methacholine methacholine methacholine (inn, usan) (trade name provocholine), also known as acetyl-β-methylcholine, is a synthetic choline ester that acts as a non-selective muscarinic receptor agonist in the parasympathetic nervous system. methacholineclinical datatrade namesprovocholineahfs/drugs.comconsumer drug informationlicense data us dailymed: methacholine routes ofadministrationrespiratoryatc codev04cx03 (who) legal statuslegal status au: s4 (prescription only) us: ℞-only identifiers iupac name 2-(acetyloxy)-n,n,n-trimethylpropan-1-aminium cas number55-92-5 n 62-51-1 (chloride)pubchem cid6114drugbankdb06709 ychemspider5888 yunii03v657zd3vkeggd04970 ychebichebi:50142 ychemblchembl978 ncomptox dashboard (epa)dtxsid2046967 chemical and physical dataformulac8h18no2+molar mass160.237 g·mol−13d model (jsmol)interactive image smiles .o=c(oc(c)c(c)(c)c)c inchi inchi=1s/c8h18no2.clh/c1-7(11-8(2)10)6-9(3,4)5;/h7h,6h2,1-5h3;1h/q+1;/p-1 ykey:jhphvavfuytvcl-uhfffaoysa-m y ny (what is this?) (verify) medical uses methacholine is primarily used to diagnose bronchial hyperreactivity, which is the hallmark of asthma and also occurs in chronic obstructive pulmonary disease. this is accomplished through the bronchial challenge test, or methacholine challenge, in which a subject inhales aerosolized methacholine, leading to bronchoconstriction. other therapeutic uses are limited by its adverse cardiovascular effects, such as bradycardia and hypotension, which arise from its function as a cholinomimetic. pharmacology it is highly active at all of the muscarinic receptors, but has little effect on the nicotinic receptors. methacholine has a charged quaternary amine structure, rendering it insoluble to lipid cell membranes. clinically, this means that it will not cross the blood–brain barrier and has poor absorption from the gastrointestinal tract. it is broken down at a relatively slow rate within the body, due to its relative resistance to acetylcholinesterases. the chemical structure of methacholine is identical to acetylcholine but with a methyl group on the beta carbon (hence being called acetyl-β-methylcholine), this β-methyl group provides selectivity towards muscarinic receptors as compared to nicotinic receptors. the quaternary ammonium group is essential for activity. the ester makes it susceptible to the enzyme acetylcholine esterase. contraindications use of methacholine is contraindicated in patients with recent heart attack or stroke, uncontrolled hypertension, known severe airway disease, or an aortic aneurysm. it may be used with caution by nursing or pregnant mothers and patients taking certain medications for myasthenia gravis.