What is the initial treatment for an allergic reaction?

Initial Treatment for Allergic Reactions

Intramuscular epinephrine is the first-line treatment for anaphylaxis and severe allergic reactions and must be administered immediately—all other medications are adjunctive and should never replace or delay epinephrine. 1, 2, 3

Immediate Management Algorithm

Step 1: Recognize and Act

• Administer epinephrine IM immediately into the anterolateral thigh at the first sign of anaphylaxis (systemic symptoms involving skin, respiratory, cardiovascular, or gastrointestinal systems) 1, 2
• Do not delay epinephrine to give antihistamines—this is the most common error and significantly increases risk of progression to life-threatening reactions 1, 4
• Call for help (911 in community settings, resuscitation team in hospitals) while administering epinephrine 1

Step 2: Epinephrine Dosing

Adults and children ≥30 kg:

• 0.3-0.5 mg (0.3-0.5 mL of 1:1,000 solution) IM into anterolateral thigh 3

Children <30 kg:

• 0.01 mg/kg (maximum 0.3 mg) IM into anterolateral thigh 2, 3

Repeat dosing:

• Repeat every 5-15 minutes as needed if symptoms persist or progress 2, 3
• Epinephrine remains first-line therapy over adjunctive treatments even when response is suboptimal 1

Step 3: Concurrent Supportive Measures

• Position patient recumbent with lower extremities elevated (if tolerated) 1
• Provide supplemental oxygen for any respiratory distress 2
• Establish IV access and administer fluid boluses (10-20 mL/kg, repeated as needed) for hypotension or incomplete response to epinephrine 2

Step 4: Adjunctive Medications (After Epinephrine)

These are secondary treatments only and should never replace epinephrine 1:

H1 antihistamines:

• Diphenhydramine 1-2 mg/kg (maximum 50 mg) IV or oral 4, 2
• Continue every 6 hours for 2-3 days after discharge 4

H2 antihistamines:

• Ranitidine 1-2 mg/kg (maximum 75-150 mg) or famotidine IV/oral 4
• Combination of H1 and H2 antihistamines is more effective than either alone 4

Bronchodilators (if wheezing persists):

• Albuterol 4-8 puffs (child) or 8 puffs (adult) via MDI, or nebulized every 20 minutes 2

Corticosteroids:

• Prednisone 1 mg/kg (maximum 60-80 mg) oral or methylprednisolone IV 4
• May help prevent biphasic reactions, though evidence is limited 4

Critical Pitfalls to Avoid

Common Error #1: Using Antihistamines Instead of Epinephrine

• Using antihistamines as primary treatment is the most frequently reported reason for not using epinephrine and places patients at significantly increased risk 1, 4
• Antihistamines have much slower onset of action than epinephrine and cannot prevent progression to life-threatening reactions 4

Common Error #2: Wrong Route or Site

• Never inject into buttocks, digits, hands, or feet 3
• Intramuscular injection into the anterolateral thigh provides optimal absorption 2, 3
• Subcutaneous administration is acceptable but less preferred than IM 3

Common Error #3: Withholding Epinephrine Due to Cardiovascular Concerns

• There are no absolute contraindications to epinephrine in anaphylaxis 1
• The risk of death from anaphylaxis outweighs concerns about cardiovascular effects 1
• Serious adverse effects from properly administered epinephrine are rare in otherwise healthy individuals 2

Special Populations

Patients on beta-blockers:

• May have reduced response to epinephrine 4, 2
• Have glucagon available: 20-30 μg/kg (children) or 1-5 mg (adults) for refractory hypotension 4, 2
• Still administer epinephrine as first-line treatment 2

Patients with cardiovascular disease:

• Epinephrine is still indicated—serious adverse effects are rare 2
• Monitor closely but do not withhold treatment 1

Observation and Disposition

Minimum observation period:

• All patients receiving epinephrine must be observed for 4-6 hours minimum 2

Extended observation (12 hours) required for:

• Severe initial reactions 2
• History of biphasic reactions 2
• Delayed epinephrine administration 2
• Ongoing symptoms despite treatment 2

Discharge Planning

Prescribe at discharge:

• Two epinephrine auto-injectors with hands-on training 4, 2
• Written anaphylaxis emergency action plan 4, 2
• Continue adjunctive medications (antihistamines) for 2-3 days 4

Follow-up:

• Arrange appointment with primary care physician and allergist/immunologist 4, 2
• Provide education on allergen avoidance 4
• Consider medical identification jewelry or wallet card 2

Mild Allergic Reactions (Without Anaphylaxis)

For localized reactions without systemic symptoms:

• H1 antihistamines (oral diphenhydramine or cetirizine) are appropriate 1
• Local treatment with cool compresses or topical corticosteroids 1
• However, if any doubt exists about progression to anaphylaxis, err on the side of caution and administer epinephrine 5