What is the treatment for an anaphylactic reaction?

Treatment of Anaphylactic Reaction

Immediately administer intramuscular epinephrine 0.01 mg/kg (1:1000 concentration, maximum 0.5 mg for adults >50 kg, 0.3 mg for children >30 kg) into the anterolateral thigh—this is the single most critical intervention that saves lives and has no absolute contraindications. 1

Immediate First-Line Management

Epinephrine Administration

• Stop any ongoing allergen exposure (e.g., IV contrast infusion) and give epinephrine immediately—these are the two most important steps 1
• Inject into the vastus lateralis muscle of the anterolateral thigh for optimal absorption, not subcutaneous or deltoid 1, 2
• Use 0.01 mg/kg of 1:1000 (1 mg/mL) concentration with maximum single dose of 0.5 mg for patients >50 kg 1, 3
• For autoinjectors: 0.3 mg for patients >30 kg, 0.15 mg for children 25-30 kg 1, 2
• Repeat every 5-15 minutes if symptoms persist—delay in epinephrine administration is associated with fatalities and biphasic reactions 1
• No absolute contraindications exist, even in elderly patients with cardiac disease, frailty, or complex comorbidities 1, 2

Positioning and Oxygen

• Place patient supine with legs elevated (unless respiratory distress prevents this) to combat vasodilation and capillary leak 2
• In pregnant women, perform left uterine displacement to avoid aortocaval compression 2
• Administer supplemental oxygen for respiratory symptoms or prolonged reactions 1, 2

Fluid Resuscitation

• Establish IV access immediately 2
• For hypotension, give 1 L crystalloid bolus (0.5 L for Grade II reactions, 1 L for Grade III) 2
• Repeat boluses as needed up to 20-30 mL/kg based on clinical response 2
• Change patient position to supine or Trendelenburg for hypotension 1

Management of Refractory Anaphylaxis

When Initial IM Epinephrine Fails

• If no response after 2-3 doses of IM epinephrine, consider IV epinephrine infusion at 0.05-0.1 μg/kg/min (1:10,000 concentration) 1, 2
• Alternative protocol: 1 mg epinephrine in 250 mL D5W (4 μg/mL concentration) infused at 1-4 μg/min, titrating up to 10 μg/min maximum for adults 1
• For children: 0.01 mg/kg (0.1 mL/kg of 1:10,000 solution, maximum 0.3 mg) 1

Alternative Vasopressors

• For persistent hypotension despite epinephrine and fluids, consider norepinephrine, vasopressin, phenylephrine, or metaraminol 2
• Patients on beta-blockers may require glucagon 1-2 mg IV for refractory bronchospasm 2

Second-Line Adjunctive Therapies (Only After Epinephrine)

What NOT to Give First

• Never administer antihistamines, glucocorticoids, or bronchodilators before epinephrine—all other therapies are secondary 1, 2

Antihistamines (Adjunctive Only)

• H1 antihistamines (diphenhydramine 25-50 mg IV) address only cutaneous manifestations, which are not life-threatening 1, 2
• H2 antihistamines (ranitidine 50 mg IV) have no high-quality evidence supporting efficacy in anaphylaxis 1
• These are commonly given but only provide symptomatic relief for urticaria and pruritus 1

Glucocorticoids (NOT Recommended for Acute Phase)

• Do NOT give glucocorticoids for acute anaphylaxis—they have slow onset of action and no role in immediate management 1
• Multiple systematic reviews show no evidence that glucocorticoids prevent biphasic anaphylaxis 1

Bronchodilators

• Inhaled beta-2 agonists (albuterol 2.5 mg) only for bronchospasm refractory to epinephrine 1

Post-Anaphylaxis Management

Observation Period

• Observe for minimum 6 hours in monitored area until stable and symptoms resolved 1, 2
• Patients requiring >1 dose of epinephrine or with severe reactions (Grade III-IV) typically require ICU admission 2
• Biphasic anaphylaxis occurs in 10.3% of cases (mean 11 hours later, up to 72 hours), more likely with severe initial reactions requiring multiple epinephrine doses 1

Diagnostic Testing

• Obtain serum tryptase levels: first sample at 1 hour after onset, second at 2-4 hours, baseline sample at ≥24 hours post-reaction 2

Emergency Response System

• Always activate EMS/emergency response even if symptoms improve with initial epinephrine—patients may require advanced interventions including intubation, IV vasopressors, or extracorporeal life support 1, 2
• Send patients to emergency department for extended observation, as most imaging centers and outpatient facilities cannot provide adequate monitoring 1

Critical Pitfalls to Avoid

• Delaying epinephrine is the most common fatal error—it must be given immediately, not after antihistamines or observation 1, 4, 5
• Subcutaneous or deltoid injection results in delayed absorption compared to anterolateral thigh IM 2, 4
• Placing patient upright can precipitate cardiovascular collapse—keep supine with legs elevated 2, 5
• Withholding epinephrine due to cardiac history—there are no absolute contraindications, and risk of death from untreated anaphylaxis far exceeds any epinephrine risk 1, 2
• Single dose assumption—7-18% of patients require repeat dosing, so have additional epinephrine immediately available 1