What is the immediate treatment for an anaphylactic reaction?

Immediate Treatment for Anaphylactic Reaction

Administer intramuscular epinephrine immediately—this is the only first-line treatment for anaphylaxis and delays in administration are directly associated with fatalities. 1, 2, 3

Primary Treatment: Epinephrine

Epinephrine must be given intramuscularly into the anterolateral thigh (vastus lateralis) at the first recognition of anaphylaxis. 1, 2, 4

Dosing

• Adults and children ≥30 kg: 0.3-0.5 mg of 1:1000 concentration (0.3-0.5 mL) 4
• Children <30 kg: 0.01 mg/kg (maximum 0.3 mg) 1, 2
• Repeat every 5-10 minutes as necessary if symptoms persist or recur 1, 4

Critical Route Considerations

Intramuscular injection in the thigh produces significantly higher peak plasma epinephrine concentrations more rapidly than subcutaneous administration or injection in the arm. 1 The FDA-approved epinephrine formulation has no absolute contraindications for anaphylaxis. 4

Supportive Measures (After Epinephrine)

Fluid Resuscitation

• Administer crystalloid fluid bolus immediately: 0.5-1 L rapid bolus for adults (20 mL/kg for children), repeated as needed for persistent hypotension 1
• Large volumes may be necessary due to vasodilatation and capillary leakage 1

Patient Positioning

• Place patient supine with legs elevated (if tolerated) 1
• In pregnant patients, ensure left uterine displacement to avoid aortocaval compression 1

Adjunct Medications (Second-Line Only)

H1 Antihistamines

Antihistamines should never be used alone or as initial treatment—they only address cutaneous manifestations and have slow onset (30-60 minutes). 2, 3 After adequate epinephrine and stabilization, diphenhydramine 25-50 mg IV/IM may be given. 2, 3

Corticosteroids

Glucocorticoids have no role in acute anaphylaxis due to their 4-6 hour minimum onset of action and do not prevent biphasic reactions. 3 They may be considered only after epinephrine and stabilization in patients with severe/prolonged anaphylaxis, history of idiopathic anaphylaxis, or underlying asthma. 2, 3

Management of Refractory Anaphylaxis

If inadequate response after 10 minutes despite adequate epinephrine and fluids:

• Escalate epinephrine: Double the bolus dose or start epinephrine infusion (0.05-0.1 mcg/kg/min) after three bolus doses 1
• Add alternative vasopressors: Norepinephrine, vasopressin (1-2 IU bolus), phenylephrine, or metaraminol for persistent hypotension 1
• For patients on beta-blockers: Administer IV glucagon 1-2 mg 1, 2
• For persistent bronchospasm: Inhaled bronchodilators (albuterol), consider IV bronchodilators or volatile anesthetics 1

Cardiac Arrest

Follow advanced life support guidelines with IV epinephrine 1 mg boluses. 1 Consider extracorporeal life support if available and skills permit. 1

Post-Resuscitation Monitoring

All patients must be observed in a monitored area for minimum 6 hours from reaction onset due to risk of biphasic reactions (recurrence without re-exposure). 1 Risk factors for biphasic reactions include severe initial anaphylaxis and requirement for multiple epinephrine doses. 1

Mast Cell Tryptase Sampling

• First sample at 1 hour after reaction onset 1
• Second sample at 2-4 hours 1
• Baseline sample ≥24 hours post-reaction for comparison 1

Critical Pitfalls to Avoid

• Never delay epinephrine for antihistamines or corticosteroids—this is the most common fatal error 2, 3, 5
• Never use subcutaneous route—absorption is delayed compared to intramuscular 1
• Never inject into buttocks, digits, hands, or feet—risk of tissue injury 4
• Never administer IV epinephrine outside monitored settings—reserve only for cardiac arrest or profound hypotension unresponsive to IM epinephrine 2, 3
• Never rely on antihistamines alone—they cannot address cardiovascular collapse or respiratory distress 2, 3