How do I prescribe epinephrine (adrenaline) to a patient with a history of anaphylaxis?

How to Prescribe Epinephrine for Anaphylaxis

Prescribe two epinephrine autoinjectors (0.15 mg for patients 15-30 kg; 0.3 mg for patients ≥30 kg) with instructions to inject intramuscularly into the lateral thigh at the first sign of anaphylaxis, repeating every 5-10 minutes if symptoms persist or worsen. 1, 2

Patient Selection for Epinephrine Prescription

All patients with a history of anaphylaxis must be prescribed epinephrine autoinjectors. 1, 2 This includes:

• Patients who have experienced systemic allergic reactions to foods, insect stings, medications, or other triggers 1
• High-risk patients without prior anaphylaxis may also warrant prescription based on specific circumstances (e.g., severe food allergy with asthma) 1

Autoinjector Dosing by Weight

The FDA-approved dosing is straightforward 3:

• Patients <30 kg (66 lbs): 0.15 mg autoinjector 1, 2, 3
• Patients ≥30 kg (66 lbs): 0.3 mg autoinjector 1, 2, 3

Important caveat: For infants weighing <15 kg, the 0.15 mg dose represents approximately twice the weight-based recommendation of 0.01 mg/kg, but this is acceptable because the benefit-to-risk ratio strongly favors treatment over withholding epinephrine. 1 There is no absolute contraindication to epinephrine in anaphylaxis. 1, 2

Prescription Instructions: What to Tell Patients

When to Use the Autoinjector

Instruct patients to inject epinephrine immediately when they recognize anaphylaxis, which includes 1, 2:

• Skin/mucosal symptoms (hives, swelling, itching) PLUS respiratory compromise (throat tightness, difficulty breathing, wheezing) OR hypotension/syncope
• Two or more organ systems involved after allergen exposure (skin, respiratory, cardiovascular, gastrointestinal)
• Isolated hypotension after known allergen exposure (even without skin symptoms, which are absent in 10% of cases)

How to Administer

Inject intramuscularly into the anterolateral thigh (vastus lateralis muscle), through clothing if necessary. 1, 3 This route achieves peak plasma concentrations in 8±2 minutes compared to 34±14 minutes with subcutaneous deltoid injection. 1, 2

Repeat Dosing Protocol

If symptoms fail to resolve or worsen, repeat the injection every 5-10 minutes. 1, 2 Approximately 7-18% of patients require a second dose. 1 There is no maximum number of doses—continue until symptoms resolve or EMS arrives. 2

Critical Safety Instructions

• Call 911 immediately after the first injection, even if symptoms improve 1, 2
• Position the patient supine with legs elevated; never allow standing or walking, as this increases mortality risk 1, 2
• Transport to the emergency department via EMS for observation, even if symptoms completely resolve 1, 2

Why Prescribe Two Autoinjectors

Always prescribe two autoinjectors because 2, 4:

• 7-18% of patients require a second dose before EMS arrival 1
• Delayed epinephrine administration is associated with fatal outcomes 1, 4, 5
• Patients may be far from medical care when anaphylaxis occurs

Documentation and Patient Education

Provide written instructions including 1:

• An anaphylaxis emergency action plan
• Demonstration of proper autoinjector technique (have patient/caregiver practice with a trainer device)
• Recognition of anaphylaxis symptoms
• Emphasis that epinephrine is the only first-line treatment—antihistamines and corticosteroids are adjunctive only 1, 4

Special Populations

Patients with Cardiovascular Disease

Prescribe epinephrine despite cardiac concerns. The risk of death from untreated anaphylaxis far exceeds the risk of epinephrine-related cardiac effects, even in patients taking beta-blockers. 1, 2 There is no absolute contraindication to epinephrine in anaphylaxis. 1, 2

Pregnant Women and Elderly

These patients may be at greater risk for adverse effects from epinephrine, but the prescription is still mandatory because anaphylaxis poses a greater threat. 3

Common Prescribing Pitfalls to Avoid

• Underprescribing: Only prescribing one autoinjector instead of two 2
• Wrong dose selection: Using 0.15 mg for patients ≥30 kg or 0.3 mg for patients <15 kg 1, 3
• Inadequate education: Failing to demonstrate proper technique or provide written instructions 1
• Substituting antihistamines: Suggesting antihistamines as an alternative to epinephrine (they are not) 1, 4
• Delaying prescription: Waiting for "confirmed" allergy testing before prescribing to a patient with clear anaphylaxis history 1

Follow-up Care

Refer all patients to an allergist-immunologist for comprehensive evaluation, trigger identification, and consideration of immunotherapy when appropriate (e.g., venom immunotherapy for insect sting allergy). 1, 2