Treatment of Allergic Reactions
Intramuscular epinephrine is the only first-line treatment for anaphylaxis and must be administered immediately—antihistamines and corticosteroids are adjunctive therapies only and should never replace or delay epinephrine. 1, 2
Immediate Management Algorithm
First-Line Treatment: Epinephrine (IM)
Epinephrine must be given first for any signs of anaphylaxis (multi-system involvement, respiratory symptoms, hypotension, or severe single-organ symptoms). 1
Dosing:
- Adults and children ≥25 kg: 0.3 mg (0.3 mL of 1:1,000 solution) IM into anterolateral thigh 1
- Children 10-25 kg: 0.15 mg IM into anterolateral thigh 1
- Alternative dosing: 0.01 mg/kg per dose, maximum 0.5 mg per dose 1
- Repeat every 5-15 minutes as needed if symptoms persist or progress 1, 2
Critical actions concurrent with epinephrine:
- Call for help (911 in community, resuscitation team in hospital) 1
- Remove allergen exposure 1
- Place patient recumbent with legs elevated (if tolerated) 1
- Administer supplemental oxygen 1
Adjunctive Treatments (Only After Epinephrine)
The most common error is using antihistamines instead of epinephrine, which significantly increases risk of life-threatening progression. 1, 3
H1 Antihistamines:
- Diphenhydramine: 1-2 mg/kg per dose, maximum 50 mg IV or oral (liquid absorbed faster than tablets) 1, 3
- Alternative: non-sedating second-generation antihistamine 1
H2 Antihistamines:
- Ranitidine: 1-2 mg/kg per dose, maximum 75-150 mg oral or IV 1, 3
- H1 and H2 combination works better than either alone 3
Corticosteroids:
- Prednisone: 1 mg/kg, maximum 60-80 mg oral 1, 3
- Methylprednisolone: 1 mg/kg, maximum 60-80 mg IV 1
- Purpose: prevent biphasic or protracted reactions (though evidence is limited) 3
Bronchodilators (if bronchospasm present):
- Albuterol MDI: 4-8 puffs (child) or 8 puffs (adult) 1
- Albuterol nebulized: 1.5 mL (child) or 3 mL (adult) every 20 minutes or continuously 1
IV Fluids:
- Large volumes for orthostasis, hypotension, or incomplete response to epinephrine 1
Refractory Anaphylaxis
For patients not responding to repeated epinephrine:
- Consider continuous epinephrine infusion with hemodynamic monitoring 1
- Glucagon (especially for patients on beta-blockers): 20-30 μg/kg (child) or 1-5 mg (adult), may repeat or follow with infusion of 5-15 μg/min 1, 3
- Vasopressors other than epinephrine, titrated to effect 1
- Atropine for bradycardia, titrated to effect 1
Observation Period
All patients require observation for 4-6 hours minimum, longer based on severity. 1 Patients with severe reactions, delayed initial response, or risk factors (asthma, previous biphasic reactions, remote location from medical care) may need observation up to 12 hours. 4
Discharge Management
Continue adjunctive medications for 2-3 days:
Mandatory discharge requirements:
- Prescribe epinephrine auto-injector (two doses) with hands-on training 1, 3
- Provide written anaphylaxis emergency action plan 1, 3
- Education on allergen avoidance and early symptom recognition 1, 3
- Medical identification jewelry or wallet card 1
- Follow-up with primary care physician and allergist referral 1, 3
Mild Allergic Reactions (No Anaphylaxis)
For isolated skin symptoms (urticaria, localized swelling) without systemic involvement:
- H1 antihistamines are appropriate first-line treatment 1, 5
- Monitor closely for progression to anaphylaxis 5, 4
- Epinephrine should be immediately available 5
Critical Pitfalls to Avoid
- Never delay epinephrine to give antihistamines—this is the most common and dangerous error 1, 3
- Never inject epinephrine into buttocks, digits, hands, or feet—only anterolateral thigh 2
- Do not rely on serum tryptase for acute diagnosis—treatment must be based on clinical presentation 1, 4
- Patients on beta-blockers may not respond to epinephrine—have glucagon ready 1, 3
- Patients with asthma are at higher risk for severe reactions and respiratory compromise 1