What is the treatment for anaphylaxis in adults and children with a history of allergies?

Treatment of Anaphylaxis in Adults and Children

Immediate intramuscular epinephrine injected into the anterolateral thigh is the first and only appropriate first-line treatment for anaphylaxis in both adults and children, and must be administered at the first sign of anaphylactic reaction. 1, 2, 3

Immediate First-Line Treatment: Epinephrine

Epinephrine is the only medication that prevents and reverses upper and lower airway obstruction and cardiovascular collapse—there are no absolute contraindications to its use in anaphylaxis. 2, 3, 4

Dosing and Administration

Adults and children ≥25-30 kg:

• Administer 0.3-0.5 mg of 1:1000 epinephrine (0.3-0.5 mL) intramuscularly into the anterolateral aspect of the mid-thigh 1, 3, 4
• Use 0.30 mg autoinjector for individuals weighing approximately 25 kg or more 2

Children 10-25 kg:

• Administer 0.01 mg/kg intramuscularly, up to maximum 0.3 mg 1, 4
• Use 0.15 mg autoinjector for children in this weight range 1, 2

Infants <10 kg:

• Use 0.1 mg autoinjector where available; if unavailable, 0.15 mg dose is appropriate for infants >7.5 kg 2

Route Matters Critically

The intramuscular route in the lateral thigh (vastus lateralis) achieves faster and higher plasma epinephrine levels compared to subcutaneous or deltoid injection. 2 Never inject into buttocks, digits, hands, or feet due to risk of tissue necrosis 4. The subcutaneous route delays onset of action, and intravenous administration in non-arrest situations increases risk of cardiac adverse effects 3, 5.

Repeat Dosing

Epinephrine can and should be repeated every 5-15 minutes if symptoms persist or do not respond adequately. 1, 3, 4 Between 7-18% of patients require more than one dose 1. If EMS arrival will exceed 5-10 minutes and the patient has not responded to initial epinephrine, administer a repeat dose 1.

Concurrent Supportive Measures

Position the patient supine with legs elevated (unless respiratory distress prevents this positioning) 2. In pregnant women, perform left uterine displacement to avoid aortocaval compression 2. Activate emergency medical services immediately—anaphylaxis can require advanced interventions including intubation, IV vasopressors, and intensive care 1, 3.

Establish IV access and administer supplemental oxygen. 2, 3

Fluid Resuscitation

For hypotension or shock, aggressive fluid resuscitation is imperative to combat vasodilation and capillary leak 2, 3:

• Grade II reactions: Initial bolus of 0.5 L crystalloids 2
• Grade III reactions: Initial bolus of 1 L crystalloids 2
• Repeat boluses as needed, up to 20-30 mL/kg based on clinical response 2

Second-Line Adjunctive Therapies (Never Replace Epinephrine)

Antihistamines and corticosteroids are adjunctive only and should never delay or substitute for epinephrine. 2, 3 They do not prevent or reverse airway obstruction or cardiovascular collapse 2.

After adequate epinephrine administration, consider:

• H1 antihistamines: Diphenhydramine 25-50 mg IV (or 1-2 mg/kg in children, max 50 mg) 2, 3
• H2 antihistamines: Ranitidine 50 mg IV in adults (1 mg/kg in children) may be superior when combined with H1 blockers 3
• Bronchodilators: For persistent bronchospasm despite adequate epinephrine, nebulized albuterol 2.5-5 mg 3

Management of Refractory Anaphylaxis

If hypotension persists after initial IM epinephrine and fluid resuscitation:

• Consider IV epinephrine boluses: 20 μg for Grade II reactions, 50-100 μg for Grade III reactions 2
• For continued refractory symptoms after more than three epinephrine boluses, initiate epinephrine infusion at 0.05-0.1 μg/kg/min 2, 3
• Alternative vasopressors (norepinephrine, vasopressin, dopamine) may be used for persistent hypotension 2, 3

Special consideration for patients on beta-blockers: These patients may not respond to epinephrine and require glucagon 1-2 mg IV (or 1-5 mg over 5 minutes, followed by infusion of 5-15 μg/min) 2, 3.

Observation Period

All patients must be observed for a minimum of 6 hours in a monitored area or until stable and symptoms have completely resolved 2, 3. Patients with Grade III-IV reactions typically require ICU admission 2. High-risk patients (severe anaphylaxis, required multiple epinephrine doses) may need extended observation beyond 6 hours due to risk of biphasic reactions 2.

Discharge Requirements

Every patient who experienced anaphylaxis must be discharged with:

• Two epinephrine autoinjectors (0.15 mg for 10-25 kg; 0.3 mg for ≥25 kg) 2
• Written, personalized anaphylaxis emergency action plan detailing symptoms, triggers, and clear instructions 2
• Referral to allergist for trigger identification and ongoing risk assessment 2, 3
• Education emphasizing that delayed epinephrine administration is directly associated with anaphylaxis fatalities—inject at the earliest sign of reaction 2

Patients must understand to always seek emergency care after using epinephrine, even if symptoms improve, due to risk of biphasic reactions hours later 2.

Critical Pitfalls to Avoid

• Never use antihistamines or corticosteroids as first-line treatment instead of epinephrine 3—this is the most common fatal error
• Never delay epinephrine while waiting to "see if symptoms worsen"—immediate administration saves lives 2, 5
• Never discharge patients without two autoinjectors and written action plan 2
• Never administer epinephrine subcutaneously or into the deltoid—these routes are inferior 2
• Do not discharge patients prematurely without adequate observation for biphasic reactions 3