What is the immediate treatment for anaphylaxis?

Immediate Treatment for Anaphylaxis

Administer intramuscular epinephrine immediately into the anterolateral thigh at the first recognition of anaphylaxis—this is the single most critical intervention that saves lives, and delaying its administration is directly associated with fatal outcomes. 1, 2

First-Line Treatment: Epinephrine

Epinephrine is the only first-line medication for anaphylaxis with no absolute contraindications, even in elderly patients with cardiac disease, complex congenital heart disease, or pulmonary hypertension. 1, 2

Dosing and Administration

• Adults: Administer 0.3-0.5 mg (0.01 mg/kg, maximum 0.5 mg) of 1:1000 concentration (1 mg/mL) intramuscularly into the vastus lateralis (anterolateral thigh) 1

• Children: Administer 0.01 mg/kg intramuscularly, with a maximum single dose of 0.3 mg 1

• Autoinjector dosing: 0.15 mg for children 10-25 kg; 0.3 mg for patients ≥25 kg or >30 kg; 0.1 mg for infants where available 2

• Repeat dosing: Epinephrine can and should be repeated every 5-15 minutes as needed if symptoms persist or recur 1, 2

Why Intramuscular in the Thigh?

The anterolateral thigh (vastus lateralis) is superior to subcutaneous or deltoid administration because it achieves faster and higher plasma epinephrine concentrations. 1, 2 This pharmacokinetic advantage translates to more rapid clinical response in the acute setting.

Concurrent Immediate Interventions

While preparing and administering epinephrine, simultaneously implement these measures:

• Position the patient supine with legs elevated (unless respiratory distress is present, in which case allow them to sit upright) 2

• In pregnant women, perform left uterine displacement to avoid aortocaval compression 2

• Administer supplemental oxygen 2

• Establish intravenous access immediately 2

• Stop any ongoing allergen exposure (e.g., discontinue IV medication or contrast infusion) 1

Fluid Resuscitation

Aggressive fluid resuscitation is imperative to combat vasodilation and capillary leak:

• Grade II reactions: Initial bolus of 0.5 L crystalloids 2

• Grade III reactions: Initial bolus of 1 L crystalloids 2

• Repeat boluses as needed up to 20-30 mL/kg based on clinical response 2

Refractory or Severe Anaphylaxis

If the patient does not respond to initial intramuscular epinephrine and fluid resuscitation:

• Consider IV epinephrine: When an IV line is in place, administer 0.05-0.1 mg (50-100 μg) of 1:10,000 concentration (0.1 mg/mL) as a bolus 1

• Epinephrine infusion: For protracted anaphylaxis or after more than three epinephrine boluses, initiate continuous infusion at 0.05-0.1 μg/kg/min (5-15 μg/min in adults) 1, 2

• Alternative vasopressors: For persistent hypotension despite epinephrine, consider norepinephrine, vasopressin, phenylephrine, or metaraminol 2

• Patients on beta-blockers: May require glucagon IV 1-2 mg due to potential epinephrine resistance 2

Second-Line Adjunctive Therapies (NOT Substitutes for Epinephrine)

These medications should NEVER delay or replace epinephrine administration—they are supplemental only after epinephrine has been given: 1, 2

• H1 antihistamines: Diphenhydramine or chlorphenamine 25-50 mg IV addresses only cutaneous symptoms and does not prevent or reverse cardiovascular collapse or airway obstruction 1, 2

• H2 antihistamines: Ranitidine 50 mg IV (adults) may be considered, though high-quality evidence supporting this practice is lacking 1

• Bronchodilators: Inhaled beta-2 agonists for persistent bronchospasm after epinephrine 1

• Glucocorticoids have NO role in acute anaphylaxis due to slow onset of action and lack of evidence for preventing biphasic reactions 1

Critical Pitfalls to Avoid

• Never delay epinephrine to administer antihistamines or steroids—this delay is associated with fatal outcomes 1, 2

• Do not administer epinephrine subcutaneously or into the deltoid—intramuscular thigh injection is pharmacologically superior 1, 2

• Do not assume a single dose of epinephrine is sufficient—approximately 10-35% of patients require repeat dosing 1, 2

• Do not discharge patients prematurely—observe for minimum 6 hours in a monitored setting capable of managing recurrent anaphylaxis 1, 2

Post-Stabilization Management

• Observe all patients until symptoms fully resolve, with minimum observation of 6 hours for most patients 1, 2

• Patients requiring >1 dose of epinephrine or with severe initial presentation should be observed for extended periods (up to 6 hours or more) or admitted to ICU due to higher risk of biphasic reactions (odds ratio 4.82) 1, 2

• 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

• Discharge all patients with two epinephrine autoinjectors and a written anaphylaxis emergency action plan 2

• Refer to an allergist for trigger identification and long-term management 1, 2

Special Populations

Cardiac arrest from anaphylaxis: Follow standard BLS/ACLS protocols with immediate epinephrine administration (1 mg IV/IO of 1:10,000 concentration) as the priority intervention 1