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

Treatment of Allergic Reactions Including Anaphylaxis

Epinephrine is the first-line treatment for anaphylaxis and should be administered promptly via intramuscular injection into the anterolateral thigh for all patients experiencing anaphylactic reactions. 1, 2

Initial Assessment and Management

• Allergic reactions exist on a spectrum from mild, localized symptoms to life-threatening anaphylaxis with multisystem involvement 3
• Signs and symptoms of anaphylaxis include:
  • Skin: urticaria, angioedema, flushing, pruritus
  • Respiratory: difficulty breathing, bronchospasm, laryngospasm, airway swelling
  • Cardiovascular: hypotension, tachycardia, syncope
  • Gastrointestinal: vomiting, diarrhea, abdominal cramps 2

Treatment Algorithm

For Anaphylaxis (Severe Systemic Reaction):

1. Administer epinephrine immediately:

   • Adults and children ≥30 kg: 0.3-0.5 mg (0.3-0.5 mL) IM into anterolateral thigh 2
   • Children <30 kg: 0.01 mg/kg (0.01 mL/kg) up to 0.3 mg IM into anterolateral thigh 2
   • May repeat every 5-10 minutes as necessary if symptoms persist 2

2. Activate emergency response system 1

3. Position patient appropriately:

   • Supine position with legs elevated for hypotension
   • Semi-recumbent position for respiratory distress
   • Pregnant patients should have left uterine displacement 1

4. Administer second-line medications (after epinephrine):

   • H1 antihistamines: Diphenhydramine 1-2 mg/kg (max 50 mg) IV or oral 4
   • H2 antihistamines: Ranitidine 1-2 mg/kg (max 75-150 mg) IV or oral 4
   • Corticosteroids: Prednisone 1 mg/kg (max 60-80 mg) orally 4

5. Consider additional interventions:

   • Oxygen supplementation for hypoxemia 1
   • IV fluid resuscitation for hypotension (crystalloids) 1
   • For patients on beta-blockers with refractory hypotension: Glucagon 20-30 μg/kg for children or 1-5 mg for adults 4

6. Monitor for biphasic reactions:

   • Observe for at least 4-12 hours depending on severity and risk factors 5
   • Consider repeat dose of epinephrine if symptoms recur or don't respond to initial dose 1

For Mild-Moderate Allergic Reactions (Without Systemic Involvement):

• H1 antihistamines for symptom relief 1
• Local treatments for cutaneous symptoms (cool compresses, topical corticosteroids) 1
• Monitor for progression to anaphylaxis 1

Special Considerations

• Asthma patients: Higher risk for severe anaphylaxis; ensure asthma is well-controlled 1
• Patients on beta-blockers: May have reduced response to epinephrine; consider glucagon for refractory hypotension 4
• Pregnancy: Position with left uterine displacement; treatment principles remain the same 1
• Delayed reactions: Can occur after 30 minutes; patients should be counseled on this possibility 1

Post-Reaction Care

• Prescribe epinephrine auto-injector (2 doses) for patients at risk of recurrent anaphylaxis 4
• Provide education on proper use of auto-injector 4
• Refer to allergist for identification of triggers and long-term management 5
• Develop an emergency action plan 4
• Continue H1 antihistamines every 6 hours for 2-3 days after discharge 4

Common Pitfalls to Avoid

• Delaying epinephrine administration: This is the most common error in anaphylaxis management and increases mortality risk 6
• Using antihistamines as first-line treatment: Antihistamines should never replace epinephrine for anaphylaxis 4
• Improper injection site: Do not inject epinephrine into buttocks, digits, hands, or feet 2
• Withholding epinephrine due to fear of side effects: When given properly as IM injection, the risk of serious side effects is low 7
• Failing to observe patients adequately: Biphasic reactions can occur hours after initial symptoms resolve 5

By following this treatment algorithm, clinicians can effectively manage allergic reactions and anaphylaxis, minimizing morbidity and mortality through prompt recognition and appropriate intervention.