How should a 15‑month‑old infant be treated for an allergic reaction?

Treatment of Allergic Reactions in a 15-Month-Old Infant

Immediately administer intramuscular epinephrine 0.01 mg/kg (0.15 mg autoinjector for children 10-25 kg) into the lateral thigh if the allergic reaction involves any respiratory symptoms, tongue/lip swelling, cardiovascular symptoms, or rapidly spreading hives—this is the only first-line treatment that reduces mortality and must not be delayed. 1, 2

Immediate Assessment and Recognition

When evaluating a 15-month-old with an allergic reaction, rapidly assess for signs of anaphylaxis beyond isolated hives:

Respiratory symptoms that mandate immediate epinephrine include: 2

• Wheezing, stridor, or dyspnea
• Throat tightness or difficulty swallowing
• Persistent cough

Cardiovascular symptoms requiring epinephrine: 2

• Hypotension, tachycardia, or syncope
• Dizziness or pallor

Other concerning features in infants that are often missed: 3, 4

• Drooling (may indicate oropharyngeal swelling)
• Persistent vomiting or diarrhea
• Excessive scratching or irritability
• Drowsiness or lethargy

Critical pitfall: Infants are nonverbal and symptoms can be subtle or mistaken for normal developmental findings—do not wait for classic symptoms to develop before treating. 3, 4

Treatment Algorithm

For Anaphylaxis (Multi-System Involvement or Severe Symptoms)

Step 1: Epinephrine Administration 1, 2

• Dose: 0.01 mg/kg intramuscular (0.15 mg autoinjector for 10-25 kg; 0.30 mg for ≥25 kg)
• Route: Intramuscular into lateral thigh (vastus lateralis)—this is the ONLY acceptable route
• Timing: Immediately upon recognition—do not delay for IV access or other interventions
• Repeat: Every 5-15 minutes if symptoms persist 1

Step 2: Positioning and Monitoring 2

• Position supine with legs elevated (unless respiratory distress present)
• Monitor vital signs every 5 minutes
• Call for emergency transport

Step 3: Adjunctive Treatments (AFTER epinephrine) 1

• Albuterol: 4-8 puffs via MDI or 1.5 mL nebulized for bronchospasm
• Diphenhydramine: 1-2 mg/kg (maximum 50 mg) for H1 blockade
• Supplemental oxygen as needed
• IV fluids for hypotension

For Isolated Hives Without Systemic Symptoms

If only skin involvement (isolated hives) with NO respiratory, cardiovascular, or GI symptoms: 5

• H1 antihistamine (cetirizine 0.25 mg/kg once daily or loratadine weight-based)
• Monitor closely for 30-60 minutes for progression
• Prescribe epinephrine autoinjector even if not used—isolated hives can rapidly progress 2

Critical warning: Never rely on antihistamines alone if there is ANY doubt about progression—they have dangerously slow onset and are ineffective for anaphylaxis. 2

Post-Treatment Management

All patients who receive epinephrine must: 1

• Be transported to emergency facility by ambulance
• Undergo observation for 4-6 hours minimum (longer if severe symptoms or history of asthma)
• Remain monitored for biphasic reactions (occur in 1-20% of cases, typically around 8 hours but up to 72 hours later) 1, 6

Discharge Requirements

Every child with an allergic reaction (even if mild) must be discharged with: 1, 7

• Two epinephrine autoinjectors (0.15 mg for this age/weight)
• Written anaphylaxis emergency action plan
• Training for caregivers on recognizing symptoms and administering epinephrine
• Referral to allergist for trigger identification and long-term management
• Antihistamines for mild reactions

Education must include: 7

• Food avoidance strategies and label reading
• Recognition that even small amounts of allergen can trigger anaphylaxis
• Instructions that epinephrine must be available at ALL times
• Notification of daycare/school personnel with written action plan
• Understanding that any food allergy can be progressively more severe on next exposure 7

Special Considerations for Infants

Dosing challenge: Current autoinjector doses (0.15 mg) may be too high for infants <15 kg, but the benefit of immediate treatment outweighs theoretical overdose risk. 1, 8

Common triggers at this age: 3, 9

• Egg, cow's milk, and peanuts are most common
• First reactions are often the first diagnosis—making history difficult

High-risk features requiring extra vigilance: 1, 6

• Coexisting asthma
• Previous anaphylactic reaction
• Peanut or tree nut allergy

What NOT to Do

• Never delay epinephrine waiting for symptoms to worsen or for IV access 2
• Never use antihistamines as sole treatment for anything beyond isolated hives 2
• Never assume isolated hives will remain isolated—prescribe epinephrine regardless 2
• Never discharge without epinephrine autoinjector and comprehensive education 1