Salbutamol

Salbutamol
(R,S)-2-(1,1-dimethylethyl)amino- 1-(4-hydroxy-3-hydroxymethylphenyl)ethanol
Empirical formula	C13H22N1O5
Molecular weight	239.3
Bioavailability (Oral)	"well absorbed"
Metabolism	hepatic
Elimination half life (Oral/inhaled)	2.7-5 hours
Excretion	renal
Pregnancy category	A (Australia)

Salbutamol (INN) or albuterol (USAN) is a short-acting β₂-adrenergic receptor agonist used for the relief of bronchospasm in conditions such as asthma and COPD. It is marketed by the Allen & Hanbury's respiratory division of GlaxoSmithKline under the trade name Ventolin. The name Albuterol comes from Salbutamol aersol.

Salbutamol sulfate is usually given by the inhaled route for direct effect on bronchial smooth muscle. This is usually achieved through a metered-dose inhaler (MDI) or nebuliser; but other delivery devices marketed for salbutamol sulfate include the Rotahaler, Diskhaler, and Autohaler. Salbutamol can also be given orally or intravenously.

Ventolin became available in the United Kingdom in 1969 and in the United States in 1980.

Clinical use

Salbutamol is specifically indicated in the following conditions:

• acute asthma
• symptom relief during maintenance therapy of asthma and other conditions with reversible airways obstruction (including COPD)
• protection against exercise-induced asthma
• certain conditions involving hyperkalemia

As a β₂-agonist, salbutamol also finds use in obstetrics. Intravenous salbutamol can be used as a tocolytic to relax the uterine smooth muscle to delay premature labour. Whilst preferred over agents such as atosiban and ritodrine, its role has largely been replaced by the calcium-channel blocker nifedipine which is more effective, better tolerated and orally effective. (Rossi, 2004)

Mode of action

As with other β₂-adrenergic receptor agonists, salbutamol binds to β₂-adrenergic receptors with a higher affinity than β₁-receptors. In the airways, activation of β₂-receptors results in relaxation of bronchial smooth muscle. resulting in a widening of the airway (bronchodilation). Inhaled salbutamol sulfate has a rapid onset of action, providing relief within 5-15 minutes of administration.

In tocolysis, the activation of β₂-receptors results in relaxation of uterine smooth muscle, thus delaying labour.

Adverse effects

Whilst salbutamol is well-tolerated, particularly when compared with previous therapies such as theophylline, like all medications there exists the potential for adverse drug reactions to occur - especially when in high doses, or when taken orally or intravenously.

Common adverse effects include: tremor, palpitations and headache. (Rossi, 2004)

Infrequent adverse effects include: tachycardia, muscle cramps, agitation, hypokalemia, hyperactivity in children, and insomnia. (Rossi, 2004)

References

• Rossi S (Ed.) (2004). Australian Medicines Handbook 2004 (AMH). Adelaide: Australian Medicines Handbook. ISBN 0-9578521-4-2.