receptors, reducing cardiovascular side effects.

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

Common Side Effects

• Hypertension: increased blood pressure.
• Headache: mild to moderate head pain.
• Nasopharyngitis: inflammation of the nasal passages and throat.
• Constipation: reduced bowel movements.

Serious or Rare Side Effects

• Severe hypertension: markedly elevated blood pressure requiring medical intervention.
• Urinary retention: difficulty emptying the bladder.
• Angioedema or anaphylaxis: rapid swelling of face, lips, tongue or severe allergic reaction.

When prescribing Mirabegron, clinicians should consider several precautionary measures to ensure patient safety.

• Monitor blood pressure: check baseline and periodic measurements during therapy.
• Assess cardiovascular status: avoid use in patients with uncontrolled hypertension or recent cardiac events.
• Evaluate renal function: dose adjustment may be needed in severe renal impairment.
• Review hepatic function: consider dose reduction in moderate to severe liver disease.
• Caution with drug interactions: avoid concomitant strong CYP2D6 inhibitors without dose adjustment.
• Store at room temperature: keep in the original container, protect from moisture and light.

Mirabegron can affect the pharmacokinetics of several co‑administered medicines, leading to clinically relevant interactions.

Major Interactions (Avoid)

• Strong CYP2D6 inhibitors (e.g., paroxetine, fluoxetine): may increase mirabegron plasma levels.
• Antihypertensive agents (e.g., β‑blockers, ACE inhibitors): mirabegron may reduce their blood‑pressure‑lowering effect.

Moderate Interactions (Monitor Closely)

• CYP3A4 inhibitors (e.g., ketoconazole, erythromycin): may modestly raise mirabegron concentrations.
• CYP3A4 inducers (e.g., rifampicin, carbamazepine): may lower mirabegron exposure.
• Digoxin: mirabegron can increase digoxin serum levels.
• NSAIDs: combined use may enhance risk of hypertension.