What is the appropriate treatment for an anaphylactic reaction?

Treatment of Anaphylactic Reaction

Immediately administer intramuscular epinephrine 0.3-0.5 mg (0.01 mg/kg in children, maximum 0.3 mg) into the mid-outer thigh as soon as anaphylaxis is recognized—this is the only first-line treatment that prevents death from cardiovascular collapse and airway obstruction. 1, 2, 3

Immediate Management (First 5 Minutes)

ABC Approach and Epinephrine Administration

• Call for help immediately and activate emergency medical services while simultaneously beginning treatment 4, 1
• Remove all potential causative agents (foods, medications, IV colloids, latex) 4
• Administer 100% oxygen and maintain airway patency; intubate if necessary 4
• Position patient supine with legs elevated unless respiratory distress or vomiting is present, in which case position for comfort 1, 2
  • Never allow the patient to stand or walk, as this can precipitate cardiovascular collapse 1
  • In pregnant women, perform left uterine displacement to avoid aortocaval compression 2

Epinephrine Dosing (First-Line Treatment)

Adults and adolescents >50 kg:

• 50 μg IV (0.5 mL of 1:10,000 solution) if IV access already established in monitored setting 4
• 500 μg IM (0.5 mL of 1:1,000 solution) into anterolateral thigh if no IV access 4, 1, 2

Children:

• 0.01 mg/kg IM (maximum 0.3 mg) using 1:1,000 solution 4, 1, 2
• Age-based dosing: >12 years: 500 μg IM; 6-12 years: 300 μg IM; <6 years: 150 μg IM 4

Critical point: Intramuscular injection in the anterolateral thigh achieves peak plasma concentrations in 8±2 minutes compared to 34±14 minutes with subcutaneous administration 2, 5

Repeat Dosing

• Repeat epinephrine every 5-15 minutes if symptoms persist or recur 1, 2, 5
• Approximately 6-19% of pediatric patients and 17% of all patients require a second dose 2
• If multiple doses required (>3 boluses), consider epinephrine infusion at 0.05-0.1 μg/kg/min 2

Aggressive Fluid Resuscitation

• Establish IV access immediately and administer normal saline or lactated Ringer's solution rapidly 4
• Adults: 5-10 mL/kg in first 5 minutes (1-2 L total); initial bolus 0.5-1 L depending on severity 2
• Children: Up to 30 mL/kg in first hour; boluses repeated as needed up to 20-30 mL/kg based on clinical response 2
• Large volumes may be required due to vasodilation and capillary leak 4, 2

Secondary Management (Only AFTER Epinephrine)

Adjunctive Medications

H1 Antihistamines:

• Chlorphenamine 10 mg IV (adults) or diphenhydramine 25-50 mg IV 4, 2
• Pediatric dosing: >12 years: 10 mg; 6-12 years: 5 mg; 6 months-6 years: 2.5 mg; <6 months: 250 μg/kg 4
• These treat only cutaneous symptoms and do NOT prevent cardiovascular collapse or airway obstruction 2

H2 Antihistamines:

• Ranitidine 50 mg IV (adults) may be added for additional histamine blockade 2

Corticosteroids:

• Hydrocortisone 200 mg IV (adults) or methylprednisolone 1-2 mg/kg/day IV 4, 2
• Pediatric dosing: >12 years: 200 mg; 6-12 years: 100 mg; 6 months-6 years: 50 mg; <6 months: 25 mg 4
• Do not help in acute treatment but may prevent biphasic reactions 2

Management of Persistent Bronchospasm

• Albuterol nebulizer or MDI for bronchospasm after epinephrine 1, 2
• Consider IV aminophylline or magnesium sulfate for refractory bronchospasm 4

Refractory Anaphylaxis Management

When Standard Treatment Fails

If blood pressure does not recover despite epinephrine and fluids:

• Consider alternative vasopressors: norepinephrine, vasopressin, dopamine, phenylephrine, or metaraminol 4, 2
• Dopamine infusion with continuous hemodynamic monitoring for persistent hypotension 1

For patients on beta-blockers:

• Glucagon 1-5 mg IV over 5 minutes, followed by 5-15 μg/min infusion titrated to response 1, 2
• Rapid glucagon administration can induce vomiting (not epinephrine) 1

Epinephrine infusion preparation:

• Add 1 mg (1 mL) of 1:1,000 epinephrine to 250 mL D5W (concentration 4.0 μg/mL) 2
• Infuse at 0.05-0.1 μg/kg/min (or 1-4 μg/min in adults, increasing to maximum 10 μg/min) 2

Observation and Monitoring

Minimum Observation Period

• Observe for minimum 4-6 hours in a facility capable of managing anaphylaxis 1, 2
• Prolonged observation or ICU admission warranted for severe reactions (Grade III-IV), refractory symptoms, or history of biphasic reactions 1, 2
• Biphasic reactions (symptom recurrence without re-exposure) occur in some patients hours later 1, 2

Mast Cell Tryptase Sampling

• First sample: As soon as feasible after resuscitation starts (do not delay resuscitation) 4
• Second sample: 1-2 hours after symptom onset 4, 2
• Third sample: At 24 hours or in convalescence for baseline comparison 4, 2
• Label all samples with time and date 4

Discharge Planning and Prevention

Mandatory Prescriptions

• Two epinephrine autoinjectors with proper training on use 1, 2
  • 0.15 mg for children 10-25 kg
  • 0.3 mg for individuals ≥25 kg
  • 0.1 mg for infants where available 2
• Written anaphylaxis emergency action plan including triggers, symptoms, and clear instructions 1, 2

Patient Education

• Delayed epinephrine administration is directly associated with anaphylaxis fatalities—inject at earliest sign of anaphylaxis 2, 5, 6
• Always seek emergency care after using epinephrine, even if symptoms improve 2
• Monitor autoinjector expiration dates as epinephrine degrades over time 2
• Refer to allergist for trigger identification and ongoing risk assessment 1, 2

High-Risk Populations Requiring Heightened Vigilance

• Adolescents and young adults 1, 2
• Patients with coexisting asthma, especially severe or poorly controlled 1, 2, 7
• Previous history of anaphylaxis 1, 2
• Peanut/tree nut allergies 1, 7
• Patients on beta-blockers (may require glucagon) 1, 2

Critical Pitfalls to Avoid

• Never delay epinephrine while establishing IV access—IM injection is faster and safer in most settings 2, 5
• Never substitute antihistamines or corticosteroids for epinephrine—they do not prevent death 1, 2
• Avoid subcutaneous or deltoid injection—anterolateral thigh IM achieves faster, higher plasma levels 2, 5
• Do not use IV epinephrine as first-line unless in monitored setting with existing IV access—risk of overdose and arrhythmias 2
• There are no absolute contraindications to epinephrine in anaphylaxis, even in elderly patients with cardiac disease—the risk of death from untreated anaphylaxis far outweighs theoretical concerns 1, 2