Mirabegron, used for overactive bladder, differs mechanistically from antimuscarinics such as oxybutynin because it acts as a:

• A M3 muscarinic receptor partial agonist with tissue selectivity
• B Beta-3 adrenoceptor agonist causing detrusor relaxation ✓
• C Alpha-1A adrenoceptor antagonist reducing bladder outlet resistance
• D NK2 receptor antagonist blocking substance-P-mediated detrusor contraction

Explanation

Mirabegron is a selective beta-3 adrenoceptor agonist; stimulation of beta-3 receptors in the detrusor muscle activates adenylyl cyclase, raising cAMP and relaxing the bladder during filling. Unlike antimuscarinics, mirabegron does not block muscarinic receptors, so it avoids dry mouth, constipation, cognitive impairment, and urinary retention in men. Its main adverse effect is hypertension due to mild beta-1/beta-2 effects and potential vascular beta-3 activity. This makes it preferred in elderly patients where anticholinergic burden is a concern.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.