Introduction
Adrenaline (Epinephrine) is a potent sympathomimetic agent used in emergencies such as anaphylaxis, cardiac arrest, and severe asthma. It stimulates alpha, beta-1, and beta-2 adrenergic receptors, producing widespread effects on the cardiovascular and respiratory systems.
Pharmacokinetics
Adrenaline is rapidly inactivated in the liver by COMT and MAO. When administered intravenously, it has a very short half-life (about 2-3 minutes) and must be given continuously in critical situations. It is excreted primarily via the urine as metabolites.
Mechanism of Action
Adrenaline stimulates alpha-1 receptors, causing vasoconstriction, beta-1 receptors, leading to increased heart rate and contractility, and beta-2 receptors, resulting in bronchodilation and vasodilation in skeletal muscle.
Pharmacodynamics
Adrenaline increases cardiac output, raises blood pressure, dilates bronchioles, and helps to counteract the effects of severe allergic reactions. It also improves coronary and cerebral perfusion during resuscitation.
Adverse Effects
Tachycardia and Arrhythmias: Adrenaline can cause significant increases in heart rate and arrhythmias.
Hypertension: Excessive vasoconstriction may lead to dangerously high blood pressure.
Anxiety and Tremors: CNS stimulation may cause anxiety, tremors, and agitation.
Hyperglycemia: Adrenaline can increase blood glucose levels by promoting glycogenolysis.
Drug Interactions
Beta-blockers: Beta-blockers may exacerbate the alpha-adrenergic effects of adrenaline, causing unopposed vasoconstriction.
MAO inhibitors: Co-administration with MAO inhibitors may cause exaggerated pressor effects.
Dosages
Adults (Anaphylaxis): 0.3-0.5 mg intramuscularly, repeated every 5-15 minutes if necessary.
Cardiac Arrest: 1 mg intravenously every 3-5 minutes during resuscitation.