What is the immediate treatment for a patient with anaphylaxis, particularly one with a history of allergies and previous anaphylactic reactions?

Immediate Treatment of Anaphylaxis

Administer intramuscular epinephrine 0.3-0.5 mg (0.01 mg/kg in children, maximum 0.3 mg) into the mid-outer thigh immediately upon recognition of anaphylaxis—this is the single most critical intervention that saves lives. 1, 2, 3

First-Line Treatment: Epinephrine Administration

Epinephrine is the only first-line medication for anaphylaxis and must never be delayed or substituted with antihistamines or corticosteroids. 1, 2

Dosing and Route

• Adults and adolescents ≥50 kg: 0.3-0.5 mg intramuscular (1:1000 concentration) 2, 3
• Prepubertal children or <30 kg: 0.01 mg/kg intramuscular, maximum 0.3 mg 2, 3
• Inject into the mid-outer thigh (vastus lateralis muscle) for optimal absorption—this produces higher and more rapid peak plasma levels than deltoid or subcutaneous routes 2, 4
• Never inject into buttocks, digits, hands, or feet due to risk of tissue necrosis 3

Repeat Dosing

• Repeat epinephrine every 5-15 minutes if symptoms persist or recur—approximately 6-19% of pediatric patients and 17% of all patients require a second dose 2, 4
• Do not hesitate to give multiple doses; failure to inject epinephrine promptly contributes to anaphylaxis fatalities 5

Immediate Supportive Measures (Simultaneous with Epinephrine)

Patient Positioning

• Place patient supine with lower extremities elevated to maintain cerebral perfusion 2, 4
• Never allow the patient to stand, walk, or run—sudden postural changes can precipitate cardiovascular collapse and death 2
• If respiratory distress or vomiting is present, position for comfort while maintaining airway 2

Activate Emergency Response

• Call emergency medical services (911) immediately when anaphylaxis is suspected 2
• In hospital settings, activate the resuscitation team while simultaneously treating 1

Adjunctive Treatments (Only AFTER Epinephrine)

Oxygen and Airway Management

• Administer supplemental oxygen at 6-8 L/min for patients with respiratory symptoms 2, 4
• Assess for rapidly progressive laryngeal edema—prepare for emergency intubation if stridor worsens 4
• Consider early intubation before complete airway obstruction occurs; delayed intubation may necessitate emergency cricothyroidotomy 4

Intravenous Fluid Resuscitation

• Establish large-bore IV access and administer normal saline rapidly 2, 4
• Adults: 5-10 mL/kg in first 5 minutes (1-2 L total), up to 30 mL/kg in first hour if needed 2
• Children: 20 mL/kg rapid bolus, repeat as needed for persistent hypotension 4
• Large volumes may be necessary—anaphylaxis can cause massive fluid shifts 1

Bronchodilators

• Albuterol nebulizer or MDI may be used for persistent bronchospasm after epinephrine administration 2
• Inhaled beta-2 agonists are adjunctive only and never substitute for epinephrine 1

Second-Line Medications (Never Delay Epinephrine)

Antihistamines

• H1-antihistamines (diphenhydramine 1 mg/kg IV or chlorphenamine 0.2 mg/kg IV) may be given after adequate epinephrine and fluid resuscitation 4
• H2-antihistamines (ranitidine 1 mg/kg IV or famotidine 0.25 mg/kg IV) can be added but provide no immediate benefit 4
• Antihistamines should never delay or substitute for epinephrine—they do not prevent or relieve airway obstruction or shock 1, 2

Corticosteroids

• Methylprednisolone 1-2 mg/kg IV or hydrocortisone 5 mg/kg IV may be administered after adequate resuscitation 1, 4
• Corticosteroids have no role in acute management but may prevent biphasic reactions (though evidence is limited) 4
• Never delay epinephrine to give corticosteroids 1

Management of Refractory Anaphylaxis

Persistent Hypotension Despite Epinephrine and Fluids

• Consider IV epinephrine infusion: 0.05-0.1 mcg/kg/min, or 5-10 mcg boluses 4
• Alternative vasopressors: vasopressin, norepinephrine, metaraminol, or phenylephrine if epinephrine alone is insufficient 1
• Continuous hemodynamic monitoring is mandatory for IV epinephrine or vasopressor infusions 2

Patients on Beta-Blockers

• Glucagon 1-5 mg IV over 5 minutes, followed by 5-15 mcg/min infusion for patients resistant to epinephrine due to beta-blocker therapy 2
• Note: Rapid glucagon administration can induce vomiting (not epinephrine) 2
• Consider extracorporeal life support if skills and equipment are available 1

Observation and Monitoring

Duration of Observation

• Minimum 4-6 hours observation in a monitored setting for all patients after successful treatment 2, 4
• Prolonged observation or ICU admission is warranted for: 1, 4
  • Severe anaphylaxis (Grades III-IV reactions)
  • Patients requiring >1 dose of epinephrine
  • Ongoing vasopressor requirements
  • History of biphasic reactions
  • Coexisting severe asthma

Biphasic Reactions

• Risk factors for biphasic reactions include: severe initial anaphylaxis, need for multiple epinephrine doses, and delayed epinephrine administration 1
• Biphasic reactions occur in up to 20% of cases, typically within 4-12 hours 6

Diagnostic Testing

Mast Cell Tryptase

• Obtain serial tryptase levels to confirm anaphylaxis diagnosis when clinical presentation is unclear 1, 4
• Timing: First sample at 1 hour after reaction onset, second at 2-4 hours, and baseline sample at least 24 hours post-reaction 1, 4
• Elevated tryptase reflects mast cell degranulation but is not required for diagnosis or treatment 1

Discharge Planning and Follow-Up

Mandatory Prescriptions and Education

• Prescribe two epinephrine autoinjectors with hands-on training on proper use before discharge 2, 4
• Provide written anaphylaxis emergency action plan detailing triggers, symptoms, and when to use epinephrine 1, 2
• Refer to board-certified allergist for comprehensive evaluation and identification of triggers 2, 4

Patient Education Must Include

• Recognition of early anaphylaxis symptoms (throat tightness, difficulty breathing, dizziness, hives) 2
• Proper autoinjector technique and importance of immediate use 1
• Trigger avoidance strategies 2
• Medical identification jewelry (MedicAlert bracelet) 1
• Risk of biphasic reactions and need for emergency department evaluation even after successful autoinjector use 2

High-Risk Populations Requiring Heightened Vigilance

Patients at increased risk for severe or fatal anaphylaxis include: 2, 6

• Adolescents and young adults
• Those with coexisting asthma (especially severe or poorly controlled)
• Previous history of anaphylaxis
• Peanut or tree nut allergies
• Underlying cardiovascular disease
• Patients on beta-blockers or ACE inhibitors
• Mast cell disorders

These patients require immediate epinephrine autoinjector prescriptions and aggressive early treatment. 2

Critical Pitfalls to Avoid

• Never delay epinephrine while waiting for IV access or giving antihistamines—delays in epinephrine administration are associated with increased mortality 2, 5
• Never use subcutaneous epinephrine—intramuscular injection provides faster and more reliable absorption 5
• Never allow patients to remain upright or walk—this can precipitate fatal cardiovascular collapse 2
• Never discharge patients without epinephrine autoinjectors and written action plans 2, 4
• Never rely on antihistamines or asthma inhalers alone—these cannot prevent or reverse airway obstruction or shock 1

Special Considerations for Pregnancy

• Management follows identical principles—epinephrine remains the drug of choice despite pregnancy 1
• Position with left uterine displacement to avoid aortocaval compression 1
• Consider emergent Caesarean delivery if persistent hypotension despite resuscitation 1
• Perimortem Caesarean delivery within 5 minutes if cardiac arrest persists despite resuscitation 1