What is the treatment for an allergic reaction?

Treatment of Allergic Reactions

Intramuscular epinephrine is the first-line treatment for anaphylaxis and should be administered immediately at the onset of symptoms—there are no absolute contraindications to its use in anaphylaxis. 1, 2

Immediate Management Algorithm

Epinephrine Administration (First-Line)

• Adults and children ≥30 kg: 0.3-0.5 mg (0.3-0.5 mL of 1:1,000 solution) intramuscularly into the anterolateral thigh 1, 3
• Children <30 kg: 0.01 mg/kg (maximum 0.3 mg) intramuscularly into the anterolateral thigh 1, 3
• Repeat every 5-15 minutes as necessary if symptoms persist or recur 1, 2
• The anterolateral thigh is the preferred injection site—never inject into buttocks, digits, hands, or feet 3

Patient Positioning

• Place patient in recumbent position with lower extremities elevated if tolerated 1, 2
• In pregnant patients, ensure left uterine displacement to avoid aortocaval compression 1

Adjunctive Treatments (Only After Epinephrine)

Oxygen and IV Fluids:

• Administer supplemental oxygen as needed 1, 2
• Give large-volume IV crystalloid fluids (normal saline preferred) for orthostasis, hypotension, or incomplete response to epinephrine 1, 2

Bronchodilators (for bronchospasm):

• Albuterol via MDI: 4-8 puffs (children) or 8 puffs (adults) 1, 2
• Nebulized solution: 1.5 mL (children) or 3 mL (adults) every 20 minutes or continuously 1, 2

Antihistamines (second-line agents):

• H1 antihistamine: Diphenhydramine 1-2 mg/kg per dose (maximum 50 mg IV or oral; oral liquid absorbed better than tablets) 1, 2
• H2 antihistamine: Ranitidine 1-2 mg/kg per dose (maximum 75-150 mg oral or IV) 1

Corticosteroids (second-line agents):

• Prednisone 1 mg/kg (maximum 60-80 mg) orally OR methylprednisolone 1 mg/kg (maximum 60-80 mg) IV 1

Severity-Based Treatment Approach

Mild Reactions (Isolated Urticaria, Mild Angioedema, Oral Allergy Syndrome)

• H1 and H2 antihistamines may be sufficient 1
• Critical caveat: Maintain ongoing observation—if progression occurs or patient has history of prior severe reaction, administer epinephrine immediately 1

Severe Reactions (Anaphylaxis)

• Epinephrine is mandatory as first-line treatment 1, 2
• For patients with known severe food allergy and asthma, consider giving epinephrine at onset of even mild symptoms 1, 2

Refractory Anaphylaxis Management

For persistent hypotension despite epinephrine:

• Continuous epinephrine infusion with hemodynamic monitoring 1
• Additional vasopressors (other than epinephrine) titrated to effect 1
• Glucagon for patients on beta-blockers: 20-30 μg/kg (children) or 1-5 mg (adults), may repeat or follow with infusion 1
• Prompt ICU transfer is essential 1

Observation Period

• Minimum 4-6 hours observation in a monitored medical facility for all patients receiving epinephrine 1, 2
• Longer observation for severe reactions (Grades III-IV), which typically require ICU admission 1
• Monitor for biphasic reactions (recurrence without re-exposure to allergen) 1, 4

Discharge Management

Prescriptions and Education:

• Provide two epinephrine auto-injectors with demonstration of proper use 1, 2
• Written anaphylaxis emergency action plan 1, 2
• Medical identification jewelry or wallet card 1

Adjunctive medications for 2-3 days:

• H1 antihistamine (diphenhydramine) every 6 hours 1
• H2 antihistamine (ranitidine) twice daily 1
• Corticosteroid (prednisone) daily 1

Follow-up:

• Appointment with primary care physician 1
• Referral to allergist/immunologist for further evaluation 1, 4

Critical Clinical Pearls

High-Risk Populations:

• Adolescents and young adults with known food allergy and prior anaphylaxis 2
• Patients with coexisting asthma (higher risk for severe reactions) 1, 2, 4
• Those with cardiovascular disease, on MAO inhibitors, tricyclic antidepressants, or beta-blockers require careful monitoring but epinephrine should NOT be withheld 1, 2

Common Pitfalls to Avoid:

• Delayed epinephrine administration is the primary factor in anaphylaxis fatalities—do not wait for symptom progression 1, 2, 5
• Antihistamines and bronchodilators alone are insufficient for anaphylaxis treatment 1
• The presence of sulfites in epinephrine formulations should not deter use 3
• Risk of cardiac adverse effects from epinephrine is lower than the risk of death from untreated anaphylaxis 1, 5