Methacholine

Summary

Methacholine is a muscarinic agonist primarily used clinically in asthma challenge tests due to its ability to induce bronchospasm and dyspnea. A strong bronchospastic response at a low dose of methacholine indicates high airway reactivity, confirming a diagnosis of asthma.

Key Points

• Methacholine
  • Mechanism
    • Muscarinic agonist (cholinomimetic)
      • Typically administered in inhaled formulation
      • Targets M3 receptors in the bronchioles
  • Clinical Use
    • Asthma challenge (diagnostic test)
      • Stimulation of M3 receptors causes bronchoconstriction and mucus production
      • Overreactivity of airways to very small doses of methacholine suggests diagnosis of asthma (called “methacholine challenge test” or “bronchoprovocation test”)
  • Adverse Effects
    • Bronchospasm, dyspnea (obvious)