Salbutamol

• Salbutamol is used in the treatment of asthma, chronic obstructive airways disease, and uncomplicated preterm labour.
• Salbutamol is a synthetic sympathomimetic amine.
• Salbutamol is available as 2/4/8 mg tablets, a syrup containing 0.4/2.5 mg/ml, an aerosol delivering 100 micrograms/puff, a dry powder for inhalation in capsules containing 200/400 micrograms, a solution for nebulization containing 2.5/5 mg/ml, and as a clear, colourless solution for injection containing 1 mg/ml of salbutamol sulfate.
• The main actions of salbutamol are bronchodilatation and uterine relaxation.
• Salbutamol is a beta-adrenergic agonist (with a more pronounced effect at beta-2 than beta-1 receptors) that acts by stimulation of membrane-bound adenylate cyclase in the presence of magnesium ions to increase intracellular cAMP concentrations.
• Salbutamol also directly inhibits antigen-induced release of histamine and slow-releasing substance of anaphylaxis from mast cells.
• The adult oral dose of salbutamol is 2–4 mg 6- to 8-hourly.
• One or two metered puffs of 200–400 micrograms of the powder may be inhaled 6- to 8-hourly; 2.5–5 mg of the nebulized solution may be inhaled similarly 6-hourly.
• The drug may also be administered subcutaneously or intramuscularly in a dose of 0.5 mg 4-hourly.
• Salbutamol should be administered intravenously as an infusion diluted in glucose or saline at a rate not exceeding 0.5 micrograms/kg/min.
• Bronchodilatation after the administration of salbutamol occurs 5–15 minutes after inhalation and 30 minutes after ingestion of the drug, and lasts for up to 4 hours.
• In high doses, the beta-1 actions of the drug lead to positive inotropic and chronotropic effects.
• At lower doses, the beta-2 effects predominate and cause a decrease in the peripheral vascular resistance, leading to a decrease in the diastolic blood pressure of 10–20 mmHg.
• Bronchodilatation, leading to an increased peak expiratory flow rate (PEFR) and FEV1, occurs after the administration of salbutamol.
• This is additive to the bronchodilatation produced by phosphodiesterase inhibitors.
• The drug interferes with the mechanism of hypoxic pulmonary vasoconstriction; an adequate inspired oxygen concentration should be ensured when the drug is used.
• Salbutamol decreases the tone of the gravid uterus; 10% of an administered dose crosses the placenta and may lead to tachycardia in the fetus.
• Salbutamol may decrease the plasma potassium concentration by causing a shift of the ion into cells.
• The drug may also cause an increase in the plasma concentrations of free fatty acids and glucose; insulin release is therefore stimulated.
• Anxiety, insomnia, tremor (with no attendant change in motor strength), sweating, palpitations, ketosis, lactic acidosis, hypokalaemia, postural hypotension, and nausea and vomiting may occur, following the use of the drug.
• In high doses, the beta-1 actions of the drug lead to positive inotropic and chronotropic effects.