Should patients with anaphylaxis who are not in shock and who improve after a single intramuscular epinephrine (adrenaline) dose be admitted to the hospital?

Observation and Admission Decisions for Anaphylaxis Patients Who Improve After Single Epinephrine Dose

Not all patients with anaphylaxis who improve after a single epinephrine dose require hospital admission, but all require a minimum observation period of 4-6 hours in a facility capable of managing anaphylaxis before discharge can be considered. 1

Risk Stratification for Observation vs. Admission

Patients Who May Be Discharged After 4-6 Hour Observation

For patients without severe risk features who respond completely to a single epinephrine dose and remain asymptomatic, discharge after a 1-hour asymptomatic observation may be reasonable. 1 However, the safer approach is 4-6 hours of observation. 1, 2

These lower-risk patients include those who:

• Required only one epinephrine dose 1
• Did not present with severe initial symptoms (no wide pulse pressure, no cardiovascular compromise) 1
• Have complete resolution of all symptoms 1
• Have reliable access to epinephrine autoinjectors 1
• Have access to emergency medical services 1
• Demonstrate good self-management skills 1

Patients Requiring Extended Observation (Up to 6 Hours) or Admission

Extended observation of up to 6 hours or longer, including hospital admission, is strongly suggested for patients with resolved severe anaphylaxis and/or those who required more than one dose of epinephrine. 1

The number needed to monitor with extended observation to detect one biphasic reaction is 41 (range 18-195) for severe initial presentation and 13 (range 7-27) for patients requiring multiple epinephrine doses. 1

Specific High-Risk Features Warranting Extended Observation or Admission:

• Required >1 dose of epinephrine (strongest predictor of biphasic reaction) 1, 2
• Severe initial presentation including hypotension, respiratory compromise, or cardiovascular instability 1
• Wide pulse pressure at presentation 1
• Unknown anaphylaxis trigger 1
• Drug trigger in children 1
• Cardiovascular comorbidity 1
• Coexisting asthma, especially poorly controlled 1, 2
• Adolescents and young adults with peanut or tree nut allergy 1
• Refractory or protracted symptoms despite treatment 1, 2
• Lack of access to epinephrine or emergency medical services 1
• Poor self-management skills 1

Understanding Biphasic Anaphylaxis Risk

Biphasic reactions occur in 1-20% of anaphylaxis episodes, typically around 8 hours after the initial reaction, though they can occur up to 72 hours later. 1, 2 The mean time to biphasic reaction is approximately 11 hours. 2

If the clinical impression suggests a patient has ≥17% risk of biphasic reaction based on the above risk factors, extended observation of up to 6 hours or longer (including hospital admission) is appropriate. 1

Critical Discharge Requirements (For All Patients)

Regardless of observation duration, all patients must receive before discharge: 1, 2

• Two epinephrine autoinjectors (0.15 mg for 10-25 kg; 0.3 mg for ≥25 kg) with hands-on training 1, 2
• Written anaphylaxis emergency action plan detailing symptoms, triggers, and when to use epinephrine 1, 2
• Education about biphasic reaction risk and instructions to return immediately if symptoms recur 1
• Plan for monitoring autoinjector expiration dates 1
• Referral to an allergist for follow-up evaluation within 1-2 weeks 1

Common Pitfalls to Avoid

Do not discharge patients prematurely based solely on symptom resolution. Biphasic reactions can occur many hours after initial improvement, and patients must remain under observation until the appropriate time period has elapsed. 1, 2

Do not rely on antihistamines or glucocorticoids to prevent biphasic reactions. These medications are not reliable interventions for preventing biphasic anaphylaxis and should never create false reassurance about early discharge. 1

Do not use mandatory fixed observation periods universally. While 4-6 hours is a reasonable minimum, the decision should incorporate individual risk factors, with higher-risk patients requiring longer observation or admission. 1, 3

Ensure patients understand that self-injectable epinephrine must be immediately available and used at the first sign of symptom recurrence, as delayed epinephrine administration in biphasic reactions is associated with increased mortality. 2, 4, 5