What is the appropriate emergency department management for a patient presenting with severe pruritus due to a suspected hypersensitivity reaction?

Management of Severe Pruritus from Hypersensitivity in the Emergency Department

For severe pruritus suspected to be from a hypersensitivity reaction in the ER, immediately assess for signs of anaphylaxis (respiratory compromise, hypotension, angioedema) and administer intramuscular epinephrine 0.3-0.5 mg if present, as pruritus alone may represent the initial manifestation of evolving anaphylaxis that can rapidly progress to life-threatening cardiovascular or respiratory collapse. 1, 2

Initial Assessment and Risk Stratification

Rapidly determine if this is isolated pruritus or early anaphylaxis:

• Assess vital signs immediately (blood pressure, heart rate, respiratory rate, oxygen saturation) to identify cardiovascular or respiratory compromise 2
• Examine for urticaria and angioedema, which occur in approximately 75% of anaphylaxis cases and often represent the initial signs of severe reactions 1, 3
• Recognize that cutaneous findings may be delayed or absent in rapidly progressive anaphylaxis—pruritus with hypotension or respiratory symptoms mandates treatment as anaphylaxis 1
• The more rapidly symptoms develop, the more likely the reaction is severe and potentially life-threatening 1

Immediate Management Based on Severity

If Anaphylaxis is Present or Suspected (Pruritus + Respiratory/Cardiovascular Symptoms)

Epinephrine is the only first-line treatment and must never be delayed:

• Administer epinephrine 0.3-0.5 mg (1 mg/mL) intramuscularly into the anterolateral mid-thigh immediately 2, 4
• Repeat every 5-15 minutes if severe hypotension, bronchospasm, or progressive symptoms persist 2, 5
• Position patient supine with legs elevated if hypotensive (or in position of comfort if respiratory distress) 2, 4
• Administer aggressive IV fluid resuscitation with normal saline 1-2 L at 5-10 mL/kg in first 5 minutes for hypotension 2
• Provide supplemental oxygen for any respiratory symptoms 2, 4

After epinephrine administration, consider adjunctive therapies:

• H1 antihistamine: diphenhydramine 50 mg IV to address cutaneous symptoms 2, 5
• H2 antihistamine: ranitidine 50 mg IV or famotidine 20 mg IV 1, 2
• Note: Corticosteroids have no role in treating acute anaphylaxis due to slow onset and do not prevent biphasic reactions 2, 5

If Isolated Pruritus Without Systemic Features (Mild Hypersensitivity)

For pruritus with urticaria/flushing but no respiratory or cardiovascular involvement:

• Monitor vital signs for ≥15 minutes to detect progression 1
• Administer H1 antihistamine: diphenhydramine 50 mg IV or cetirizine 10 mg IV/PO 1
• Consider H2 antagonist: famotidine 20 mg IV for additional mast cell blockade 1
• Consider hydrocortisone 100-500 mg IV for persistent symptoms, though benefit is delayed 1
• Maintain IV access with normal saline at keep-vein-open rate 1

Critical Observation Period

All patients with hypersensitivity reactions require extended monitoring:

• Observe for minimum 4-6 hours after symptom resolution for most patients 2, 5
• Extend observation to 6+ hours or admit patients with:
  • Severe initial symptoms requiring epinephrine 2, 5
  • Multiple doses of epinephrine needed 5
  • Cardiovascular collapse or hypotension 5
  • Unknown trigger 5
• Biphasic reactions occur in 1-23% of cases, typically around 8 hours but can occur up to 72 hours later 5

Common Pitfalls to Avoid

Critical errors that increase morbidity and mortality:

• Never delay epinephrine while administering antihistamines or corticosteroids first—this is the most dangerous error and contributes to fatalities 2, 4
• Do not rely on antihistamines alone to treat evolving anaphylaxis—they cannot address cardiovascular collapse or respiratory distress 4
• Do not discharge patients prematurely before complete symptom resolution and adequate observation period 2, 5
• Do not assume absence of urticaria excludes anaphylaxis—cutaneous findings may be delayed or absent in 25% of cases 1, 3
• Recognize that "feeling odd" or "impending doom" may be the only early warning before full cardiovascular collapse 1, 2

Discharge Criteria and Follow-Up

Patients may only be discharged after:

• Complete resolution of all symptoms 2, 5
• Completion of appropriate observation period based on severity 2, 5
• Hemodynamic stability without ongoing interventions 5

At discharge, provide:

• Epinephrine auto-injector prescription with written emergency action plan 2, 5
• Referral to allergist for comprehensive evaluation and trigger identification 2, 4
• Education on anaphylaxis recognition, trigger avoidance, and proper auto-injector use 2, 4

Special Considerations

Distinguish between true anaphylaxis and other reactions:

• Vasovagal reactions mimic anaphylaxis but present with bradycardia rather than tachycardia and lack cutaneous manifestations 2
• If doubt exists about whether this is anaphylaxis, it is generally better to administer epinephrine 1
• Document timing of symptom onset, vital signs, and response to treatment for specialist referral 6