From the Guidelines
Epinephrine is primarily effective for true allergic reactions (type I hypersensitivity reactions) rather than drug sensitivity reactions. In a true allergic reaction, especially anaphylaxis, epinephrine is the first-line treatment and should be administered promptly, typically as 0.01 mg/kg of a 1:1000 solution to a maximum of 0.5 mg in adults and 0.3 mg in children intramuscularly in the anterolateral thigh 1. Epinephrine works by constricting blood vessels to increase blood pressure, relaxing airway muscles to improve breathing, and reducing hives and swelling. For drug sensitivity reactions that are not true allergies (such as many rashes, delayed reactions, or non-IgE mediated responses), epinephrine is generally not indicated and other treatments like antihistamines, corticosteroids, or simply stopping the offending medication would be more appropriate. The distinction matters because inappropriate use of epinephrine carries risks including increased heart rate, anxiety, and potential cardiac complications, while withholding it during true anaphylaxis can be life-threatening.
Key Considerations
- The clinical criteria proposed by the National Institute of Allergy and Infectious Diseases (NIAID) provide a helpful framework in approaching patients with acute allergic symptoms 1.
- Risk factors for severe anaphylaxis include cardiovascular disease, asthma, older age, and additional coexisting, comorbid conditions 1.
- Epinephrine has a narrow toxic-therapeutic index and can cause mild transient adverse effects, but it is the cornerstone of anaphylaxis management and should be administered promptly 1.
- The optimal dosing interval for repeated epinephrine administration has not been studied prospectively, but it is recommended to repeat dosing as frequently as every 5 to 15 minutes if symptoms persist or worsen 1.
Administration and Dosage
- Epinephrine should be administered intramuscularly in the anterolateral thigh, with a dose of 0.01 mg/kg of a 1:1000 solution to a maximum of 0.5 mg in adults and 0.3 mg in children 1.
- The needle used for intramuscular injection should be of adequate length to reach the muscle beneath the subcutaneous adipose tissue over the vastus lateralis muscle 1.
Importance of Prompt Administration
- Delayed injection of epinephrine can be associated with poor outcomes, including fatality, emphasizing the need for prompt administration in cases of anaphylaxis 1.
From the FDA Drug Label
12 CLINICAL PHARMACOLOGY
12.1 Mechanism of Action Epinephrine acts on both alpha and beta-adrenergic receptors. 12. 2 Pharmacodynamics Through its action on alpha-adrenergic receptors, epinephrine lessens the vasodilation and increased vascular permeability that occurs during anaphylaxis, which can lead to loss of intravascular fluid volume and hypotension Through its action on beta-adrenergic receptors, epinephrine causes bronchial smooth muscle relaxation and helps alleviate bronchospasm, wheezing and dyspnea that may occur during anaphylaxis Epinephrine also alleviates pruritus, urticaria, and angioedema and may relieve gastrointestinal and genitourinary symptoms associated with anaphylaxis because of its relaxer effects on the smooth muscle of the stomach, intestine, uterus and urinary bladder
Epinephrine is indicated for the treatment of anaphylaxis, which is a true allergic reaction. The text does not explicitly differentiate between a drug hypersensitivity reaction and a true allergic (anaphylactic) reaction. However, it can be inferred that epinephrine is effective in treating symptoms associated with anaphylaxis, such as:
- Vasodilation and increased vascular permeability
- Bronchospasm, wheezing, and dyspnea
- Pruritus, urticaria, and angioedema Since the label specifically mentions anaphylaxis, it is reasonable to conclude that epinephrine is intended for the treatment of true allergic (anaphylactic) reactions. However, the label does not provide direct information on its effectiveness in drug hypersensitivity reactions that are not anaphylactic in nature 2.
From the Research
Epinephrine in Anaphylaxis and Hypersensitivity Reactions
- Epinephrine (adrenaline) is the primary treatment for anaphylaxis, a severe, life-threatening allergic reaction 3, 4, 5, 6, 7.
- It is essential to administer epinephrine promptly when anaphylaxis is suspected to minimize morbidity and mortality 3, 5, 7.
- Epinephrine autoinjectors are available for patients at risk of anaphylaxis and should be carried and used as directed 3, 4, 5, 7.
Difference between Anaphylaxis and Hypersensitivity Reactions
- Anaphylaxis is a specific type of severe allergic reaction that requires immediate treatment with epinephrine 3, 4, 5, 6, 7.
- Hypersensitivity reactions, on the other hand, may not always require epinephrine treatment, and the treatment approach may vary depending on the severity and type of reaction.
- There is no clear evidence to suggest that epinephrine is effective in treating all types of hypersensitivity reactions, and its use should be reserved for anaphylaxis or severe allergic reactions 3, 4, 5, 6, 7.
Administration and Dosage of Epinephrine
- Epinephrine should be administered intramuscularly in the lateral thigh, with a dose of 300-600 µg for adults and 10 µg/kg for children 4, 5.
- Epinephrine autoinjectors are available with different doses and needle lengths to accommodate various patient populations, including pediatric and adult patients 5.
- The administration of epinephrine should be repeated every 10-15 minutes if symptoms persist or worsen 4.