What is the treatment for anaphylaxis in infants?

Treatment of Anaphylaxis in Infants

Immediately administer intramuscular epinephrine 0.01 mg/kg (1:1000 solution) into the mid-outer thigh as soon as anaphylaxis is recognized—this is the only first-line treatment and must never be delayed or substituted with antihistamines or other medications. 1, 2

Immediate Epinephrine Administration

Dosing and Route

• Inject epinephrine 0.01 mg/kg of 1:1000 solution intramuscularly into the anterolateral thigh (vastus lateralis muscle) immediately upon recognition of anaphylaxis 3, 1, 4
• The intramuscular route in the lateral thigh achieves peak plasma concentrations in 8 ± 2 minutes, compared to 34 ± 14 minutes with subcutaneous injection, making it vastly superior for emergency treatment 3, 5
• Repeat epinephrine every 5-15 minutes as needed if symptoms persist or recur 3, 2

Autoinjector Dosing for Infants

• For infants weighing >7.5 kg but <15 kg, prescribe the 0.15 mg epinephrine autoinjector despite it being a higher dose than the calculated 0.01 mg/kg 3, 1
• For infants <7.5 kg, the 0.15 mg autoinjector is still preferable to ampule/syringe methods, which carry a 40-fold variation in dosing accuracy and significant delays that outweigh theoretical overdosing concerns 2, 6
• Drawing up doses from ampules can take 3-4 minutes and often results in inaccurate or completely missed doses, making autoinjectors the safer choice even if the dose is higher than calculated 3
• The adverse effects of a 0.15 mg dose in small infants (transient pallor, tremor, anxiety, palpitations) are mild and transient compared to the risk of death from untreated anaphylaxis 3, 6

Supportive Measures (After Epinephrine)

Positioning and Monitoring

• Position the infant supine with legs elevated (unless respiratory distress is present) 7
• Establish IV access, provide supplemental oxygen, and continuously monitor vital signs 2, 7

Fluid Resuscitation

• Administer crystalloid fluid bolus: 500 mL for moderate reactions, 1 L for severe reactions, escalating to 20-30 mL/kg for refractory cases 2, 7
• Fluid resuscitation is critical to combat vasodilation and capillary leak 7

Adjunctive Treatments (Never Before Epinephrine)

Antihistamines

• H1 antihistamines (diphenhydramine) are adjunctive only for cutaneous symptoms and should never be administered before or instead of epinephrine 3, 2, 7
• Antihistamines have slow onset (≥1 hour) and do not relieve respiratory symptoms or shock 3
• If used, administer diphenhydramine 1-2 mg/kg (maximum 50 mg) only after epinephrine has been given 7

Bronchodilators

• Inhaled albuterol may provide adjunctive therapy for wheezing in infants with preexisting asthma but does not replace epinephrine and does not treat upper airway edema or shock 3

Corticosteroids

• Consider systemic glucocorticosteroids for infants with severe/prolonged reactions to potentially prevent biphasic reactions, but these are not first-line treatment 2

Management of Refractory Anaphylaxis

When Initial Epinephrine Fails

• If inadequate response after 10 minutes, double the epinephrine bolus dose 2
• Consider IV epinephrine only for cardiac arrest or profound hypotension unresponsive to multiple IM doses and aggressive fluid resuscitation 2, 8
• IV epinephrine dosing: 0.01 mg/kg (0.1 mL/kg of 1:10,000 solution; maximum 0.3 mg) given slowly over several minutes with continuous hemodynamic monitoring 2
• Start epinephrine infusion (0.05-0.1 μg/kg/min) when more than three boluses have been administered 2, 7

Alternative Vasopressors

• For persistent hypotension despite epinephrine, add norepinephrine infusion (0.05-0.5 μg/kg/min) 2
• Consider vasopressin 1-2 IU bolus with or without infusion (2 units/h) for refractory hypotension 2

Post-Anaphylaxis Care

Observation Period

• All infants who receive epinephrine must be transported to an emergency facility for observation of 4-6 hours minimum or until stable and symptoms are regressing 1, 2, 7
• Biphasic reactions (symptom recurrence hours later) can occur, necessitating prolonged observation 7, 9

Tryptase Sampling

• Obtain mast cell tryptase samples: first at 1 hour after reaction onset, second at 2-4 hours, and baseline at least 24 hours post-reaction 2, 7

Discharge Requirements

• Prescribe two epinephrine autoinjectors (0.15 mg for infants >7.5 kg) before discharge 3, 1, 7
• Provide a written, personalized anaphylaxis emergency action plan that includes symptom recognition, clear instructions, and known triggers 1, 7
• Train caregivers on autoinjector use and anaphylaxis recognition 1, 2
• Arrange allergist referral for trigger identification and ongoing management 2, 7

Critical Pitfalls to Avoid

• Delayed epinephrine administration is directly associated with anaphylaxis fatalities—never substitute antihistamines, corticosteroids, or bronchodilators as first-line treatment 3, 2, 7, 6
• Do not use IV epinephrine in non-arrest situations without appropriate monitoring, as it carries significant risk of dilution and dosing errors 3, 2
• Never prescribe ampule/syringe/needle methods for home use due to unacceptable dosing errors and delays 3, 2
• There are no absolute contraindications to epinephrine use in anaphylaxis—the benefits always outweigh the risks 3, 7
• Avoid premature discharge without adequate observation for biphasic reactions 2, 7