Describe the mechanism of action of mirabegron and a potential cardiovascular side effect to monitor.

• A. Beta-3 adrenergic receptor agonist that relaxes the detrusor during storage; can cause increased blood pressure, tachycardia; monitor BP and heart rate
• B. Muscarinic antagonist used to reduce bladder contractions
• C. Alpha-1 blocker causing orthostatic hypotension
• D. Diuretic increasing urine production

Answer: (A)

Mirabegron activates beta-3 adrenergic receptors in the detrusor muscle of the bladder, causing relaxation of the detrusor during the storage phase and increasing bladder capacity to reduce urgency and incontinence. Because it works through beta receptors systemically, there is a risk of increased blood pressure and tachycardia, so monitor blood pressure and heart rate regularly, especially when starting or adjusting the dose. Other bladder drugs work by different mechanisms (for example, muscarinic antagonists reduce bladder contractions, while alpha-1 blockers or diuretics have different systemic effects), but the key point here is the beta-3–mediated relaxation of the detrusor and the potential cardiovascular monitor needs.