What is the first-line treatment for a patient experiencing anaphylaxis?

Treatment for Anaphylaxis

Intramuscular epinephrine 0.01 mg/kg (maximum 0.5 mg in adults, 0.3 mg in children) injected into the mid-outer thigh (vastus lateralis) is the immediate first-line treatment for anaphylaxis and must be administered without delay. 1, 2, 3, 4

Immediate Recognition and Action

Stop any ongoing allergen exposure (such as contrast infusion) and activate emergency medical services immediately while simultaneously beginning treatment. 1, 2, 3

The diagnosis of anaphylaxis is purely clinical and requires no laboratory confirmation before treatment. 2, 3 Key features distinguishing anaphylaxis from vasovagal reactions include the presence of cutaneous symptoms (urticaria, angioedema, flushing, pruritus) and tachycardia rather than bradycardia, though bradycardia can rarely occur late in anaphylaxis due to cardioinhibitory reflex. 1

First-Line Treatment: Epinephrine Administration Protocol

Dosing

• Adults and adolescents >50 kg: 0.3-0.5 mg intramuscular (1:1000 concentration = 1 mg/mL) 1, 2, 3, 4
• Prepubertal children: 0.01 mg/kg intramuscular, maximum 0.3 mg 1, 2, 3
• Infants: 0.15 mg dose is widely prescribed, though 0.1 mg autoinjectors provide greater accuracy for smaller infants 1

Route and Site

Inject into the vastus lateralis muscle (mid-outer thigh) for optimal absorption. 1, 2, 3 Intramuscular injection in the thigh produces higher and more rapid peak plasma epinephrine levels compared to deltoid (arm) or subcutaneous routes. 2, 3 Subcutaneous administration delays onset of action and should be avoided. 5

Repeat Dosing

Repeat epinephrine every 5-15 minutes if symptoms persist or recur. 1, 2, 3 Approximately 6-19% of patients require a second dose. 2, 3 There are no absolute contraindications to epinephrine use in anaphylaxis, including in elderly patients, those with cardiac disease, or patients on beta-blockers. 1, 3

Critical Pitfall

Delayed epinephrine administration is the single most important risk factor for anaphylaxis fatalities and biphasic reactions. 1, 3 Never delay epinephrine while administering antihistamines, corticosteroids, or waiting to "see if symptoms improve." 3

Patient Positioning

Place the patient supine with lower extremities elevated to optimize venous return and prevent cardiovascular collapse. 2, 3 If respiratory distress or vomiting is present, position for comfort. 2 Never allow the patient to stand, walk, or run, as sudden postural changes can precipitate fatal cardiovascular collapse. 2

Adjunctive Treatments (Only AFTER Epinephrine)

These are second-line therapies that should never substitute for or delay epinephrine administration. 1, 2, 3

Oxygen and Airway Management

• Supplemental oxygen at 6-8 L/min for patients with respiratory symptoms or those requiring multiple epinephrine doses 2, 3
• Consider endotracheal intubation or cricothyrotomy if airway compromise is severe 2

Fluid Resuscitation

• Establish IV access and administer normal saline rapidly for hypotension or incomplete response to epinephrine 1, 2, 3
• Adults: 5-10 mL/kg in first 5 minutes (1-2 L total) 2
• Children: up to 30 mL/kg in first hour 2

Bronchodilators

• Albuterol nebulizer or MDI for persistent bronchospasm after epinephrine 2, 3

Antihistamines

• H1 antihistamines (diphenhydramine) and H2 antihistamines address only cutaneous manifestations and have no effect on life-threatening cardiovascular or respiratory symptoms 1, 2
• Use oral liquid formulations for more rapid absorption than tablets 2
• These medications are considered solely second-line therapy 1

Glucocorticoids

• May help prevent protracted or biphasic reactions but provide no benefit in acute treatment 2

Refractory Anaphylaxis

For patients not responding to initial epinephrine and fluids:

• Intravenous epinephrine infusion (1:10,000 concentration) may be necessary in rare cases of protracted anaphylaxis 1
• Add 1 mg epinephrine to 1000 mL normal saline; start at 2 mcg/min (120 mL/h) and titrate up to 10 mcg/min (600 mL/h) based on blood pressure, heart rate, and oxygenation 1
• Vasopressor infusion (dopamine) for persistent hypotension with continuous hemodynamic monitoring 2
• For patients on beta-blockers: Glucagon 1-5 mg IV over 5 minutes, followed by 5-15 mcg/min infusion 2

Observation and Transfer

All patients must be transferred to an emergency department for observation, preferably by EMS vehicle. 2, 3 This applies even to patients who respond well to initial treatment. 2, 3

• Minimum observation period: 4-6 hours after symptom resolution 2, 3
• Extended observation or admission is warranted for severe anaphylaxis, requirement of multiple epinephrine doses, history of biphasic reactions, or patients with poorly controlled asthma 2, 3
• Delayed deterioration occurs in 17% of anaphylaxis cases, with 69% occurring within 4 hours of ED arrival 1

Discharge Planning

Before discharge from emergency care:

• Prescribe two epinephrine autoinjectors with hands-on training in proper use 2, 3
• Provide written anaphylaxis emergency action plan 2, 3
• Refer to an allergist for trigger identification and long-term management 2, 3
• Educate on biphasic reaction risk (symptoms recurring after initial resolution) and when to re-administer epinephrine 2, 3

High-Risk Populations Requiring Heightened Vigilance

Patients at increased risk for severe or fatal anaphylaxis include:

• Adolescents and young adults 2, 3
• Patients with concomitant asthma, especially severe or poorly controlled 2, 3
• Previous history of anaphylaxis 2, 3
• Peanut/tree nut allergies 2
• Patients on beta-blockers (may be resistant to epinephrine and require glucagon) 2

These patients require epinephrine autoinjector prescriptions and enhanced education on recognition and immediate treatment. 2, 3