What is the role of epinephrine (adrenaline) in treating anaphylaxis?

Mechanism of Action of Epinephrine in Anaphylaxis

Epinephrine is the primary life-saving medication for anaphylaxis, acting on both alpha and beta-adrenergic receptors to rapidly reverse the life-threatening pathophysiologic changes of anaphylaxis, with no substitute for its comprehensive effects. 1, 2

Alpha-Adrenergic Effects

• Increases vasoconstriction and peripheral vascular resistance, which helps counteract the hypotension that occurs during anaphylaxis 1
• Decreases mucosal edema, helping to reduce airway obstruction 1, 2
• Reduces vascular permeability, preventing the loss of intravascular fluid volume that contributes to shock 1

Beta-Adrenergic Effects

• Causes bronchial smooth muscle relaxation (β2 effect), alleviating bronchospasm, wheezing, and dyspnea 1
• Increases cardiac inotropy (contractility) and chronotropy (heart rate) (β1 effect), supporting cardiovascular function 2
• Relaxes smooth muscle of the gastrointestinal tract, genitourinary system, and other organs, relieving associated symptoms 1
• Inhibits further release of inflammatory mediators from mast cells and basophils (β2 effect), helping to halt the progression of the allergic reaction 2

Metabolic Effects

• Increases glycogenolysis and reduces glucose uptake by tissues 1
• Inhibits insulin release from the pancreas, resulting in hyperglycemia 1
• Increases blood lactic acid levels 1

Pharmacokinetics

• Has a rapid onset of action when administered parenterally 1
• Has a relatively short duration of action, which may necessitate repeated dosing in prolonged anaphylactic reactions 2
• Most effective when administered immediately after the onset of anaphylaxis symptoms 3

Clinical Application

• Intramuscular injection into the lateral thigh (vastus lateralis) is the preferred route for first-line treatment 2
• The recommended dose for adults is 0.3-0.5 mg of 1:1000 solution 4, 5
• For children, the recommended dose is 0.01 mg/kg, up to 0.3 mg 2, 5
• May need to be repeated after 5-15 minutes if symptoms persist or worsen 2
• 10-20% of patients may require more than one dose for symptom resolution 2

Common Pitfalls in Epinephrine Administration

• Delayed administration is associated with increased morbidity and mortality 4, 2
• Using antihistamines instead of epinephrine as first-line treatment is a dangerous practice 2
• Incorrect route of administration (subcutaneous instead of intramuscular) may delay onset of action 3
• Intravenous administration increases risk of adverse effects and should be reserved for severe cases under close monitoring 3, 2
• Underdosing in children due to fear of side effects 2
• Failure to carry or prescribe epinephrine autoinjectors for at-risk patients 2, 4

Epinephrine remains the cornerstone of anaphylaxis management, with its multi-system effects addressing the complex pathophysiology of this potentially fatal condition. No other medication provides the same comprehensive life-saving actions across multiple organ systems 6, 2.