What is the appropriate emergency management for a suspected allergic reaction or anaphylaxis, including epinephrine dosing, adjunctive therapies, and follow‑up recommendations?

Emergency Management of Allergic Reactions and Anaphylaxis

Intramuscular epinephrine is the first-line treatment for anaphylaxis and must be administered immediately upon recognition—all other therapies are adjunctive and should never delay epinephrine administration. 1, 2

Immediate Recognition and First-Line Treatment

Epinephrine Dosing (IM Administration)

Administer epinephrine intramuscularly into the anterolateral thigh as soon as anaphylaxis is suspected:

• Adults and children ≥25-30 kg: 0.3-0.5 mg (0.3-0.5 mL of 1:1000 solution) IM 1, 2, 3
• Children <25-30 kg: 0.01 mg/kg IM (maximum 0.3 mg per dose) 1, 2, 3
• Repeat every 5-15 minutes as needed if symptoms persist or progress 1, 3

The anterolateral thigh is the preferred injection site—never inject into buttocks, digits, hands, or feet due to risk of tissue injury 3. Delayed epinephrine administration is directly associated with fatal outcomes; in one study, 6 of 7 children who survived received epinephrine within 30 minutes, while only 2 of 6 who died received it within the first hour 1.

Concurrent Initial Actions

While administering epinephrine, simultaneously:

• Position patient supine with legs elevated (if tolerated and no respiratory distress) 1
• Call for help immediately (activate emergency response/call 911) 1, 2
• Remove allergen exposure if ongoing 1
• Establish large-bore IV access for fluid resuscitation 2, 4

Adjunctive Therapies (After Epinephrine)

Fluid Resuscitation

Aggressive crystalloid administration is critical for hypotension:

• Adults: 1-2 L normal saline rapid IV bolus, repeat as needed 2, 4
• Children: 20 mL/kg normal saline bolus, repeat as needed 1, 2

Large volumes may be required—some patients need several liters due to massive capillary leak 1.

Oxygen and Airway Management

• Supplemental oxygen should be provided to all patients 1
• Assess for laryngeal edema (stridor, voice changes, difficulty swallowing) 2
• Consider early intubation if stridor worsens—waiting may make intubation impossible and require emergency cricothyroidotomy 2

Bronchodilators (for respiratory symptoms)

Albuterol for bronchospasm:

• Children: 4-8 puffs via MDI or 1.5 mL nebulized solution 1
• Adults: 8 puffs via MDI or 3 mL nebulized solution 1
• Repeat every 20 minutes or continuously as needed 1

Antihistamines (Secondary Priority)

H1-antihistamines may be given after adequate epinephrine and fluid resuscitation:

• Diphenhydramine: 1-2 mg/kg IV or oral (maximum 50 mg) 1, 2
• Chlorphenamine: 0.2 mg/kg IV 2

H2-antihistamines:

• Ranitidine: 1 mg/kg IV 2
• Famotidine: 0.25 mg/kg IV 2

Antihistamines have no proven benefit in altering outcomes and should never delay epinephrine 1.

Corticosteroids (Theoretical Benefit Only)

May be administered after adequate resuscitation to potentially prevent biphasic reactions:

• Methylprednisolone: 1-2 mg/kg IV 2
• Hydrocortisone: 5 mg/kg IV 2

Evidence for corticosteroids preventing biphasic reactions is limited, and they have no role in acute symptom management due to delayed onset of action 1.

Refractory Anaphylaxis and IV Epinephrine

When to Consider IV Epinephrine

IV epinephrine should be considered only when:

• Multiple IM doses have failed 4
• Profound hypotension persists despite volume replacement 4
• Patient is in or near cardiac arrest 1, 4

IV Epinephrine Dosing

Bolus dosing (with continuous hemodynamic monitoring):

• Adults: 50-100 mcg IV bolus (0.05-0.1 mg) 2, 4
• Children: 1 mcg/kg IV bolus 2

Continuous infusion (for persistent shock):

• Adults: Start at 1-4 mcg/min (0.05-0.1 mcg/kg/min), titrate up to maximum 10 mcg/min 4
• Children: Start at 0.1 mcg/kg/min, range 0.1-1.0 mcg/kg/min (maximum 5 mcg/kg/min in exceptional circumstances) 4

Preparation: Add 1 mg (1 mL) of 1:1000 epinephrine to 250 mL D5W to yield 4 mcg/mL concentration 4.

Critical warning: IV epinephrine requires continuous blood pressure and cardiac monitoring—never use as first-line therapy 4.

Alternative Vasopressors

For patients on beta-blockers or refractory to epinephrine:

• Glucagon: 1-5 mg IV over 5 minutes (20-30 mcg/kg in children, maximum 1 mg), followed by infusion at 5-15 mcg/min 4
• Norepinephrine infusion: 0.05-0.5 mcg/kg/min if hypotension persists after 10 minutes 5

Diagnostic Testing

Mast Cell Tryptase

Obtain serial tryptase levels to confirm diagnosis:

• First sample: At 1 hour after reaction onset 1
• Second sample: At 2-4 hours after onset 1
• Baseline sample: At least 24 hours post-reaction or at follow-up 1, 2

Without these measurements, anaphylaxis cannot be definitively confirmed or excluded retrospectively 5.

Observation and Disposition

Observation Period

All patients who receive epinephrine must be observed in a monitored setting:

• Minimum observation: 4-6 hours for most patients 1, 2
• Extended observation or ICU admission: For Grade III-IV reactions, prolonged resuscitation, ongoing vasopressor requirements, or severe/refractory symptoms 1

Biphasic reactions occur in 1-20% of cases, typically around 8 hours after initial reaction but can occur up to 72 hours later 1. Risk factors include severe initial reaction and need for multiple epinephrine doses 1.

Discharge Planning and Follow-Up

Every patient discharged after anaphylaxis must receive:

1. Two epinephrine auto-injectors with prescriptions 1, 2
2. Written anaphylaxis emergency action plan 1, 2
3. Education on auto-injector use and when to administer 1, 2
4. Plan for monitoring auto-injector expiration dates 1
5. Referral to allergist/immunologist for comprehensive evaluation and allergy testing 2
6. Medical alert bracelet recommendation 2

High-Risk Populations Requiring Auto-Injectors

Prescribe epinephrine auto-injectors for:

• Previous systemic allergic reaction or anaphylaxis 1
• Food allergy with asthma 1
• Known allergy to peanuts, tree nuts, fish, or crustacean shellfish 1
• Consider for all patients with IgE-mediated food allergies 1

Special Populations and Considerations

Pregnancy

• Management follows same principles as non-pregnant patients 1
• Position with left uterine displacement to avoid aortocaval compression 1
• Early IV epinephrine recommended for Grade III-IV reactions 1
• Consider emergent Caesarean section if persistent hypotension despite resuscitation 1
• Perimortem Caesarean delivery if persistent hypotension after 4 minutes of cardiac arrest 1

Patients on Beta-Blockers

• May have refractory bronchospasm and hypotension 4
• Higher doses of epinephrine may be required 4
• Consider glucagon early (1-5 mg IV over 5 minutes) 4

Mastocytosis

• Increased risk of perioperative anaphylaxis from non-specific triggers 1
• Avoid histamine-releasing agents (atracurium, mivacurium) when possible 1
• Preoperative H1/H2 antagonists and corticosteroids are commonly recommended but lack controlled trial evidence 1

Critical Pitfalls to Avoid

• Never delay epinephrine while giving antihistamines or corticosteroids—these are adjunctive only 1
• Never use IV epinephrine as first-line—always attempt IM dosing first unless in cardiac arrest 4
• Never inject epinephrine into buttocks or extremities—anterolateral thigh only 3
• Never discharge patients without observation period—biphasic reactions can be fatal 1
• Never discharge without prescribing two auto-injectors and providing education 1, 2
• Do not assume isolated hypotension is anaphylaxis—anaphylaxis typically presents with cutaneous (72%), respiratory (40%), or other multi-system findings 5