A 58-year-old man with benign prostatic hyperplasia and overactive bladder is prescribed a muscarinic antagonist. Which agent has the highest selectivity for the M3 receptor in the bladder with minimal cognitive adverse effects due to poor CNS penetration?
- A Oxybutynin
- B Trospium ✓
- C Tolterodine
- D Darifenacin
Correct answer: B. Trospium
Explanation
Trospium is a quaternary ammonium compound that does not cross the blood-brain barrier, resulting in negligible CNS adverse effects (minimal risk of cognitive impairment or delirium), making it preferred in elderly patients. Darifenacin has M3 selectivity but does penetrate the CNS to some extent. Oxybutynin has significant CNS penetration and causes the most anticholinergic CNS adverse effects. Tolterodine is less M3-selective and has intermediate CNS penetration.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.