What is the management for a suspected type 1 hypersensitivity reaction?

Management of Suspected Type 1 Hypersensitivity Reaction

Administer intramuscular epinephrine immediately as the first and only first-line treatment—this must never be delayed or replaced by antihistamines or corticosteroids. 1, 2, 3

Immediate Treatment Protocol

Primary Intervention

• Epinephrine 0.01 mg/kg intramuscularly (1:1000 concentration) into the vastus lateralis (anterolateral thigh) 1, 2, 3
  • Maximum dose: 0.5 mg in adults, 0.3 mg in children/teenagers 2
  • Repeat every 5-15 minutes if symptoms persist or progress 2
  • No absolute contraindications exist for epinephrine in anaphylaxis 2
  • Delay in epinephrine administration is directly associated with increased mortality and biphasic reactions 1, 2

Secondary Stabilization Measures (After Epinephrine)

• Establish IV access and administer rapid crystalloid bolus 2
  • Adults: 500-1000 mL normal saline or balanced salt solution 2
  • Pediatric patients: 10-20 mL/kg bolus 2
• Supplemental oxygen at 6-8 L/min 2
• Continuous vital sign monitoring 2

Adjunctive Treatments (Only After Epinephrine and Stabilization)

For Respiratory Symptoms

• Inhaled beta-2 agonists (albuterol) for lower respiratory symptoms 2
• Consider IV bronchodilators (ketamine, salbutamol) if bronchospasm persists after 10 minutes 2

Antihistamine Use (Limited Role)

• H1 antihistamines (diphenhydramine 25-50 mg IV slowly) address only cutaneous manifestations (urticaria, pruritus, flushing) 1, 2
• These have slow onset (30 minutes to start, 60-120 minutes to peak) and lack vasoconstrictive, bronchodilatory, or mast cell stabilization properties 1
• H1 + H2 antagonist combination (diphenhydramine + ranitidine 50 mg IV over 5 minutes) is superior to either alone for cutaneous symptoms 2
• H2 antihistamines have no high-quality evidence supporting their use in anaphylaxis and play only a minor role 1

Corticosteroids (Not Recommended for Acute Treatment)

• Glucocorticoids have no proven role in acute anaphylaxis treatment due to slow onset of action (4-6 hours minimum) 1, 2
• The 2020 Anaphylaxis Practice Parameter specifically recommends against routine use to prevent biphasic reactions 1, 2
• Glucocorticoids should never delay or replace epinephrine 2
• May be considered only as adjunctive therapy after epinephrine and stabilization in patients with severe/prolonged anaphylaxis, history of idiopathic anaphylaxis, or underlying asthma 1

Severity-Based IV Epinephrine Dosing (If IV Access Present)

• Grade II (Moderate) anaphylaxis: IV epinephrine 20 mcg (0.02 mg) with 500 mL crystalloid bolus 2
• Grade III (Severe) anaphylaxis: IV epinephrine 50-100 mcg (0.05-0.1 mg) with 1 L crystalloid bolus 2
• Critical warning: Use 1:10,000 concentration for IV administration, NOT 1:1000 2

Post-Stabilization Management

• Minimum 6 hours observation in a monitored setting after symptom resolution 2
• Extend observation to 24 hours for severe reactions or those requiring >1 dose of epinephrine 2

Critical Pitfalls to Avoid

• Never use antihistamines or corticosteroids as first-line treatment instead of epinephrine—this dangerous practice leads to delayed treatment of life-threatening symptoms 1, 2
• Never administer IV epinephrine outside monitored settings or without proper dilution 2
• First-generation H1 antihistamines cause sedation that can decrease awareness of worsening anaphylaxis symptoms 1
• Relying on antihistamines alone cannot address cardiovascular collapse or respiratory distress 1

Context for Type 1 Hypersensitivity

Type 1 hypersensitivity reactions are IgE-mediated immediate reactions that can present with flushing, urticaria, angioedema, bronchospasm, laryngospasm, hypotension, tachycardia, gastrointestinal symptoms, and cardiovascular collapse 3, 4, 5. The key distinguishing feature requiring immediate epinephrine is the presence of respiratory compromise, cardiovascular symptoms, or multi-system involvement beyond isolated cutaneous manifestations 3.