Mirabegron, a beta-3 adrenergic agonist used for overactive bladder, exerts its therapeutic effect primarily by which mechanism?

• A Inhibiting acetylcholine release from parasympathetic nerve terminals
• B Blocking M3 receptors on detrusor smooth muscle
• C Relaxing detrusor smooth muscle via cAMP-mediated pathway ✓
• D Increasing sympathetic tone to the internal urethral sphincter

Explanation

Beta-3 adrenoceptors are the predominant beta-adrenergic subtype in the detrusor muscle. Mirabegron activates them, leading to adenylyl cyclase stimulation, increased cAMP, and protein kinase A activation, which phosphorylates myosin light chain kinase and causes detrusor relaxation during the filling phase. This mechanism avoids the dry mouth and constipation of antimuscarinic agents. Options A and C describe the mechanisms of botulinum toxin and antimuscarinics respectively.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.