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Beta-agonists

β2– agonists

These act on β2 adrenoceptors on bronchial smooth muscle, causing dilation of the smooth muscle whatever the cause.
They are selective because they only target the β2 receptors (not β1) and thus do not act on the myocardium

Mechanism

Examples

Category
Drugs
Other names
Short acting (~3-6 hours)
Salbutamol
Ventolin
Terbutaline
Long acting (~8-12 hours)
Salmeterol
Oxis, foradile, foradil, atock
Short acting drugs are used PRN
Long acting drugs tend to be used twice a day in patients with severe disease – they are always used in combination with an inhaled corticosteroid – they should never be used alone.
Note that – with inhaled drugs, only 15% of the inhaled dose actually makes it to the lungs, the rest is mostly deposited on the back of the throat.
Salbutamol metered dose inhaler

Unwanted effects

When you give it in an inhaled from, the inhaled dose is usually 100μg of salbutamol. This, when you tell the patient to take two puffs as required, they have a dose of 200μg. Patients can take these two puffs up to 6-8 times a day – even more in an emergency! When you give nebulised salbutamol, you are often giving a dose of 2.5-5mg – thus 10-20x the dose of ‘2 puffs’ from the inhaler.

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