Anaphylaxis / Allergic Reaction

Adult · Routine allergic reaction

Urticaria · pruritus · mild angioedema (no airway / CV / GI)

Management
  • Remove trigger if identifiable (stop infusion, remove stinger).
  • Assess ABCs and reassess for any anaphylaxis criteria (airway, breathing, circulation, GI).
  • Vitals on arrival and q15–30 min while symptomatic.
  • PO/IV antihistamines and steroid are first-line — see doses below.
  • Escalate to anaphylaxis pathway immediately if airway swelling, wheeze, hypotension, syncope, or vomiting/diarrhea develop.
First-line adult dosing
  • () 25–50 mg PO/IV/IM — H1 blocker.
  • () 10 mg PO — non-sedating H1 alternative.
  • () 20 mg PO/IV — H2 blocker.
  • () 125 mg IV — corticosteroid (or 40–60 mg PO × 5 days).
  • 2.5 mg nebulized — for wheezing/bronchospasm; repeat PRN.

Disposition: observe until symptoms improving; discharge with 3-day H1 + H2 + steroid course and EpiPen if any concerning features.

Adult · Anaphylaxis

Airway / breathing / circulation / GI involvement — give IM epi NOW

First-line · IM Epinephrine (adult)
  • 0.3–0.5 mg IM (0.3–0.5 mL of 1 mg/mL · 1:1,000).
  • Site: mid-anterolateral thigh (vastus lateralis), 90° to skin.
  • Auto-injector: 0.3 mg (≥ 30 kg).
  • Repeat q5–15 min PRN — most patients need ≥ 2 doses; alternate thighs.
  • Never use 0.1 mg/mL (1:10,000) for IM dosing — that is the IV/code concentration.
  • Refractory: start infusion 0.05–0.5 mcg/kg/min and consider 1–5 mg IV if on β-blocker.
Management
  • Remove trigger; call for help and code cart.
  • Position: supine with legs elevated; semi-recumbent if dyspneic; recovery if vomiting. Avoid sudden upright posture.
  • High-flow O₂ via NRB; prepare for early intubation if stridor / progressive angioedema.
  • 2× large-bore IV; NS or LR 1–2 L bolus for hypotension (up to 30 mL/kg).
  • Continuous monitoring: SpO₂, ECG, NIBP q5 min.
  • Adjuncts after epi (do not delay epi):
    • () 25–50 mg IV/IM — H1 blocker.
    • () 20 mg IV — H2 blocker.
    • () 125 mg IV — corticosteroid.
    • 2.5–5 mg nebulized — for bronchospasm; repeat PRN.
  • Reassess q5 min; repeat IM epi q5–15 min PRN.
Post-epinephrine monitoring · vital-sign checklist

Biphasic reactions can occur up to 72 h after initial event — counsel return precautions regardless of tier.

Tier 1 · Standard observation
4–6 hours
Trigger criteria
  • Single IM epi dose with full symptom resolution
  • Normotensive throughout, no airway involvement
  • No asthma, no β-blocker, no prior biphasic reaction
Vital-sign reassessment
  • HR, BP, RR, SpO₂ q5 min × first 30 min after epi
  • Then q15 min × 2 h
  • Then q30 min × remaining observation
  • Lung auscultation + skin/airway exam q1 h
Tier 2 · Extended observation
8–12 hours
Trigger criteria
  • ≥ 2 IM epi doses required
  • Initial hypotension (SBP < 90) or syncope
  • Airway/laryngeal involvement (hoarseness, stridor, tongue swelling)
  • Active bronchospasm or known asthma
  • Severe initial reaction or unknown trigger
Vital-sign reassessment
  • Continuous SpO₂ + cardiac telemetry
  • BP q5 min × 30 min, then q15 min × 4 h, then q30 min
  • RR + work of breathing q15 min × 4 h
  • Lung + airway exam q1 h
Tier 3 · Admit (monitored bed / ICU)
≥ 12–24 hours
Trigger criteria
  • Refractory symptoms or epi infusion required
  • Intubation, persistent stridor, or angioedema progressing
  • Hemodynamic instability after fluid resuscitation
  • On β-blocker / ACE-inhibitor (blunted response)
  • Prior biphasic anaphylaxis or any persistent symptoms at 6 h
  • Unreliable follow-up or unable to access epi at home
Vital-sign reassessment
  • Continuous telemetry, SpO₂, end-tidal CO₂ if intubated
  • BP q5–15 min until stable × 4 h, then q1 h
  • Hourly airway + neuro + perfusion checks × 12 h
  • Recheck labs (ABG, lactate) if shock or refractory
Discharge bundle (any tier)
  • 2× epinephrine auto-injectors prescribed + technique demonstrated
  • 3-day H1 (cetirizine 10 mg PO daily) + H2 (famotidine 20 mg PO BID) + prednisone 40–60 mg PO daily
  • Written anaphylaxis action plan reviewed with patient/family
  • Allergy / immunology referral arranged; MedicAlert recommended
  • Return precautions: airway sx, recurrent reaction, syncope → 911
Note: IV bolus dosing is no longer recommended to treat anaphylaxis

Epinephrine Infusion

  • 4 mg/250 mL = 16 mcg/mL
  • 8 mg/250 mL = 32 mcg/mL
  • 16 mg/250 mL = 64 mcg/mL
  • Weight-Based Infusion Range: 0.05-1 mcg/kg/min
4 mg / 250 mL 0.05 mL/min
Range start (0.05 mcg/kg/min × 16 kg)0 mL
8 mg / 250 mL 0.03 mL/min
Range start (0.05 mcg/kg/min × 16 kg)0 mL
16 mg / 250 mL 0.01 mL/min
Range start (0.05 mcg/kg/min × 16 kg)0 mL
Fluid bolus (refractory shock)
20 mL/kg
— mL

Repeat × 2-3 PRN