Anaphylaxis Treatment
Epinephrine administered intramuscularly into the anterolateral thigh at 0.01 mg/kg (maximum 0.5 mg in adults, 0.3 mg in children) is the immediate first-line treatment for anaphylaxis and should never be delayed. 1, 2, 3
Immediate Management Algorithm
Step 1: Epinephrine Administration (First-Line)
- Administer intramuscular epinephrine immediately upon recognition of anaphylaxis—this is the only medication proven to prevent death 1, 2, 3
- Dose: 0.01 mg/kg of 1:1000 solution (maximum 0.5 mg adults, 0.3 mg children) injected into the lateral thigh 1, 2, 3
- Repeat every 5-15 minutes as needed if symptoms persist or recur 1, 2, 3
- Intramuscular route is superior to subcutaneous administration due to faster absorption and more predictable pharmacokinetics 1, 2
- There are no absolute contraindications to epinephrine in anaphylaxis, even in elderly patients with cardiovascular disease 2
Step 2: Supportive Care
- Remove the trigger if still present 3, 4
- Position patient supine with lower limbs elevated; never place upright as this increases mortality risk 5
- Assess and secure airway, breathing, circulation with close hemodynamic monitoring 1
- Prepare for advanced airway management including potential cricothyroidotomy if oropharyngeal/laryngeal edema develops 1
Step 3: Escalation for Severe/Refractory Cases
- Intravenous epinephrine (0.05-0.1 mg or 5-10% of cardiac arrest dose) is reasonable when IV access is established and shock persists 1
- Continuous epinephrine infusion (5-15 μg/min or 0.05-0.1 μg/kg/min) for refractory hypotension after multiple boluses 1, 2
- Aggressive fluid resuscitation for persistent hypotension 1
- Consider vasopressors (dopamine) if hypotension remains refractory to epinephrine and fluids 3
- Glucagon infusion specifically for patients on β-blockers who may be resistant to epinephrine 3
Step 4: Adjunctive Medications (Only AFTER Epinephrine)
- H1 antihistamines (diphenhydramine 25-50 mg IV) for cutaneous symptoms only—never as first-line or monotherapy 1, 2, 3
- H2 antihistamines (ranitidine 50 mg IV) in combination with H1 blockers may provide additional benefit 2, 3
- Nebulized albuterol for bronchospasm resistant to epinephrine 3
- Corticosteroids (1-2 mg/kg/day equivalent) have no role in acute treatment due to delayed onset but may be considered for prolonged reactions or patients with asthma 1, 3
Critical caveat: Antihistamines and corticosteroids do NOT prevent biphasic reactions and should never delay epinephrine administration 1, 3
Post-Resuscitation Management
Observation Period
- Minimum 6 hours observation in a monitored setting capable of managing recurrent anaphylaxis 2
- Extended observation (up to 6+ hours or admission) for patients with severe initial presentation, requirement for >1 epinephrine dose, wide pulse pressure, unknown trigger, or cardiovascular comorbidities 1
- 1-hour observation may be reasonable for mild cases without risk factors 1
- Risk of biphasic reaction is 5% overall but increases to 17% in high-risk patients 1
Diagnostic Testing
- Obtain serum tryptase levels: first sample at 1 hour post-onset, second at 2-4 hours, and baseline >24 hours after reaction 2
Cardiac Arrest from Anaphylaxis
- Standard BLS/ACLS protocols with immediate epinephrine administration take priority 1
- No proven benefit from antihistamines, inhaled beta-agonists, or corticosteroids during cardiac arrest 1
- High-dose IV epinephrine (standard cardiac arrest dosing of 1 mg) may be required 3
Common Pitfalls to Avoid
- Delaying epinephrine is the most common fatal error—delay is associated with increased mortality and biphasic reactions 3, 6
- Using antihistamines first instead of epinephrine 1, 3
- Subcutaneous instead of intramuscular injection, which delays absorption 3, 7
- Placing patient upright, which can precipitate cardiovascular collapse 5
- Premature discharge without adequate observation period 1
- Failing to prescribe epinephrine autoinjector for home use and provide education 1, 3