Pharmacology · Class
Inhaled antimuscarinics !
Inhaled blockers of the muscarinic receptor that open the airways by cutting vagal tone. A mainstay of COPD; tiotropium is also added in severe asthma.
Updated 2026-11-01
What they are
Quaternary ammonium antagonists of muscarinic receptors given by inhalation. The short-acting agent (SAMA) is ipratropium; long-acting agents (LAMA: tiotropium, umeclidinium, aclidinium, glycopyrronium) are maintenance bronchodilators in COPD and reduce its exacerbations. They are often combined with a beta-2 agonist.
Mechanism of action
Vagal nerves release acetylcholine onto M3 receptors of airway smooth muscle and glands, which causes bronchoconstriction and mucus secretion. Blocking M3 removes this cholinergic tone; the effect is larger in COPD, where vagal tone is the main reversible part of the obstruction. Being quaternary, these drugs are poorly absorbed and barely cross the blood-brain barrier, so systemic effects are few.
Target: Muscarinic acetylcholine receptor M3 (CHRM3) of airway smooth muscle
Drugs in this class
- Ipratropium bromideA short-acting inhaled antimuscarinic that opens the airways by blocking acetylcholine. Used in COPD, often together…Muscarinic acetylcholine receptor M3
- Tiotropium bromideA long-acting inhaled antimuscarinic used once a day in COPD. It keeps the airways open and reduces flare-ups; it is…Muscarinic acetylcholine receptor M3
Others in the class
- Umeclidinium
- Aclidinium
- Glycopyrronium
Test yourself
Think of the answer, then tap the question to see it.
Why do inhaled antimuscarinics cause few central nervous system effects?
They are quaternary ammonium compounds: permanently charged, poorly absorbed and barely able to cross the blood-brain barrier.
Which two conditions call for caution with inhaled antimuscarinics?
Narrow-angle glaucoma and urinary retention (prostatic hyperplasia or bladder-neck obstruction).
Why are antimuscarinics especially useful in COPD?
Vagal cholinergic tone is the main reversible component of airway narrowing in COPD, and long-acting agents also cut exacerbations.
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - TIOTROPIUM BROMIDE capsule (DailyMed (U.S. National Library of Medicine), 2025); DailyMed - IPRATROPIUM BROMIDE solution (DailyMed (U.S. National Library of Medicine), 2026); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 44 (McGraw Hill, 2023).
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Representative model, for educational purposes only.