► Salbutamol is a short-acting, highly selective β2-adrenergic stimulant.
► The chemical name of salbutamol is 1-(4-hydroxy-3-hydroxymethylphenyl)-2-(t-butylamino)-ethanol sulfate, molecular formula is (C13H21NO3)2 • H2SO4 and molecular weight is 576.7.
► After oral administration, approximately 50% of salbutamol is absorbed from the intestinal tract with a slower onset of action, reaching a peak at about 2 hours after intake. After inhalation, salbutamol reaches the lungs directly and acts within 3-5 minutes with a peak at 15-20 minutes. Overall duration of action of salbutamol is 4-6 hours. It is metabolized in the intestinal tract and in the liver and is excreted via the urine. Learn more.
Mechanism of action of salbutamol
► Salbutamol stimulates β2 adrenergic receptors which are predominant receptors in bronchial smooth muscle of the lung. Stimulation of β2 receptors leads to the activation of enzyme adenyl cyclase that form cyclic AMP (adenosine-mono-phosphate) from ATP (adenosine-tri-phosphate). This high level of cyclic AMP relaxes bronchial smooth muscle and decreases airway resistance by lowering intracellular ionic calcium concentrations. Salbutamol relaxes the smooth muscles of airways, from trachea to terminal bronchioles.
► High level of cyclic AMP are also inhibits the release of bronchoconstrictor mediators such as histamine, leukotreine from the mast cells in the airway.
Indications and usage of salbutamol
1. Bronchospasm with reversible obstructive airway diseases
Salbutamol is indicated for the preventation or treatment of bronchospasm with reversible obstructive airway diseases such as
► Bronchial asthama
► Chronic obstructive pulmonary disease (COPD) which includes chronic bronchitis and emphysema
2. Exercise-induced bronchospasm
► Salbutamol is used for the prevention of exercise-induced bronchospasm.
3. Any other situations known to induce bronchospasm.
Contraindications of salbutamol
Salbutamol is contraindicated in persons with a history of hypersensitivity reaction (urticaria, angioedema, rash) to salbutamol, or any of its components. Salbutamol is also contraindicated in patients with pre-existing cardiac tachyarrhythmias.
Preparations of salbutamol
Salbutamol is available as tablet, syrup, metered dose inhaler (MDI), dry powder inhaler (DPI), nebulizer solution and intramuscular or intravenous injectable form.
► Tablet form– Each tablet contains 2 or 4 mg salbutamol or 8 mg extended release salbutamol.
► Syrup form– Each 5 ml syrup (one teaspoon) contains 2 mg salbutamol.
► Metered dose inhaler (MDI) – It contains salbutamol in a pressurized aerosol form. It is used by oral inhalation only. Each inhalation contains 100 mcg salbutamol in HFA (Hydrofluoroethane) propellant. HFA is an ozone benign, environment friendly, CFC free propellant. Learn more.
► Dry powder inhaler (DPI) – It presents in capsule form. Each capsule contains 200 mcg salbutamol in a dry powder form. This DPI capsule is used only by oral inhalation via an inhalation device. Learn more.
► Nebulizer solution – Each ml nebulizer solution contains 5 mg sabutamol.
► Injection form – Each ml injection contains 50 mcg sabutamol.
Dosage of salbutamol
Sabutamol may be given as following dosage:
► Oral form – The usual dose of oral salbutamol is 2 to 4 mg three times a day in adult and 1 to 2 mg three times a day in children.
► Metered dose inhaler (MDI) – One to two puffs (100 to 200 mg) of salbutamol metered dose inhaler is inhaled as need basis.
► Dry powder inhaler (DPI) – one to two capsules (200 to 400 mcg) of salbutamol dry powder inhaler is inhaled as need basis.
► Nebulizer solution – 1 to 2 ml of salbutamol nebulizer solution should be diluted with normal saline to final volume of 2-4 ml is inhaled from a nebulizer until aerosol generation ceases. It may be required repeated in severe acute attack.
► Injection form – 5 to 10 ml (each ml contain 50 mcg) of salbutamol injection is used intramuscularly or intravenously in severe acute attack.
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Side effects of salbutamol
Salbutamol is usually a well tolerated drug. The incidence and severity of its side effects depend on dosage and route of administration. Overall, serious side effects of salbutamol are unusal. A fine tremor of skeletal muscle especially in the hands and nervousness are the most common side effects of salbutamol. It may also causes palpitation, tachycardia, chest discomfort, headache, muscle cramps, hypokalemia, difficulty in micturition and paradoxical bronchospasm. Learn more.
Use in pregnancy
Salbutamol is a pregnancy category C drug. It should be used during pregnancy only if absolutely essential. During pregnancy, inhalation of salbutamol has particular advantage as the therapeutic action can be achieved without the requirement for such plasma concentration liable to have an effect on the fetus.
Use in nursing mothers
Salbutamol is probably excreted in human milk but the concentration is unknown. However, no adverse effects have been reported in the breast fed babies of mothers receiving salbutamol by inhalation.
Salbutamol is not recommended in children below two years of age.
Dose selection for an elderly person should be cautious. Salbutamol should be start at the low dosage, reflecting the greater frequency of decreased cardiac, kidney or liver function.
Precautions of salbutamol
Salbutamol should be used with caution in patients with cardiac arrhythmia, hypertension, hyperthyroidism, convulsive disorders and diabetes mellitus. It should be taken with extreme caution in persons taking tricyclic antidepressants, monoamine oxidase inhibitors, loop diuretics or thiazide diuretics. Beta-receptor blocking drugs should be avoided during salbutamol therapy because these drugs block the bronchodilator effect of salbutamol. Learn more.
Overdose of salbutamol
The most common symptoms of overdose with salbutamol are tremor, palpitation and tachycardia. It may also produces arrhythmias, hypertension, angina, seizures, nervousness, fatigue, malaise, headache, dizziness, sleeplessness, dry mouth and even cardiac arrest.
Treatment is symptomatic with discontinuation of salbutamol is needed. A cardio-selective beta receptor blocking drug (atenolol, metoprolol) may be given by intravenous injection in patients presenting with tachycardia and palpitation. In general, beta receptor blocking drugs should be used cautiously as they may cause bronchospasm in sensitive persons. Hypokalaemia (decrease potassium level in the blood) may occur following overdose with salbutamol. Serum potassium level should be monitored.