What is the immediate treatment for anaphylaxis?

Immediate Treatment for Anaphylaxis

Intramuscular epinephrine is the only first-line treatment for anaphylaxis and must be administered immediately—all other interventions are secondary and should never delay epinephrine. 1, 2

Primary Intervention: Epinephrine Administration

Administer intramuscular epinephrine 0.01 mg/kg (1:1000 concentration) into the vastus lateralis (anterolateral thigh) immediately upon recognition of anaphylaxis. 1, 3

Dosing specifics:

• Adults and children >50 kg: 0.5 mg maximum single dose 1
• Children 25-50 kg: 0.3 mg (or 0.3 mg autoinjector) 1
• Children 10-25 kg: 0.15 mg (or 0.15 mg autoinjector) 1
• Repeat every 5-15 minutes if symptoms persist or progress 1

Critical administration details:

• The lateral thigh (vastus lateralis) is the mandatory injection site because intramuscular administration in the thigh achieves higher peak plasma concentrations more rapidly than subcutaneous or deltoid injection 1
• There are no absolute contraindications to epinephrine in anaphylaxis, including cardiac disease, advanced age, or frailty 1, 2
• Epinephrine autoinjectors should be used if available to minimize dosing errors when staff experience is limited 1

Immediate Concurrent Actions

While preparing or immediately after epinephrine:

• Activate emergency medical services (call 911) 1
• Position patient supine with legs elevated (if tolerated and no respiratory distress) 1
• Administer supplemental oxygen at 6-8 L/min 1, 2
• Establish IV access and give rapid crystalloid bolus: 500-1000 mL in adults, 10-20 mL/kg in children 1, 2

Secondary Adjunctive Treatments (After Epinephrine)

These should never be given before or instead of epinephrine:

For bronchospasm:

• Inhaled albuterol (2.5-5 mg nebulized) for persistent lower respiratory symptoms after epinephrine 1, 2

Antihistamines (limited role):

• H1 antihistamine: Diphenhydramine 25-50 mg IV (1-2 mg/kg in children, max 50 mg) 1
• H2 antihistamine: Ranitidine 50 mg IV over 5 minutes (1 mg/kg in children, diluted in 20 mL) 1, 2
• Note: The combination of H1 + H2 is superior to H1 alone, but these only address cutaneous manifestations and have no role in life-threatening symptoms 1, 2

Glucocorticoids:

• Do NOT administer glucocorticoids for acute anaphylaxis treatment due to slow onset of action (hours) 1, 2
• Do NOT give glucocorticoids to prevent biphasic reactions—multiple systematic reviews show no clear evidence of benefit 1, 2

Repeat Dosing Algorithm

If symptoms persist or progress after initial epinephrine dose:

• Repeat intramuscular epinephrine every 5-15 minutes as needed 1
• Approximately 7-18% of patients require >1 dose of epinephrine 1
• If no response after 2-3 IM doses and patient remains hypotensive, consider IV epinephrine infusion (1:10,000 concentration, NOT 1:1000) in a monitored setting 1, 2

Post-Treatment Observation

All patients must be observed in a monitored setting capable of managing anaphylaxis until symptoms fully resolve: 1

• Minimum 4-6 hours observation for most patients 1, 2
• Extended observation (6-24 hours) or hospital admission for severe reactions requiring >1 dose of epinephrine, as these patients have 4.8-fold increased risk of biphasic anaphylaxis 1
• Biphasic reactions occur in 7-10% of cases, with mean onset at 11 hours (range up to 72 hours) 1

Critical Pitfalls to Avoid

• Delaying epinephrine administration is the leading cause of anaphylaxis fatalities—approximately 500-1000 deaths occur annually in the US, most from delayed epinephrine 1, 2
• Never use antihistamines or glucocorticoids as first-line or sole treatment—this significantly increases mortality risk 1, 2, 4
• Never administer IV epinephrine outside monitored settings or use 1:1000 concentration IV (must use 1:10,000 for IV route) 1, 2
• Do not give epinephrine subcutaneously or in the deltoid—absorption is significantly slower than IM thigh injection 1

Discharge Requirements

Before discharge, ensure patient receives:

• Two epinephrine autoinjectors with proper training 1
• Written anaphylaxis emergency action plan 1
• Referral to allergist for trigger identification and long-term management 1
• Education on biphasic reaction risk and when to use autoinjector 1