What is the first-line treatment for anaphylactic shock in infants?

First-Line Treatment of Anaphylactic Shock in Infants

Epinephrine administered intramuscularly (IM) into the anterolateral thigh at a dose of 0.01 mg/kg of a 1:1000 (1 mg/mL) solution is the first-line treatment for anaphylactic shock in infants. 1

Dosing and Administration

Primary Treatment

• Route: Intramuscular (IM) injection in the mid-outer aspect of the thigh
• Concentration: 1:1000 (1 mg/mL) solution
• Dose: 0.01 mg/kg (maximum 0.3 mg) 1
• Timing: Administer immediately upon recognition of anaphylaxis
• Repeat dosing: May repeat every 5-20 minutes if symptoms persist 1

Epinephrine Autoinjectors

• For infants weighing >7.5 kg, a 0.15 mg autoinjector may be used 1
• For smaller infants (<7.5 kg), a 0.1 mg autoinjector is ideal when available 1
• The practical advantage of using autoinjectors (speed and precision) may outweigh concerns about slight overdosing in smaller infants 1

Recognition of Anaphylaxis in Infants

Anaphylaxis in infants may present with symptoms affecting multiple organ systems:

• Skin: Itching, redness, hives, swelling
• Respiratory: Hoarseness, throat tightness, stridor, cough, difficulty breathing, wheezing
• Cardiovascular: Tachycardia, weak pulse, hypotension, dizziness, collapse
• Gastrointestinal: Nausea, vomiting, crampy abdominal pain, diarrhea
• Behavioral changes: Irritability, lethargy 1

Treatment Algorithm

1. Recognize anaphylaxis - Assess airway, breathing, circulation, and skin
2. Administer epinephrine IM - 0.01 mg/kg of 1:1000 solution in anterolateral thigh
3. Position patient appropriately - Lay flat with legs elevated (if no respiratory distress)
4. Call emergency services - Transport to emergency department
5. Consider second dose - If no improvement in 5-15 minutes
6. Adjunctive therapy (after epinephrine):
   • Diphenhydramine 1-2 mg/kg IV/IM (maximum 50 mg) 1, 2
   • Ranitidine 1 mg/kg IV (if available) 1
   • Supplemental oxygen if needed
   • IV fluids for hypotension

Important Considerations

• Never delay epinephrine administration - It is the only medication proven to reduce mortality in anaphylaxis
• Antihistamines are second-line therapy - They should never be used alone or before epinephrine 1, 2
• H1 and H2 blockers in combination are superior to H1 blockers alone, but still secondary to epinephrine 1
• Glucocorticoids may be considered for preventing biphasic or protracted reactions, but have no immediate benefit 1

Common Pitfalls to Avoid

1. Delaying epinephrine administration - This is the most common error in managing anaphylaxis
2. Using subcutaneous instead of IM route - IM provides faster and more reliable absorption 3
3. Using inhaled epinephrine - Studies show this is ineffective as a substitute for IM epinephrine 4
4. Relying on antihistamines alone - These medications do not treat cardiovascular or respiratory symptoms effectively
5. Failure to recognize anaphylaxis in infants - Symptoms may be subtle or atypical 5
6. Underestimating severity - Infants can deteriorate rapidly; early intervention is critical

Monitoring and Follow-up

• Observe for at least 4-6 hours after initial symptoms resolve
• Monitor for biphasic reactions (recurrence of symptoms after initial resolution)
• Arrange consultation with an allergist-immunologist
• Provide caregivers with an epinephrine autoinjector and proper training before discharge

Remember that epinephrine is life-saving in anaphylaxis, and the benefits of prompt administration far outweigh the risks of transient side effects such as pallor, tremor, anxiety, and palpitations 1.