What is the management of allergic reactions in the Outpatient Department (OPD) and as Inpatient (IP)?

Management of Allergic Reactions in Outpatient and Inpatient Settings

Immediate First-Line Treatment: Epinephrine

Intramuscular epinephrine is the only first-line treatment for anaphylaxis and severe allergic reactions in both outpatient and inpatient settings, and must be administered immediately without delay. 1, 2, 3

Outpatient Department (OPD) Management

Epinephrine Administration:

• Adults and children >25 kg: 0.3 mg epinephrine autoinjector IM into anterolateral thigh 1
• Children 10-25 kg: 0.15 mg epinephrine autoinjector IM into anterolateral thigh 1
• Alternative dosing: Epinephrine 1:1,000 solution at 0.01 mg/kg per dose IM (maximum 0.5 mg per dose) 1
• Repeat doses: Every 5-15 minutes as needed if symptoms persist or progress 1, 2

Critical Decision Point: If you observe any of the following, administer epinephrine immediately without waiting: 1, 3

• Difficulty breathing or wheezing
• Throat tightness or difficulty swallowing
• Hypotension or dizziness
• Generalized urticaria with known allergen exposure
• Any cardiovascular or respiratory symptoms
• History of prior severe reactions (give epinephrine at onset of even mild symptoms) 1

Common Pitfall: The most dangerous error is using antihistamines alone as primary treatment, which delays epinephrine and increases mortality risk. 2, 4 Antihistamines have a much slower onset of action and do not prevent progression to life-threatening anaphylaxis. 2

Adjunctive Treatments in OPD (Only AFTER Epinephrine)

Administer these simultaneously with epinephrine, not sequentially: 1

• H1 antihistamine (Diphenhydramine): 1-2 mg/kg per dose, maximum 50 mg IV or oral (oral liquid absorbs faster than tablets) 1, 2
• Bronchodilator (Albuterol): For wheezing or bronchospasm
  • MDI: 4-8 puffs (child) or 8 puffs (adult), OR
  • Nebulized: 1.5 mL (child) or 3 mL (adult) every 20 minutes or continuously 1
• Supplemental oxygen: For any respiratory distress 1
• IV fluids: Large volume boluses for orthostasis, hypotension, or incomplete response to epinephrine 1, 4
• Patient positioning: Recumbent with lower extremities elevated (improves venous return) 1

Inpatient/Hospital-Based Management

First-Line Treatment Remains Epinephrine IM: 1

• Same dosing as outpatient setting initially
• For refractory hypotension: Consider continuous IV epinephrine infusion with continuous non-invasive blood pressure and heart rate monitoring 1
• Alternative routes if IM unavailable: Endotracheal or intra-osseous epinephrine 1

Enhanced Monitoring and Support: 1

• Continuous vital signs monitoring
• IV epinephrine infusion dosing (if needed): Starting at 0.05-0.1 mcg/kg/min, titrate to response 1
• Aggressive IV fluid resuscitation: 10-20 mL/kg bolus, repeat as needed 1, 5
• Consider vasopressors for persistent hypotension despite epinephrine and fluids 5

For Refractory Cases: 5

• Double epinephrine dose
• Add vasopressin 1-2 IU with or without infusion at 2 IU/hour
• Norepinephrine infusion 0.05-0.5 mcg/kg/min
• Glucagon 1-2 mg if patient is on beta-blockers (these patients may not respond to epinephrine) 2, 5

Adjunctive Medications in Hospital Setting

H1 and H2 Antihistamine Combination (superior to either alone): 2

• H1 (Diphenhydramine): 1-2 mg/kg, maximum 50 mg IV or oral 1, 2
• H2 (Ranitidine or Famotidine): Add concurrently with H1 antihistamine 2

Corticosteroids (for severe reactions): 1

• Prednisone: 1 mg/kg, maximum 60-80 mg orally 2
• Purpose: May prevent biphasic reactions (though evidence is limited) 1

Bronchodilators: Same as outpatient dosing for persistent bronchospasm 1

Observation Period

All patients who receive epinephrine must be observed for 4-6 hours minimum, longer for severe reactions: 1, 4

• Biphasic reactions (recurrence without re-exposure) occur in up to 20% of cases 4
• Extend observation to 12 hours for: 6
  • Severe initial reaction
  • History of biphasic reactions
  • Delayed epinephrine administration
  • Ongoing symptoms despite treatment

Post-Event Management

Immediate Discharge Instructions

Prescribe at discharge: 1

• Two epinephrine auto-injectors with hands-on training 1, 2
• Written anaphylaxis emergency action plan 1
• Medical identification jewelry or wallet card 1

Continue adjunctive medications for 2-3 days: 1

• Diphenhydramine every 6 hours OR non-sedating second-generation antihistamine 1
• Ranitidine twice daily 1
• Prednisone daily 1

Allergy Investigation and Follow-Up

All Grade II-IV reactions and Grade I with generalized urticaria/erythema require specialist referral: 1, 5

Obtain serum tryptase levels: 1, 5

• First sample: 1 hour post-reaction onset
• Second sample: 2-4 hours post-reaction
• Baseline sample: At least 24 hours post-reaction
• Diagnostic criterion: Increase above 1.2 × baseline + 2 μg/L confirms mast cell degranulation 5

Documentation for allergist (critical for accurate diagnosis): 1

• Chronological narrative with exact timing of all exposures
• All substances administered within 1-2 hours before symptom onset
• Complete drug charts including premedication
• "Hidden exposures" (chlorhexidine, excipients, blue dyes, gels, sprays) 1
• Treatment given and response
• Copies of all relevant medical records 1

Allergy testing timeline: 4-6 weeks after reaction 5

Follow-up appointment: With primary care physician and allergist/immunologist 1, 2

Critical Pitfalls to Avoid

1. Never delay epinephrine to give antihistamines first - this is the leading cause of preventable anaphylaxis deaths 2, 4
2. Never use antihistamines alone for any reaction with systemic symptoms 1, 2
3. Never rely on subjective symptoms alone - observe for objective signs before dismissing concerns 1
4. Never discharge without epinephrine auto-injectors and training 1, 2
5. Never assume mild initial symptoms will remain mild - progression can be rapid and unpredictable 1, 4

Special Populations

Patients on beta-blockers: 2, 5

• May have reduced response to epinephrine
• Have glucagon readily available (20-30 mcg/kg for children, 1-5 mg for adults) 2, 5

Patients with cardiovascular disease: 4

• Epinephrine is still indicated - serious adverse effects are rare in otherwise healthy individuals
• Common effects (pallor, tremor, anxiety, palpitations) are expected and transient 4

Patients with prior severe reactions or high-risk allergens (peanuts, tree nuts, seafood): 4

• Administer epinephrine at onset of even mild symptoms 1, 4
• Lower threshold for treatment and longer observation 4