Salbutamol is a short-acting, highly selective β2-adrenergic stimulant, used in the treatment of bronchial asthma and other forms of reversible airways obstructive diseases. Salbutamol is rapidly absorbed after oral administration and undergoes presystemic metabolism in the gut, oral bioavailability is 50%. After inhalation, the systemic levels of salbutamol are low due to its gradual absorption from the bronchi. Overall duration of action of salbutamol is 4-6 hours.
Mechanism of action of salbutamol:
Salbutamol stimulate β2 adrenergic receptors which are predominant receptors in bronchial smooth muscle (β2-receptors are present in human heart in a concentration between 10% and 50%, and also present in the others part of the body). 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 increase of cyclic AMP relaxes bronchial smooth muscle and decrease airway resistance by lowering intracellular ionic calcium concentrations. Salbutamol relaxes the smooth muscles of airways, from trachea to terminal bronchioles.
Increased cyclic AMP concentrations are also inhibits the release of bronchoconstrictor mediators such as histamine, leukotreine from the mast cells in the airway.
Salbutamol has more effect on the respiratory tract, in the form of bronchial smooth muscle relaxation at recommended doses while producing fewer cardiovascular effects.
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 bronchitis
2. Exercise-Induced Bronchospasm:
Salbutamol is used for the prevention of exercise-induced 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 and dosage of salbutamol:
Salbutamol is available as tablet, syrup, metered dose inhaler (MDI), dry powder inhaler (DPI), nebulised solution and intramuscular or intravenous injectable form that may be given as following dosage:
- 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.
- One puff (100 mcg) to two puffs (200 mg) of salbutamol metered dose inhaler (MDI) or one capsule (200 mcg) to two capsules (400 mcg) of salbutamol dry powder inhaler (DPI) is inhaled as need basis.
- 1 to 2 ml of salbutamol nebulised 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.
- 5 to 10 ml (each ml contain 50 mcg) of salbutamol injection is used intramuscularly or intravenously in severe acute attack.
Side effects of salbutamol:
Serious side effects of salbutamol are a few. The common side effects of salbutamol are palpitation, chest discomfort, tremor, headache, muscle cramps, hypokalemia, difficulty in micturition, hypersensitivity reactions and paradoxical bronchospasm. [Read details]
There are two types of salbutamol inhaler present, one is salbutamol HFA inhaler and another is salbutamol dry powder inhaler (DPI).
(1) Salbutamol HFA inhaler: It is a pressurized metered-dose aerosol inhaler (MDI). 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. [Read details]
(2) Salbutamol dry powder inhaler (DPI): It is present 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. [Read details]
Symptoms of salbutamol overdose are palpitation, tachycardia, arrhythmias, angina, hypertension, dizziness, tremor, seizures, nervousness, headache, fatigue, malaise, sleeplessness, dry mouth etc. Overdose may cause cardiac arrest and even death. Treatment is discontinuation of salbutamol together with appropriate symptomatic management. The judicious use of cardioselective beta-blocker may be helpful in this setting but bearing in mind that such beta-blocker may produce bronchospasm.