What are the medications used to treat anaphylaxis?

Medications for Anaphylaxis Management

Epinephrine is the first-line and most critical medication for anaphylaxis treatment, and should be administered promptly via intramuscular injection in the mid-outer thigh at a dose of 0.01 mg/kg (maximum 0.5 mg) before any other interventions. 1

Primary Treatment: Epinephrine

Mechanism and Benefits

• Acts on both alpha and beta-adrenergic receptors 2:
  • α1 effects: Increases vasoconstriction, peripheral vascular resistance, and decreases mucosal edema
  • β1 effects: Increases inotropy (heart contractility) and chronotropy (heart rate)
  • β2 effects: Causes bronchodilation and decreases inflammatory mediator release from mast cells and basophils

Administration

• Route: Intramuscular injection in the lateral thigh (preferred site) 3, 1
• Dose: 0.01 mg/kg (maximum 0.5 mg) 1
• Autoinjector dosing:
  • 0.15 mg for patients 10-25 kg
  • 0.3 mg for patients >25 kg 1
• May repeat every 5-15 minutes if symptoms persist 3

Critical Importance

• Delayed epinephrine administration is associated with increased mortality and poor outcomes 3, 1
• No absolute contraindications to epinephrine in anaphylaxis, even with cardiac disease 1

Second-Line/Adjunctive Medications

Antihistamines

• H1 Antagonists (e.g., Diphenhydramine)

  • Dose: 1-2 mg/kg or 25-50 mg IV/IM/oral 3, 1
  • Role: Helps with cutaneous symptoms (urticaria, pruritus, flushing) only
  • Limitation: Does not treat respiratory or cardiovascular symptoms 3

• H2 Antagonists (e.g., Ranitidine)

  • Dose: 1 mg/kg or 50 mg IV 3, 1
  • Note: Combination of H1 and H2 antagonists is superior to H1 alone 3

Corticosteroids

• Methylprednisolone: 1-2 mg/kg/day IV every 6 hours 3, 1
• Prednisone: 0.5 mg/kg orally for less severe episodes 3
• Role: May help prevent protracted or biphasic reactions
• Limitation: No proven role in acute management; slow onset of action 3, 1

Bronchodilators

• Albuterol: 2.5-5 mg in 3 mL saline via nebulizer 3
• Role: For bronchospasm resistant to epinephrine 3

Vasopressors (for refractory hypotension)

• Dopamine: 400 mg in 500 mL D5W, administered at 2-20 μg/kg/min 3
• Requires continuous hemodynamic monitoring 3

Special Situations

• For patients on β-blockers with refractory symptoms:
  • Glucagon: 1-5 mg IV over 5 minutes, followed by infusion (5-15 μg/min) 3
  • Caution: May cause nausea and vomiting 3

Medication Sequence and Priorities

1. First: Epinephrine IM in lateral thigh
2. Second: Fluid resuscitation if hypotensive (20 mL/kg normal saline) 1
3. Third: Antihistamines for cutaneous symptoms
4. Fourth: Corticosteroids if history of severe reactions or asthma
5. Fifth: Bronchodilators if persistent bronchospasm
6. Sixth: Additional vasopressors if refractory hypotension

Common Pitfalls to Avoid

• Never delay epinephrine administration to administer antihistamines or corticosteroids first 3, 1
• Never use antihistamines alone as primary treatment for anaphylaxis 3
• Never administer epinephrine intravenously except in cardiac arrest or profound hypotension unresponsive to IM epinephrine and fluid resuscitation 3, 1
• Never discharge patients too early - observe for at least 4-6 hours after symptom resolution due to risk of biphasic reactions 1
• Never withhold epinephrine due to concerns about cardiac disease - benefits outweigh risks in anaphylaxis 1

Follow-up Medications

• Prescribe epinephrine autoinjectors upon discharge 1
• Consider 3-5 day course of oral antihistamines and corticosteroids for patients with severe reactions 1

Anaphylaxis is a potentially life-threatening condition requiring immediate recognition and treatment. While multiple medications play a role in management, epinephrine remains the cornerstone of therapy and should never be delayed or substituted.