What is the recommended treatment for anaphylaxis?

Anaphylaxis Treatment

Intramuscular epinephrine (0.3-0.5 mg of 1:1000 solution) injected into the anterolateral thigh is the immediate first-line treatment for anaphylaxis and should be administered without delay at the first signs of a systemic allergic reaction. 1, 2

Immediate Management Algorithm

Step 1: Epinephrine Administration (DO THIS FIRST)

• Administer intramuscular epinephrine immediately into the anterolateral thigh (vastus lateralis) at the first sign of anaphylaxis—this route achieves faster and higher plasma levels than subcutaneous or deltoid injection 1, 2, 3
• Adult dosing: 0.3-0.5 mg (or 0.01 mg/kg) of 1:1000 concentration (1 mg/mL), maximum single dose 0.5 mg 1, 3
• Pediatric dosing: 0.01 mg/kg of 1:1000 solution, maximum 0.3 mg in children 1, 2
• Autoinjector doses: 0.15 mg for children 10-25 kg; 0.3 mg for patients ≥25 kg; consider 0.5 mg for patients ≥45 kg 2, 4
• Repeat every 5-15 minutes as needed if symptoms persist or recur 1
• No absolute contraindications exist for epinephrine in anaphylaxis, including in elderly patients, those with cardiac disease, or other comorbidities 1, 2

Step 2: Positioning and Supportive Care

• Position patient supine with legs elevated (unless respiratory distress prevents this) 2
• In pregnant women, perform left uterine displacement to avoid aortocaval compression 2
• Administer supplemental oxygen 2
• Establish intravenous access 2

Step 3: Fluid Resuscitation

• Grade II reactions: Initial bolus of 0.5 L crystalloids 2
• Grade III reactions: Initial bolus of 1 L crystalloids 2
• Repeat boluses as needed up to 20-30 mL/kg based on clinical response to combat vasodilation and capillary leak 2

Refractory Anaphylaxis Management

When Initial IM Epinephrine Fails

• IV epinephrine bolus: Consider when IV access is established—dose 0.05-0.1 mg (50-100 mcg) of 1:10,000 concentration for shock 1
• IV epinephrine infusion: 5-15 mcg/min (or 0.05-0.1 mcg/kg/min) for persistent symptoms after multiple IM doses 1, 2
• Alternative vasopressors: Norepinephrine, vasopressin, phenylephrine, or metaraminol may be used for persistent hypotension 2
• Glucagon: 1-2 mg IV for patients on beta-blockers who may be resistant to epinephrine 2

Cardiac Arrest from Anaphylaxis

• Standard BLS/ACLS takes priority with immediate epinephrine administration 1
• Airway management is critical—be prepared for emergency cricothyroidotomy or tracheostomy if severe oropharyngeal/laryngeal edema develops 1

Secondary Treatments (ONLY After Epinephrine)

What NOT to Give First

• Antihistamines, corticosteroids, and bronchodilators are NOT first-line treatments and should only be considered after epinephrine and stabilization 1
• H1 antihistamines (diphenhydramine 25-50 mg IV or chlorphenamine) may treat cutaneous symptoms for comfort but do NOT address life-threatening manifestations 1, 2
• H2 antihistamines (ranitidine 50 mg IV) have no high-quality evidence supporting efficacy in anaphylaxis 1
• Corticosteroids have no role in acute anaphylaxis due to slow onset of action and do NOT prevent biphasic reactions 1

Observation and Monitoring

Duration of Observation

• Minimum 6 hours of monitored observation for all patients until stable and symptoms fully resolved 1, 2
• Extended observation or ICU admission for patients with severe anaphylaxis (Grade III-IV), those requiring >1 dose of epinephrine, or those with risk factors for biphasic reactions 1, 2
• Discharge after 1 hour may be reasonable only for patients without severe features and low risk 1

Biphasic Anaphylaxis Risk Factors

• Severe initial reaction requiring multiple epinephrine doses (odds ratio 4.82) 1
• Wide pulse pressure, unknown trigger, cutaneous symptoms, drug triggers in children 1
• Occurs in approximately 10% of cases, with mean onset at 11 hours (up to 72 hours possible) 1

Tryptase Sampling

• First sample: 1 hour after reaction onset 2
• Second sample: 2-4 hours after onset 2
• Baseline sample: At least 24 hours post-reaction for comparison 2

Discharge Requirements

Mandatory Prescriptions

• Two epinephrine autoinjectors (0.15 mg for 10-25 kg; 0.3 mg for ≥25 kg) 2
• Written personalized anaphylaxis emergency action plan including symptoms, instructions, and known triggers 2

Critical Patient Education

• Inject epinephrine FIRST at earliest sign of anaphylaxis—delayed administration is directly associated with fatalities 2, 5
• Always seek emergency care after using epinephrine even if symptoms improve, due to biphasic reaction risk 2
• Monitor autoinjector expiration dates as epinephrine degrades over time 2
• Refer to allergist for trigger identification and ongoing risk assessment 1, 2

Common Pitfalls to Avoid

• Never delay epinephrine for antihistamines or corticosteroids—this is associated with increased mortality 1, 2, 5
• Never administer epinephrine subcutaneously or in the deltoid—IM thigh injection is superior 2, 5
• Never place patient upright—this can precipitate cardiovascular collapse; keep supine with legs elevated 6
• Never discharge without two autoinjectors and written action plan—this is a critical safety requirement 2
• Never assume antihistamines or steroids prevent biphasic reactions—they do not, and may actually increase risk in children 1