What is the appropriate dose of epinephrine (adrenaline) for a patient experiencing anaphylaxis?

Epinephrine 0.3 mg for Anaphylaxis

Epinephrine 0.3 mg intramuscularly in the anterolateral thigh is the correct dose for adults and children weighing ≥25-30 kg (55-66 lbs) experiencing anaphylaxis, and it should be administered immediately without delay. 1, 2

Dosing by Weight

Adults and Larger Children

• Adults and children ≥30 kg (66 lbs): 0.3-0.5 mg (0.3-0.5 mL of 1:1000 concentration) intramuscularly 2
• Children ≥25 kg (55 lbs): 0.3 mg via autoinjector is appropriate, as this provides approximately 0.012 mg/kg—a slight overdose that is preferable to underdosing during life-threatening anaphylaxis 3, 4

Smaller Children

• Children <30 kg: 0.01 mg/kg (maximum 0.3 mg) intramuscularly 3, 2
• Children 10-25 kg: 0.15 mg autoinjector dose 4
• Infants >7.5 kg: 0.15 mg autoinjector, though this represents a higher dose per kilogram than ideal 5

Administration Technique

Route and Site

• Intramuscular injection into the anterolateral thigh (vastus lateralis muscle) is mandatory as it achieves peak plasma concentrations in 8±2 minutes versus 34±14 minutes with subcutaneous injection 3, 4
• Inject at a 90-degree angle perpendicular to the skin to ensure the medication reaches muscle tissue rather than subcutaneous fat 4
• Can be administered through clothing if necessary—do not delay for clothing removal 4

Repeat Dosing

• Repeat every 5-15 minutes if symptoms persist or recur 3, 1, 2
• Approximately 7-19% of patients require a second dose 3, 1
• More frequent dosing intervals can be used if clinically indicated 3

Critical First-Line Treatment Principles

Timing is Everything

• Epinephrine is the ONLY first-line medication for anaphylaxis—there are no acceptable alternatives 3, 5
• Delayed administration is directly associated with fatalities—inject immediately upon recognition of anaphylaxis 3, 5
• Do not delay epinephrine to administer antihistamines, corticosteroids, or bronchodilators first 3, 5

No Absolute Contraindications

• There are no absolute contraindications to epinephrine in anaphylaxis, even in elderly patients with cardiac disease, hypertension, or other comorbidities 1, 4, 5
• The benefits of epinephrine always outweigh the risks during anaphylaxis 1, 5
• Common adverse effects (pallor, tremor, anxiety, palpitations) are transient and acceptable given the life-threatening nature of anaphylaxis 1, 4

Adjunctive Treatments (Never First-Line)

Secondary Medications

• H1-antihistamines (diphenhydramine 1-2 mg/kg or 25-50 mg) are adjunctive only for cutaneous symptoms 3, 5
• H2-antihistamines (ranitidine 1 mg/kg IV) may provide additional benefit when combined with H1-antihistamines 3
• Inhaled albuterol (2.5-5 mg nebulized) for bronchospasm resistant to epinephrine 3
• Corticosteroids have NOT been proven to prevent biphasic reactions and may actually worsen outcomes when used without adequate epinephrine 3

Supportive Care

• Position patient supine with legs elevated (unless respiratory distress prevents this) 3, 5
• Administer supplemental oxygen at 6-8 L/min 3
• Establish IV access and give normal saline boluses (adults: 1-2 L; children: up to 30 mL/kg in first hour) for hypotension 3

Refractory Anaphylaxis

IV Epinephrine Infusion

• Reserved for profound hypotension unresponsive to IM epinephrine and fluid resuscitation 1, 4
• Preparation: Add 1 mg (1 mL of 1:1000) to 250 mL D5W, yielding 4 μg/mL concentration 3, 4
• Infusion rate: Start at 1-4 μg/min (15-60 drops/min), titrate up to maximum 10 μg/min 3, 4
• Critical warning: IV bolus epinephrine carries risk of fatal arrhythmias and should only be used during cardiac arrest or when IM epinephrine has failed 3

Post-Treatment Management

Observation Period

• All patients must be observed for 4-6 hours minimum or until symptoms fully resolve and are regressing 3, 5
• Patients requiring >1 dose of epinephrine have higher risk of biphasic reactions 3, 4
• Biphasic reactions can occur up to 72 hours later (mean 11 hours) 4

Discharge Planning

• Prescribe two epinephrine autoinjectors before discharge 5
• Provide written anaphylaxis emergency action plan 3
• Refer to allergist for trigger identification and long-term management 3

Common Pitfalls to Avoid

Dosing Errors

• Do not inject into buttocks, digits, hands, or feet—these sites have poor absorption and risk of tissue injury 2
• Do not use subcutaneous route—absorption is too slow for anaphylaxis 3, 4
• Do not underdose in adults or overdose in small infants due to fixed autoinjector doses 4

Treatment Delays

• Never withhold epinephrine due to fear of adverse effects—the risk of death from untreated anaphylaxis far exceeds any epinephrine-related risks 1, 5
• Do not wait for "perfect" vital signs or complete symptom development—if anaphylaxis is suspected, inject immediately 3
• Do not substitute antihistamines or bronchodilators as first-line treatment—this is a fatal error 5