Methacholine is a direct-acting muscarinic receptor agonist and a synthetic choline ester. It is primarily used as a bronchial challenge agent to assess airway hyperresponsiveness, particularly during diagnostic testing for asthma.
Methacholine is commonly supplied pharmaceutically as Methacholine Chloride, the chloride salt of methacholine. FDA's substance database identifies methacholine as the active form and methacholine chloride as its salt form.
Methacholine Chloride is a specialized respiratory diagnostic pharmaceutical API used in the manufacture of preparations for controlled bronchial provocation testing.
CAS Number: 62-51-1
Molecular Formula: C8H18ClNO2
Molecular Weight: 195.69 g/mol
Chemical Name: Methacholine Chloride
Synonyms: Acetyl-β-methylcholine chloride; (2-Acetoxypropyl)trimethylammonium chloride
Drug Class: Muscarinic Cholinergic Agonist
Therapeutic Class: Bronchial Challenge Agent
Therapeutic Area: Respiratory / Pulmonology
Molecule Type: Synthetic Small Molecule
USP defines Methacholine Chloride as containing 98.0%–101.0% of C8H18ClNO2 on an anhydrous basis.
Methacholine stimulates muscarinic acetylcholine receptors in airway smooth muscle. This produces bronchoconstriction and allows assessment of airway responsiveness during a controlled bronchial challenge test.
Methacholine Chloride is primarily associated with:
Methacholine Chloride is used in inhalation solutions/preparations for controlled bronchial challenge testing.
Methacholine Chloride is a white crystalline material. A pharmaceutical reference standard lists its melting point at approximately 171–173°C.
A controlled Methacholine Chloride manufacturing process may involve:
USP testing for Methacholine Chloride includes identification, assay, loss on drying, residue on ignition, heavy metals and limits for specified impurities.
| Parameter | Specification |
|---|---|
| Appearance | White crystalline powder or crystals |
| Identification | IR & HPLC compliant |
| Assay (HPLC) | 98.0% – 102.0% |
| Loss on Drying | NMT 1.5% |
| Residue on Ignition | NMT 0.5% |
| Heavy Metals | NMT 10 ppm |
| pH (1% Solution) | 2.0 – 4.0 |
| Individual Impurity | NMT 1.0% |
| Total Impurities | NMT 1.0% |
| Water Content | NMT 1.5% |
| Melting Point | 171–173°C |