What is the recommended treatment for an allergic reaction?

Treatment for Allergic Reactions

Intramuscular epinephrine is the first-line treatment for anaphylaxis and severe allergic reactions, administered immediately at 0.01 mg/kg (maximum 0.5 mg) into the anterolateral thigh, with doses repeated every 5-15 minutes as needed. 1, 2

Severity-Based Treatment Algorithm

Severe Reactions (Anaphylaxis)

Anaphylaxis presents with respiratory compromise (bronchospasm, laryngeal edema), cardiovascular collapse (hypotension, syncope), or multi-system involvement (skin + respiratory or cardiovascular symptoms). 1, 3

Immediate First-Line Treatment:

• Epinephrine IM: 0.01 mg/kg per dose into the anterolateral thigh 1, 2
  • Children ≤25 kg: 0.15 mg (epinephrine auto-injector) 1
  • Children >25 kg and adults: 0.3-0.5 mg 1, 2
  • Repeat every 5-15 minutes as necessary 1
• Position patient recumbent with lower extremities elevated if tolerated 1
• Call emergency services and transfer to emergency facility 1

Critical Pitfall: Using antihistamines instead of epinephrine is the most common reason for not administering epinephrine and significantly increases risk of life-threatening progression. 1 There are no absolute contraindications to epinephrine in anaphylaxis—the risk of death from untreated anaphylaxis outweighs all other concerns. 1

Adjunctive Treatments (only after epinephrine):

• Supplemental oxygen 1
• IV fluids: Large volumes (10-20 mL/kg bolus) for orthostasis, hypotension, or incomplete response to epinephrine 1
• Albuterol for bronchospasm: 4-8 puffs (child) or 8 puffs (adult) via MDI, or nebulized solution every 20 minutes 1
• H1 antihistamine (diphenhydramine): 1-2 mg/kg per dose, maximum 50 mg IV or oral 1
• H2 antihistamine (ranitidine): 1-2 mg/kg per dose, maximum 75-150 mg 1
• Corticosteroids: Prednisone 1 mg/kg (maximum 60-80 mg) oral or methylprednisolone 1 mg/kg (maximum 60-80 mg) IV 1

For Refractory Hypotension:

• Glucagon (especially for patients on beta-blockers): Children 20-30 μg/kg, adults 1-5 mg IV, may repeat or follow with infusion of 5-15 μg/min 1
• Vasopressors other than epinephrine, titrated to effect 1
• Atropine for bradycardia 1

Mild to Moderate Reactions

Isolated urticaria, flushing, mild angioedema without respiratory or cardiovascular involvement, or oral allergy syndrome symptoms. 1

Treatment:

• H1 antihistamine: Diphenhydramine 1-2 mg/kg (maximum 50 mg) oral, or second-generation antihistamine (e.g., fexofenadine 180 mg) 1, 4
• H2 antihistamine: Ranitidine may be added 1
• Close observation is mandatory to monitor for progression to anaphylaxis 1
• Administer epinephrine immediately if symptoms progress or worsen 1

Important Caveat: If the patient has a history of prior severe allergic reactions, administer epinephrine promptly even at the onset of mild symptoms rather than waiting for progression. 1

Hospital-Based Management

In addition to outpatient measures:

• Consider continuous epinephrine infusion for persistent hypotension with continuous blood pressure and heart rate monitoring 1
• Alternative routes: endotracheal or intraosseous epinephrine if IV/IM access unavailable 1
• Observation period: 4-6 hours minimum, longer for severe reactions or risk factors for biphasic reactions 1

Discharge Management

All patients treated for anaphylaxis must receive: 1

• Epinephrine auto-injector prescription (2 doses) with hands-on training 1
• Written anaphylaxis emergency action plan 1
• Adjunctive medications for 2-3 days:
  • H1 antihistamine (diphenhydramine every 6 hours or non-sedating alternative) 1
  • H2 antihistamine (ranitidine twice daily) 1
  • Corticosteroid (prednisone daily) 1
• Education on: allergen avoidance, early recognition of anaphylaxis signs, proper epinephrine administration technique 1
• Follow-up with primary care physician and consideration for allergist referral 1
• Medical identification jewelry or anaphylaxis wallet card 1

Key Clinical Pearls

Epinephrine Administration Technique:

• Inject into anterolateral thigh only—never buttocks, digits, hands, or feet 2
• Intramuscular route preferred over subcutaneous for faster absorption 2, 3
• Oral liquid diphenhydramine is more readily absorbed than tablets 1

Monitoring for Biphasic Reactions:

• Biphasic reactions (recurrence without re-exposure) can occur in up to 20% of cases 3
• Higher risk with severe initial reactions, delayed epinephrine administration, or history of biphasic reactions 3
• Observation period should be extended to 12 hours for high-risk patients 3

Special Populations at Higher Risk:

• Patients with asthma, cardiovascular disease, mast cell disorders, or on beta-blockers require heightened vigilance 3
• Patients on beta-blockers may require glucagon for refractory symptoms 1