What is the classification, indication, route, dosage, contraindications, adverse reactions, interactions, and effects of epinephrine?

Epinephrine: Classification, Indications, and Clinical Applications

Epinephrine is a non-selective alpha and beta adrenergic agonist that serves as the first-line medication for anaphylaxis and cardiac arrest, with specific dosing and administration routes based on the clinical scenario. 1, 2

Classification and Pharmacologic Effects

• Epinephrine is classified as a catecholamine with both alpha and beta adrenergic receptor agonist properties 1
• Alpha-1 adrenergic effects include increased vasoconstriction, increased peripheral vascular resistance, and decreased mucosal edema 1
• Beta-1 adrenergic effects include increased inotropy (contractility) and increased chronotropy (heart rate) 1
• Beta-2 adrenergic effects include bronchodilation and decreased release of inflammatory mediators from mast cells and basophils 1

Primary Indications

• Emergency treatment of allergic reactions (Type 1), including anaphylaxis - first-line therapy 1, 2
• Cardiac arrest - as part of advanced cardiac life support protocols 1, 3
• Severe shock states requiring vasopressor support 1
• Severe asthma exacerbations (though selective beta-2 agonists are typically preferred) 1

Routes and Dosages

For Anaphylaxis:

• Intramuscular (IM) administration is preferred using 1:1000 concentration (1 mg/mL) 1, 4
  • Adults and children ≥30 kg: 0.3-0.5 mg (0.3-0.5 mL) IM into anterolateral thigh every 5-10 minutes as needed 2
  • Children <30 kg: 0.01 mg/kg (0.01 mL/kg), up to 0.3 mg (0.3 mL) IM into anterolateral thigh every 5-10 minutes as needed 2
  • Auto-injector dosing: 0.15 mg for children <25 kg; 0.3 mg for children >25 kg and adults 1

For Cardiac Arrest:

• Intravenous (IV) or intraosseous (IO) administration using 1:10,000 concentration (0.1 mg/mL) 1, 4
  • Adults: 1 mg IV/IO every 3-5 minutes during resuscitation 1
  • Children: 0.01 mg/kg (0.1 mL/kg) of 1:10,000 solution, maximum 1 mg per dose 1, 4

For Shock/Hemodynamic Support:

• Continuous IV infusion 1
  • Low-dose (<0.3 mcg/kg/min): Primarily beta effects (increased heart rate, contractility) 1
  • High-dose (>0.3 mcg/kg/min): Predominantly alpha effects (vasoconstriction) 1
  • Typical range: 0.05-1.0 mcg/kg/min, titrated to effect 1

Contraindications and Precautions

• No absolute contraindications when used for anaphylaxis 5
• Relative precautions (not contraindications) when used for anaphylaxis include: 1, 2
  • Coronary artery disease
  • Cardiac arrhythmias
  • Hypertension
  • Hyperthyroidism
  • Parkinson's disease
  • Diabetes mellitus
  • Pheochromocytoma
• Do not inject into buttocks, digits, hands, or feet due to risk of tissue ischemia 2
• Use with caution in elderly patients and pregnant women 2

Adverse Reactions and Side Effects

Common/Mild:

• Anxiety, restlessness, tremor, dizziness, headache, pallor 1, 2
• Palpitations, tachycardia 1, 2
• Nausea, vomiting 2
• Sweating 2

Severe (rare):

• Ventricular arrhythmias 1, 2
• Angina or myocardial infarction, especially in patients with underlying heart disease 1, 2
• Pulmonary edema 1
• Sudden sharp increase in blood pressure potentially causing cerebral hemorrhage, particularly in elderly patients 1, 2
• Tissue necrosis if injected into digits or extremities 2

Drug Interactions

• Sympathomimetic agents: possible additive effects 2
• Cardiac glycosides, halogenated anesthetics, diuretics: increased risk of cardiac arrhythmias 2
• Tricyclic antidepressants, MAO inhibitors, levothyroxine: potentiate effects of epinephrine 2
• Beta-blockers: antagonize cardiostimulating and bronchodilating effects of epinephrine 2
• Alpha-blockers: antagonize vasoconstricting and hypertensive effects 2
• Ergot alkaloids: may reverse pressor response 2

Assessment Before and After Administration

Before Administration:

• Assess vital signs including blood pressure, heart rate, respiratory rate, and oxygen saturation 1
• Evaluate for signs and symptoms of anaphylaxis or shock 1
• Review patient's medical history for conditions requiring cautious use 2
• Check for potential drug interactions 2

After Administration:

• Monitor vital signs frequently, especially blood pressure and heart rate 1
• Assess for improvement in clinical symptoms (e.g., resolution of urticaria, angioedema, respiratory distress in anaphylaxis) 1
• Evaluate for adverse effects, particularly cardiac arrhythmias 1, 2
• For continuous infusions, titrate dose based on hemodynamic response 1
• Consider chest X-ray to evaluate cardiac and pulmonary status in critically ill patients 1

Hemodynamic and Multi-System Effects

• Cardiovascular: Increased heart rate, contractility, blood pressure, and coronary perfusion 1
• Respiratory: Bronchodilation, decreased mucosal edema 1
• Metabolic: May cause hyperglycemia, especially in diabetic patients 1, 2
• Neurological: Central nervous system stimulation causing anxiety, restlessness 2

Evaluation and Desired Outcomes

• In anaphylaxis: Resolution of respiratory distress, hypotension, and cutaneous symptoms 1
• In cardiac arrest: Return of spontaneous circulation 1, 3
• In shock states: Improved blood pressure, tissue perfusion, and end-organ function 1

Important Clinical Considerations

• Epinephrine has a rapid onset but short duration of action (minutes), often requiring repeated doses 1
• 10-20% of patients with anaphylaxis may require more than one dose of epinephrine 1
• IM injection in the anterolateral thigh is preferred over subcutaneous due to faster absorption 1, 4
• Failure to administer epinephrine early in anaphylaxis has been repeatedly implicated in fatalities 1, 5
• The use of antihistamines instead of epinephrine for anaphylaxis is a common but potentially dangerous practice 1