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[Pharmacology](https://durgical.com/en/pharmacology/) · Class

# Beta-2 adrenergic agonists

Bronchodilators that stimulate the beta-2 receptor of airway muscle. Short-acting ones relieve attacks; long-acting ones keep airways open for hours.

Updated 2026-11-01

## What they are

Agonists of the beta-2 adrenergic receptor, the main bronchodilators for asthma and COPD. Short-acting agents (SABA: salbutamol, terbutaline) are relievers for sudden symptoms and for exercise-induced bronchospasm. Long-acting agents (LABA: salmeterol, formoterol; once-daily indacaterol, vilanterol, olodaterol) are maintenance treatment; in asthma a LABA is always given with an inhaled corticosteroid.

## Mechanism of action

The beta-2 receptor is a Gs-coupled receptor. Activation stimulates adenylyl cyclase and raises cyclic AMP; protein kinase A then lowers intracellular calcium and the activity of myosin light-chain kinase, so airway smooth muscle relaxes whatever the constricting stimulus. Cyclic AMP also reduces mediator release from mast cells. Beta-2 receptors in the heart, skeletal muscle and liver explain tachycardia, tremor, hypokalaemia and hyperglycaemia.

Target: Beta-2 adrenergic receptor (ADRB2), a Gs-coupled receptor

## Key points

- SABA = reliever; LABA = controller. Needing the reliever more often is a sign that asthma is getting worse.
- In asthma a LABA is never given alone: LABA monotherapy raises the risk of serious asthma-related events; with an inhaled corticosteroid it does not.
- Systemic effects: tremor, tachycardia, palpitations, hypokalaemia and hyperglycaemia; these add up with diuretics and theophylline.
- Beta blockers (even eye drops) can block the effect and trigger severe bronchospasm in asthma.
- Formoterol acts within minutes; salmeterol has a slower onset, so it is never a reliever.

## Drugs in this class

- [**Salbutamol** The classic reliever inhaler: a short-acting beta-2 agonist that opens the airways within minutes during an asthma or… Beta-2 adrenergic receptor](https://durgical.com/en/pharmacology/salbutamol/)
- [**Formoterol** A long-acting beta-2 agonist that also works within minutes. Maintenance bronchodilator in COPD; in asthma only with… Beta-2 adrenergic receptor](https://durgical.com/en/pharmacology/formoterol/)
- [**Salmeterol** A long-acting beta-2 agonist with a slow onset, used twice a day. In asthma it is always combined with an inhaled… Beta-2 adrenergic receptor](https://durgical.com/en/pharmacology/salmeterol/)
- [**Terbutaline** A short-acting beta-2 agonist given by injection, tablet or inhaler for bronchospasm. Its boxed warning forbids… Beta-2 adrenergic receptor](https://durgical.com/en/pharmacology/terbutaline/)

## Others in the class

- Indacaterol
- Vilanterol
- Olodaterol
- Levosalbutamol

## Test yourself

Think of the answer, then tap the question to see it.

## Through which second messenger does a beta-2 agonist relax airway smooth muscle?

Cyclic AMP: the Gs-coupled receptor activates adenylyl cyclase, and protein kinase A lowers calcium and myosin light-chain kinase activity.

## Why is a LABA never used alone in asthma?

LABA monotherapy increases serious asthma-related events, including death; combined with an inhaled corticosteroid this risk does not rise significantly.

## Which electrolyte falls with high doses of beta-2 agonists, and why?

Potassium: beta-2 stimulation shifts potassium into cells, which may cause hypokalaemia and ECG changes.

## Which drug group can block a beta-2 agonist and cause severe bronchospasm in asthma?

Beta blockers, especially non-selective ones, including eye drops.

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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 - ALBUTEROL SULFATE HFA- albuterol sulfate aerosol, metered](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=7bb5b6dd-9105-4ee7-b205-ed79cf4b371b) (DailyMed (U.S. National Library of Medicine), 2023); [DailyMed - FORMOTEROL FUMARATE solution](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=07afdf7e-c480-4806-b469-a6a460522bc0) (DailyMed (U.S. National Library of Medicine), 2025); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 44 (McGraw Hill, 2023).

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