What is the recommended dose of famotidine (H2 receptor antagonist) for pediatric patients experiencing an allergic reaction?

Famotidine Dosing for Pediatric Allergic Reactions

For pediatric patients experiencing anaphylaxis or allergic reactions, famotidine (an H2-receptor antagonist) should be administered at 1 mg/kg intravenously, diluted in D5W to a total volume of 20 mL and injected over 5 minutes, as an adjunctive therapy only after epinephrine has been given. 1

Critical First-Line Treatment Priority

Before considering famotidine, intramuscular epinephrine must be administered immediately at 0.01 mg/kg (maximum 0.3 mg in children) into the anterolateral thigh as the first-line treatment for anaphylaxis. 2, 3 Famotidine and other H2-receptor antagonists are second-line adjunctive therapies only and should never delay or replace epinephrine administration. 1

Famotidine Dosing Specifications

For Acute Allergic Reactions/Anaphylaxis:

• Dose: 1 mg/kg intravenously 1
• Preparation: Dilute in 5% dextrose (D5W) to a total volume of 20 mL 1
• Administration: Inject slowly over 5 minutes 1
• Alternative H2-antagonist: Ranitidine 1 mg/kg IV can be used similarly if famotidine is unavailable 1

Evidence Supporting H2-Antagonist Use:

The combination of an H1-antihistamine (diphenhydramine) plus an H2-antagonist (ranitidine or famotidine) is superior to diphenhydramine alone in managing anaphylaxis symptoms. 1 However, these agents have a much slower onset of action (≥1 hour) compared to epinephrine and do not relieve respiratory symptoms or shock. 2

Important Clinical Context

Timing and Sequence:

1. First: Administer epinephrine 0.01 mg/kg IM immediately 2, 3
2. Second: Establish IV access, provide oxygen, monitor vital signs 2
3. Third: Administer crystalloid fluid bolus (20-30 mL/kg for severe reactions) 2
4. Then: Consider famotidine 1 mg/kg IV as adjunctive therapy 1

Limitations of H2-Antagonists in Acute Allergic Reactions:

• Slow onset: Takes approximately 1 hour to achieve therapeutic effect 2
• Limited scope: Primarily helpful for cutaneous symptoms and potentially preventing prolonged reactions 1
• Not life-saving: Does not address airway compromise, bronchospasm, or cardiovascular collapse 2

Alternative Dosing for Non-Emergency Indications

For gastroesophageal reflux disease (not allergic reactions), the pediatric dosing differs significantly:

• Oral dosing: 1 mg/kg/day divided in 2 doses 1
• IV dosing for GERD: 0.4-0.8 mg/kg per dose 4

This dosing is not applicable to acute allergic reactions and should not be confused with the anaphylaxis dosing of 1 mg/kg IV as a single dose. 1

Critical Pitfalls to Avoid

• Never substitute famotidine or any antihistamine for epinephrine as first-line treatment—this is associated with fatalities 2, 3
• Do not delay epinephrine administration while preparing IV famotidine 2
• Recognize that famotidine alone will not reverse bronchospasm, laryngeal edema, or hypotension 2
• Remember that patients with severe asthma or those on beta-blockers are at higher risk for fatal anaphylaxis and may require additional interventions beyond standard dosing 2

Post-Treatment Monitoring

After administering famotidine as adjunctive therapy:

• Observe patients for minimum 6 hours in a monitored setting 2, 3
• Watch for biphasic reactions, which can occur despite initial treatment 1
• Prescribe epinephrine autoinjector before discharge 2
• Arrange allergist referral for trigger identification 2