A pulmonologist performs a bronchoprovocation test using increasing concentrations of a cholinergic agonist delivered by nebulizer to assess airway hyperresponsiveness in suspected asthma. Which drug is used and via which receptor does it act?
- A Bethanechol, acting on oesophageal M3 receptors
- B Carbachol, acting on ganglionic Nn receptors
- C Methacholine, acting on bronchial M3 receptors ✓
- D Pilocarpine, acting on airway M2 receptors
Correct answer: C. Methacholine, acting on bronchial M3 receptors
Explanation
Methacholine is the standard agent for bronchial provocation testing because it is a muscarinic agonist with predominantly M3-mediated bronchoconstrictor action and negligible nicotinic activity. C positive test is a fall in FEV1 of 20 percent or more at a provocative concentration. Carbachol has significant nicotinic activity making it unsuitable, bethanechol is used for bladder and gut atony, and pilocarpine acts mainly on sweat glands and the eye.
Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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