Which medication class is a beta-3 adrenergic agonist?

Which medication class is a beta-3 adrenergic agonist?

• A. Tolterodine
• B. Oxybutynin
• C. Mirabegron
• D. Imipramine

Answer: (C)

Beta-3 adrenergic agonists relax the detrusor smooth muscle of the bladder during the filling phase, increasing storage capacity and reducing urgency and frequency. Mirabegron is the selective beta-3 receptor agonist used for overactive bladder; by activating these receptors on detrusor muscle, it raises cAMP within the cells, causing relaxation and allowing the bladder to hold more urine between voids. This mechanism directly targets storage symptoms without primarily blocking acetylcholine at muscarinic receptors, which is what the other drugs do. Tolterodine and oxybutynin are antimuscarinics that reduce detrusor contractions by blocking muscarinic receptors (mainly M3), leading to decreased bladder activity but with anticholinergic side effects. Imipramine is a tricyclic antidepressant with anticholinergic effects, not a beta-3 agonist.

Beta-3 adrenergic agonists relax the detrusor smooth muscle of the bladder during the filling phase, increasing storage capacity and reducing urgency and frequency. Mirabegron is the selective beta-3 receptor agonist used for overactive bladder; by activating these receptors on detrusor muscle, it raises cAMP within the cells, causing relaxation and allowing the bladder to hold more urine between voids. This mechanism directly targets storage symptoms without primarily blocking acetylcholine at muscarinic receptors, which is what the other drugs do. Tolterodine and oxybutynin are antimuscarinics that reduce detrusor contractions by blocking muscarinic receptors (mainly M3), leading to decreased bladder activity but with anticholinergic side effects. Imipramine is a tricyclic antidepressant with anticholinergic effects, not a beta-3 agonist.