Methacholine

Methacholine is a non-selective muscarinic receptor agonist that acts directly on airway smooth muscle receptors inducing bronchoconstriction with a longer mechanism of action compared to acetylcholine. It has limited therapeutic uses as its cholinomimetic effects can lead to bradycardia and hypotension. It is primarily used to assist in the diagnosis of asthma as its a bronchoconstrictor, it can used to assess bronchial hyperreactivity. The bronchoconstriction is more significant in patients with asthma than those without. Methacholine has been used in the treatment of glaucoma and Raynaud’s syndrome.

Methacholine challenge test (bronchoprovocation test):
This test is used to evaluate how “reactive” or “responsive” the lungs are when symptoms are suggestive of asthma, but it is not clearly clinically apparent. The test involves inhaling aerosolized methacholine which leads to bronchoconstriction. The test is considered positive if methacholine causes a 20 percent or greater decrease in breathing ability compared to the baseline as measured by before and after spirometry. A positive test suggests that the airways are “reactive” and a diagnosis of asthma should be considered.

Methacholine has a risk of severe bronchoconstriction in patients with a pre-existing reduced pulmonary function and clinically apparent asthma with wheezing, so is contraindicated for these people.

Trade name: Provocholine (marketed by Methapharm Inc)
Chemical Formula: C₈H₁₈NO₂

Other Cholinergic agonists:

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