Methacholine chloride is used in the bronchial provocation test to assess airway hyperresponsiveness in patients suspected of having asthma. Its pharmacological basis is that it is a:

• A Beta-2 receptor agonist that relaxes bronchial smooth muscle
• B Cholinesterase inhibitor that prolongs endogenous acetylcholine action
• C Muscarinic receptor agonist resistant to acetylcholinesterase that induces bronchoconstriction ✓
• D Histamine H1 receptor partial agonist with prolonged bronchoconstrictor action

Explanation

Methacholine is a synthetic choline ester and direct muscarinic agonist. The addition of a methyl group at the beta carbon makes it highly resistant to acetylcholinesterase, giving it a longer duration of action than acetylcholine, and its strong M3 mediated contraction of bronchial smooth muscle provokes airflow limitation in hyperreactive airways. It is neither a beta-2 agonist nor an enzyme inhibitor, and histamine is a separate provocative agent.

Reference: Katzung's Basic and Clinical Pharmacology, 15th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.