What is the appropriate management for an adult patient with no known severe allergies or medical conditions experiencing an allergic reaction?

Management of Allergic Reactions in Adults

For any adult experiencing an allergic reaction with symptoms involving more than just isolated skin findings, administer intramuscular epinephrine 0.3-0.5 mg into the anterolateral thigh immediately—this is first-line treatment and should never be delayed. 1, 2

Immediate Assessment and Treatment

Recognize Anaphylaxis Criteria

Anaphylaxis occurs when symptoms involve two or more organ systems or when there is acute onset of hypotension, respiratory compromise, or persistent gastrointestinal symptoms after allergen exposure. 3, 4

Key symptoms indicating need for epinephrine include: 2, 3

• Respiratory: Difficulty breathing, wheezing, throat tightness, laryngospasm, bronchospasm
• Cardiovascular: Hypotension, tachycardia, syncope, weak pulse
• Skin plus other systems: Urticaria/angioedema combined with respiratory or GI symptoms
• Gastrointestinal: Vomiting, diarrhea, abdominal cramps (when combined with other symptoms)

First-Line Treatment: Epinephrine

Dosing: 2

• Adults ≥30 kg: 0.3-0.5 mg (0.3-0.5 mL of 1:1000 solution) intramuscularly
• Route: Intramuscular injection into the anterolateral thigh (never buttocks, digits, hands, or feet)
• Repeat: Every 5-10 minutes as necessary if symptoms persist or progress

Critical point: Epinephrine has no absolute contraindications in anaphylaxis—the risk of death from untreated anaphylaxis outweighs concerns about cardiovascular side effects, even in patients with heart disease. 1, 2, 5

Adjunctive Medications (Secondary to Epinephrine)

Only after epinephrine administration, consider: 1

• H1 antihistamine: Diphenhydramine 25-50 mg IV/IM or orally
• H2 antihistamine: Ranitidine 50 mg IV or 150 mg orally (H1 and H2 work better together than either alone) 1
• Corticosteroids: Methylprednisolone 125 mg IV or prednisone 40-60 mg orally (may prevent biphasic reactions, though evidence is limited) 1
• Beta-2 agonists: Albuterol for bronchospasm (adjunct only, not replacement for epinephrine) 1
• IV fluids: 10-20 mL/kg bolus for hypotension 1
• Oxygen: Supplemental oxygen for hypoxia 1

Common pitfall: Using antihistamines alone without epinephrine is the most common error and significantly increases risk of progression to life-threatening reactions. 1, 3

Management of Mild Reactions

For isolated mild symptoms (few hives, mild flushing, oral allergy syndrome without progression): 1

• Oral H1 antihistamine (diphenhydramine 25-50 mg or non-sedating second-generation antihistamine)
• Mandatory observation for at least 1-2 hours to monitor for progression
• Administer epinephrine immediately if symptoms progress or involve additional organ systems
• If patient has history of prior severe reactions, lower threshold for epinephrine use 1

Observation Period

After successful treatment, observe for: 1, 3

• Minimum 4-6 hours for most anaphylactic reactions
• Up to 12 hours for patients with:
  • History of biphasic reactions
  • Severe initial presentation
  • Delayed epinephrine administration
  • Ongoing symptoms despite treatment

Biphasic reactions (recurrence without re-exposure) occur in up to 20% of cases, with symptoms starting as late as 6 hours after initial reaction. 1, 3

Refractory Anaphylaxis

If inadequate response to initial epinephrine: 1

• Repeat epinephrine every 5-10 minutes
• Aggressive IV fluid resuscitation (may require liters of crystalloid)
• Consider vasopressors (norepinephrine, dopamine)
• Glucagon 1-5 mg IV for patients on beta-blockers who are epinephrine-unresponsive 1
• Transfer to intensive care unit immediately

Discharge Planning

Before discharge, every patient must receive: 1, 6

1. Epinephrine auto-injector prescription with hands-on training in proper use
2. Written emergency action plan detailing:
   • How to recognize anaphylaxis symptoms
   • When and how to use epinephrine
   • Emergency contact numbers
3. Continuation medications for 2-3 days: 1
   • H1 antihistamine (diphenhydramine every 6 hours or daily non-sedating antihistamine)
   • H2 antihistamine (ranitidine twice daily)
   • Corticosteroid (prednisone 40-60 mg daily)
4. Medical identification jewelry or anaphylaxis wallet card
5. Referral to allergist/immunologist for identification of trigger and long-term management 1, 6

Patients should be instructed: 1

• Potential for delayed reactions up to 24 hours (loose stools, recurrent urticaria, eczema flare)
• Strict avoidance of suspected trigger until allergist evaluation
• When to return to emergency department (any recurrence of symptoms)

Special Considerations

Patients at higher risk for severe reactions: 1, 3

• Coexisting asthma (especially poorly controlled)
• Cardiovascular disease
• Taking beta-blockers or ACE inhibitors
• History of prior severe anaphylaxis
• Mast cell disorders

For these patients: Lower threshold for epinephrine administration and longer observation periods (up to 12 hours). 1, 3