Clinical pharmacology
Salbutamol is a direct-acting sympathomimetic with predominantly, Beta-adrenergic activity and a selective action on beta2 receptors. This results in its bronchodilating action being more prominent than its effect on the receptors in bronchial smooth muscle produce bronchodilation when stimulated. This makes salbutamol a short-acting selective agonist of beta2-adrenoceptors (beta2 agonist; beta2 stimulants)
Pharmacokinetics
Salbutamol is readily absorbed from the gastro-intestinal tract. It is subject to first-pass metabolism in the liver and possibly in the gut wall; the main metabolite is an inactive sulphate conjugate. It is rapidly excreted in the urine as metabolites and unchanged drug; there is some excretion in the faeces. The plasma half-life of salbutamol has been estimated to range from 4 to 6 hours.
Uses
Salbutamol is used as bronchodilators in the management of reversible airways obstruction, as in asthma and in some patients with chronic obstructive pulmonary disease. Salbutamol also decreases uterine contractility and may be given as the sulphate to arrest premature labour
Dosage and administration
Adults: Salbutamol may be given by mouth in dose of 2 to 4mg three or four times daily; some patients may require doses of up to 8mg three to four times daily. If adequate bronchodilation is not obtained with 4 mg each single dose could be gradually increased to as much as 8 mg
In elderly patients it is advisable to initiate treatment at the lower dose of 2mg three or four times a day and increase gradually as necessary.
Children: the following doses could be administered 3 or 4 times per day. As the drug is well-tolerated by children, the dose may be increased when it is appropriate
2 to 6 years: 1 to 2mg
6 to 12 years: 2 mg
Over 12 years: 2 to 4 mg
Precautions
Salbutamol and other Beta Agonists should be given with caution in hyperthyroidism, myocardial insufficiency, arrhythmias, susceptibility to QT-interval prolongation, hypertension and diabetes mellitus. In severe asthma particular caution is also required to avoid inducing hypokalaemia as this effect may be potentiated by hypoxia or by concomitant use of other anti-asthma drugs; plasma potassium concentration should be monitored.
Adverse effects
Salbutamol may cause fine tremor of skeletal muscle (particularly the hands), palpitations and muscle cramps. Tachycardia, nervous tension, headaches and peripheral vasodilation and rarely muscle cramps have been reported after large doses as has potentially serious hypokalaemia. Hypersensitivity reactions have occurred including paradoxical bronchospasm, angioedema, urticarial, hypotension and collapse
Interactions
Use of salbutamol and other beta agonists with corticosteroids, diuretics or xanthines increases the risk of hypokalaemia and monitoring of potassium concentrations is recommended in severe asthma, where such combination therapy is the rule
