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# 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

## Key points

- First-line bronchodilators in COPD; the long-acting ones also reduce exacerbations.
- Dry mouth is the most common effect; urinary retention and worsening of narrow-angle glaucoma are the classic cautions.
- Nebulised solution or powder in the eye causes blurred vision and pupil dilation: a mouthpiece is preferred to a face mask.
- Ipratropium is short-acting and often paired with salbutamol; tiotropium works for about a day.
- Tiotropium leaves M3 and M1 receptors slowly but M2 quickly (kinetic selectivity).

## Drugs in this class

- [**Ipratropium bromide** A short-acting inhaled antimuscarinic that opens the airways by blocking acetylcholine. Used in COPD, often together… Muscarinic acetylcholine receptor M3](https://durgical.com/en/pharmacology/ipratropium-bromide/)
- [**Tiotropium bromide** A 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](https://durgical.com/en/pharmacology/tiotropium-bromide/)

## 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.

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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](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=496b38ee-45b6-4bb2-a35e-9023c3b73719) (DailyMed (U.S. National Library of Medicine), 2025); [DailyMed - IPRATROPIUM BROMIDE solution](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=db8095db-d1fd-4099-9fb1-d1ad4e284976) (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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