What is the drug of choice for treating anaphylactic shock?

Drug of Choice for Anaphylactic Shock

Epinephrine is the drug of choice for anaphylactic shock and should be administered immediately as the first-line treatment to prevent mortality. 1, 2, 3

Initial Administration

• First-line approach: Intramuscular (IM) epinephrine in the anterolateral aspect of the thigh
  • Adult dose: 0.3-0.5 mg (0.3-0.5 mL of 1:1000 solution) 2, 3
  • Children ≥30 kg: 0.3-0.5 mg (0.3-0.5 mL of 1:1000 solution) 3
  • Children <30 kg: 0.01 mg/kg (0.01 mL/kg), maximum 0.3 mg 3
• Repeat every 5-10 minutes as necessary if symptoms persist 3

IV Epinephrine for Refractory Cases

• Only for patients with profound hypotension or cardiac arrest who have failed to respond to IM epinephrine and IV fluid resuscitation 1, 2
• IV bolus dose: 0.05-0.1 mg (5-10% of cardiac arrest dose) administered slowly 2
• IV infusion: For persistent shock, prepare a 1:100,000 solution (1 mg in 100 mL saline) and administer at 5-15 μg/min, titrated to response 1, 2
• Warning: IV bolus epinephrine carries significantly higher risk of cardiovascular complications and overdose compared to IM administration (odds ratio 8.7) 4

Concurrent Management

1. Aggressive fluid resuscitation with isotonic crystalloids (normal saline) 2

   • Administer repeated boluses to maintain systolic BP >90 mmHg
   • Vasogenic shock may require large volumes due to increased capillary permeability

2. Second-line medications (never use in place of epinephrine):

   • Diphenhydramine: 1-2 mg/kg or 25-50 mg parenterally 1, 2
   • Ranitidine: 1 mg/kg or 50 mg IV (adults) 1, 2
   • Note: Combination of H1 and H2 blockers is superior to H1 blockers alone 1

3. For bronchospasm resistant to epinephrine:

   • Nebulized albuterol: 2.5-5 mg in 3 mL saline, repeat as necessary 1, 2

4. For refractory hypotension:

   • Dopamine: 400 mg in 500 mL D5W at 2-20 μg/kg/min, titrated to maintain systolic BP >90 mmHg 1, 2
   • Continuous hemodynamic monitoring is essential

Special Considerations

• Patients on β-blockers: Consider glucagon 1-5 mg IV over 5 minutes, followed by infusion (5-15 μg/min) 1, 2
• Corticosteroids: Not helpful acutely but may prevent recurrent or protracted anaphylaxis 1, 2
  • IV methylprednisolone: 1-2 mg/kg/day every 6 hours
  • Oral prednisone: 0.5 mg/kg for less critical episodes

Pitfalls to Avoid

1. Delaying epinephrine administration - failure to inject promptly contributes to anaphylaxis fatalities 5
2. Using antihistamines as first-line treatment - these should never replace epinephrine 2
3. Injecting epinephrine into buttocks, digits, hands, or feet - can cause tissue damage 3
4. Using IV bolus epinephrine unnecessarily - associated with 13.3% risk of overdose compared to 0% with IM route 4
5. Underestimating the need for prolonged observation - biphasic reactions can occur

Monitoring and Disposition

• Close hemodynamic monitoring is essential as cardiovascular and respiratory status can change rapidly 2
• Immediately assess for signs of airway compromise (hoarseness, stridor, lingual edema) 2
• Consider transportation to emergency department or intensive care facility for continued observation 1