What is the treatment for anaphylaxis?

Treatment of Anaphylaxis

Immediately administer intramuscular epinephrine 0.01 mg/kg of 1:1000 concentration (maximum 0.5 mg in adults, 0.3 mg in children) into the anterolateral thigh—this is the first-line, life-saving treatment with no absolute contraindications. 1, 2

Immediate First-Line Management

Stop the Trigger and Give Epinephrine

• Discontinue any ongoing infusion or exposure to the suspected allergen immediately 1, 3
• Inject epinephrine intramuscularly into the vastus lateralis muscle in the anterolateral thigh for optimal absorption 1, 2, 3
• The FDA-approved indication for intramuscular epinephrine is emergency treatment of Type I allergic reactions including anaphylaxis 4
• Repeat epinephrine every 5-15 minutes as needed if symptoms persist or blood pressure remains unstable 2, 3

Epinephrine Dosing Specifics

• Adults and children >50 kg: 0.5 mg maximum single dose 1
• Children: 0.01 mg/kg of 1:1000 solution 1, 2
• Autoinjector dosing: 0.15 mg for 10-25 kg, 0.30 mg for ≥25 kg, 0.1 mg for infants where available 2
• For infants >7.5 kg where 0.1 mg autoinjectors are unavailable, use 0.15 mg dose 2

Critical Rationale

Epinephrine counteracts the cascade of mediators released during anaphylaxis and arrests further mediator release, preventing and relieving upper and lower airway obstruction and shock 1, 5. Delayed epinephrine administration is associated with increased mortality and biphasic reactions 1, 3. There are no absolute contraindications to epinephrine in anaphylaxis, even in elderly patients, those with cardiac disease, frailty, complex congenital heart disease, or pulmonary hypertension 1, 2, 3.

Supportive Measures (After Epinephrine)

Airway, Breathing, Circulation

• Establish and maintain airway patency 3
• Administer oxygen at 6-8 L/min 3
• Establish intravenous access and begin fluid resuscitation with normal saline immediately for hypotension 1, 3
• Position the patient supine (or in position of comfort if respiratory distress) 3

Escalation for Severe or Refractory Anaphylaxis

When Initial Epinephrine Fails

• For persistent hypotension after 2-3 intramuscular doses, consider intravenous epinephrine 1, 2, 3
• Use 1:10,000 concentration (1 mg/10 mL) administered slowly: 20 μg for Grade II reactions, 50-100 μg for Grade III reactions 2, 3
• For protracted anaphylaxis requiring >3 epinephrine boluses, initiate epinephrine infusion at 0.05-0.1 μg/kg/min (concentration 4.0 μg/mL, infuse at 1-4 μg/min, maximum 10 μg/min) 2, 3

Special Consideration: Beta-Blocker Patients

• For patients on beta-blockers unresponsive to epinephrine, administer glucagon 1-5 mg intravenously over 5 minutes, followed by infusion of 5-15 μg/min 3

Adjunctive Therapies (Secondary to Epinephrine)

Antihistamines

• H1 antihistamines (diphenhydramine or chlorphenamine 25-50 mg IV) are adjunctive for cutaneous symptoms only 2, 3
• H2 antihistamines (ranitidine 50 mg IV in adults) can be added after adequate epinephrine and fluid resuscitation 2
• Never administer antihistamines before or in place of epinephrine—they do not prevent or relieve airway obstruction or shock 2

Bronchodilators

• For persistent bronchospasm, consider inhaled beta-2 agonists after epinephrine administration 3, 6

Corticosteroids

• Glucocorticosteroids may help prevent biphasic or protracted reactions but have no role in acute symptom relief 1, 6

Post-Acute Management and Monitoring

Observation Period

• Observe all patients for minimum 6 hours in a monitored setting, or until stable with regressing symptoms 2, 3
• Individualize observation up to 12 hours for severe reactions or risk factors for biphasic reactions 3, 7
• Biphasic reactions can occur up to 72 hours after initial reaction and are associated with greater initial severity 3

Diagnostic Testing

• Obtain mast cell tryptase levels: first sample at 1 hour after reaction onset, second at 2-4 hours, and baseline sample at least 24 hours post-reaction 2

Critical Pitfalls to Avoid

Distinguishing Anaphylaxis from Vasovagal Reactions

• Vasovagal reactions present with bradycardia (not tachycardia) and lack cutaneous manifestations (urticaria, angioedema, flushing, pruritus) 1, 3
• In anaphylaxis, tachycardia precedes any bradycardia; in vasovagal reactions, bradycardia occurs immediately 1
• Patients prone to vasovagal reactions are not candidates for premedication and should not receive epinephrine 1

Route of Administration Matters

• Intramuscular injection in the thigh is superior to subcutaneous (delayed onset) or intravenous routes (increased adverse effects risk) for initial treatment 5, 8
• Autoinjectors minimize dosing errors when staff experience is limited 1

Don't Delay for Diagnostic Certainty

• Anaphylaxis is a clinical diagnosis—do not wait for laboratory confirmation to administer epinephrine 7, 6