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
First-Line Treatment: Epinephrine
Administer intramuscular epinephrine immediately into the anterolateral thigh (vastus lateralis muscle) using the following dosing:
- Adults and children >25-30 kg: 0.3 mg (using autoinjector or 0.3 mL of 1:1000 solution) 1
- Children 10-25 kg: 0.15 mg (using autoinjector or 0.15 mL of 1:1000 solution) 1
- Weight-based dosing: 0.01 mg/kg intramuscularly (maximum 0.5 mg in adults, 0.3 mg in children) 1, 2, 3
Repeat epinephrine every 5-15 minutes if symptoms persist or progress—approximately 7-18% of patients require more than one dose. 1 There are no absolute contraindications to epinephrine in anaphylaxis, including in patients with cardiac disease, advanced age, or other comorbidities. 1
Critical Pitfall
Delayed epinephrine administration is directly associated with increased mortality and biphasic reactions. 1, 2 Never substitute or delay epinephrine for antihistamines, corticosteroids, or other medications—this significantly increases risk of death. 2, 4
Immediate Secondary Actions (After Epinephrine)
Once epinephrine is administered, simultaneously implement these interventions:
- Position patient supine with legs elevated (or in position of comfort if respiratory distress present) 1
- Activate emergency medical services immediately 1
- Establish IV access and administer rapid fluid bolus: 500-1000 mL crystalloid (normal saline) in adults; 10-20 mL/kg in children 1, 2
- Administer supplemental oxygen at 6-8 L/min 2
Adjunctive Treatments (Never First-Line)
After epinephrine and initial stabilization, consider:
- H1 antihistamine: Diphenhydramine 25-50 mg IV (1-2 mg/kg in children, max 50 mg) 1, 2
- H2 antihistamine: Ranitidine 50 mg IV over 5 minutes (1 mg/kg in children)—the combination of H1 + H2 is superior to H1 alone 1, 2
- Inhaled beta-2 agonist: Albuterol 2.5-5 mg nebulized for persistent bronchospasm despite epinephrine 1, 2
Important caveat: Antihistamines only address cutaneous manifestations (which are not life-threatening) and have much slower onset than epinephrine—they provide no benefit for airway or cardiovascular compromise. 1
Refractory Anaphylaxis
If hypotension persists after 2-3 doses of intramuscular epinephrine and aggressive fluid resuscitation:
- Consider IV epinephrine infusion (1:10,000 concentration, NOT 1:1000) with continuous hemodynamic monitoring 1, 2
- Administer vasopressor infusion (dopamine 2-20 mcg/kg/min) if hypotension is refractory 1
- For patients on beta-blockers: Consider glucagon 1-5 mg IV over 5 minutes, followed by infusion (5-15 mcg/min) 1
What NOT to Do
Do not administer glucocorticoids for acute anaphylaxis—they have no role in immediate treatment due to slow onset of action (hours) and do not prevent biphasic reactions. 1, 2 Multiple systematic reviews confirm glucocorticoids provide no benefit in preventing biphasic anaphylaxis. 1
Do not use IV epinephrine outside monitored settings or without proper dilution (must use 1:10,000 for IV, not 1:1000). 2
Observation Period
Observe all patients for minimum 4-6 hours after complete symptom resolution in a setting capable of managing recurrent anaphylaxis. 1 Extend observation to 6-24 hours for:
- Severe initial reactions 1, 2
- Patients requiring >1 dose of epinephrine (odds ratio 4.82 for biphasic reaction) 1
- History of biphasic reactions 1
Biphasic anaphylaxis occurs in 7-18% of cases, with mean onset at 11 hours (range up to 72 hours). 1
Discharge Requirements
Before discharge, ensure patient receives: