What is the appropriate treatment for an allergic reaction, including anaphylaxis?

Treatment of Allergic Reactions and Anaphylaxis

Intramuscular epinephrine is the only first-line treatment for anaphylaxis and must be administered immediately—there is no substitute. 1, 2, 3

Immediate Management Algorithm

First-Line Treatment: Epinephrine

Epinephrine must be given first before any other medications in suspected anaphylaxis. 1, 2, 4

Dosing for Anaphylaxis:

• Adults and children ≥30 kg: 0.3-0.5 mg (0.3-0.5 mL of 1 mg/mL solution) intramuscularly 3
• Children <30 kg: 0.01 mg/kg (up to 0.3 mg maximum) intramuscularly 3
• Route: Inject into the anterolateral thigh (vastus lateralis muscle) 3
• Repeat dosing: Every 5-10 minutes as necessary if symptoms persist 3, 5

Critical warning: Never inject into buttocks, digits, hands, or feet due to risk of tissue necrosis. 3

When to Administer Epinephrine:

Give epinephrine immediately if the patient has any of the following after allergen exposure: 1

• Diffuse hives or urticaria
• Shortness of breath or any respiratory symptoms
• Obstructive swelling of tongue/lips interfering with breathing
• Circulatory symptoms (hypotension, syncope, pallor)
• Wheezing or bronchospasm
• Throat tightness or sensation of throat closing 1

Supportive Care (Concurrent with Epinephrine)

• Activate emergency medical services immediately 1
• Position patient supine with legs elevated (unless respiratory distress requires upright position) 1
• Remove allergen/trigger if still present 5
• Administer supplemental oxygen if available 1
• Establish IV access for fluid resuscitation 1

Refractory Anaphylaxis

For patients not responding to initial epinephrine: 1

• Crystalloid fluids: 20 mL/kg bolus, repeat as needed 1
• Second epinephrine dose: If no response after 5-10 minutes 1, 3
• Alternative vasopressors for persistent hypotension: vasopressin, norepinephrine, metaraminol, or phenylephrine 1
• Glucagon: 20-30 μg/kg (children) or 1-5 mg (adults) for patients on beta-blockers who may have reduced epinephrine response 2

Second-Line Adjunctive Treatments

These medications should ONLY be given AFTER epinephrine administration—never delay epinephrine to give these drugs. 2

H1 Antihistamines

• Diphenhydramine: 1-2 mg/kg per dose (maximum 50 mg) IV or oral 2
• Continue every 6 hours for 2-3 days after discharge 2
• Purpose: Relieves itching and urticaria, but has much slower onset than epinephrine 2

H2 Antihistamines

• Ranitidine or famotidine: 1-2 mg/kg per dose (maximum 75-150 mg) oral or IV 2
• Combination therapy: H1 + H2 antihistamines work better than either alone 2

Corticosteroids

• Prednisone: 1 mg/kg (maximum 60-80 mg) orally 2
• Purpose: May prevent biphasic or protracted reactions, though evidence is limited 1, 2
• Give after adequate resuscitation is established 1

Bronchodilators

• Inhaled beta-agonists (albuterol) for persistent bronchospasm 1
• Consider IV bronchodilators if inhaled therapy insufficient 1

Observation Period

• Minimum observation: 4-6 hours from reaction onset for all patients 1, 5
• Extended observation (up to 12 hours) for: 5
  • Severe initial presentation
  • History of biphasic reactions
  • Delayed epinephrine administration
  • Ongoing symptoms requiring multiple epinephrine doses

Important: Biphasic reactions (recurrence without re-exposure) occur in 7-18% of cases and can happen outside typical observation windows. 1, 5

High-Risk Populations Requiring Extra Caution

Patients on Beta-Blockers

• At increased risk for severe, refractory anaphylaxis 1
• May require higher epinephrine doses or alternative vasopressors 1
• Have glucagon immediately available 2

Patients with Asthma

• Particularly those with poorly controlled asthma are at higher risk for severe reactions and fatal outcomes 1
• Assess asthma control before any planned allergen exposure (e.g., immunotherapy) 1

Patients with Cardiovascular Disease

• Epinephrine may aggravate angina or produce arrhythmias 3
• However, do not withhold epinephrine—it remains life-saving and benefits outweigh risks 3

Common Pitfalls to Avoid

1. Using antihistamines as primary treatment: This is the most common error and significantly increases risk of progression to life-threatening reactions 2

2. Delaying epinephrine administration: Waiting to "see if symptoms worsen" increases mortality—give epinephrine at first suspicion of anaphylaxis 4, 5

3. Inadequate observation time: Discharging patients too early may miss biphasic reactions 5

4. Wrong injection site: Subcutaneous or IV bolus (outside of shock) has slower/less predictable absorption than IM thigh injection 3

5. Failing to prescribe epinephrine auto-injectors: All patients who experience anaphylaxis must be discharged with two epinephrine auto-injectors and proper training 1, 2

Discharge Planning

Before discharge, ensure: 1, 2

• Two epinephrine auto-injectors prescribed with demonstration of proper use
• Written anaphylaxis emergency action plan provided
• Allergen avoidance education completed
• Referral to allergist arranged
• Medical alert identification recommended
• Follow-up appointment scheduled with primary care physician

Mild Allergic Reactions (Non-Anaphylactic)

For isolated mild symptoms (few hives, mild itching) without systemic involvement: 1

• Oral antihistamines are appropriate first-line treatment
• Still prescribe epinephrine auto-injector as reactions can progress unpredictably
• Educate on warning signs requiring epinephrine use

The presence of sulfites in epinephrine formulations should never deter its use in anaphylaxis. 3