What is the appropriate dose of Pepcid (famotidine) for a 50-pound patient experiencing an allergic reaction?

Famotidine Dosing for a 50-Pound Child with Allergic Reaction

For a 50-pound (22.7 kg) child experiencing an allergic reaction, the appropriate dose of famotidine is 0.5 mg/kg/dose, which equals approximately 11 mg, administered orally every 12 hours.

Dosing Calculation and Rationale

The FDA-approved famotidine dosing is based on weight and renal function. For this specific case:

• A 50-pound child weighs approximately 22.7 kg
• The recommended pediatric dosing for famotidine is 0.5 mg/kg/dose given twice daily
• Therefore: 22.7 kg × 0.5 mg/kg = 11.35 mg per dose

Administration Considerations

• For children under 40 kg, the FDA label specifically notes that the 20 mg tablet strength exceeds the recommended dose 1
• Options for administration include:
  • Oral suspension (preferred for accurate dosing)
  • Lower-dose tablet formulation that can be split
  • Timing: Every 12 hours (twice daily)

Role in Allergic Reaction Management

It's critical to understand that famotidine is NOT first-line therapy for allergic reactions:

1. Epinephrine is the primary treatment for anaphylaxis and severe allergic reactions 2

   • For a 50-pound child, epinephrine dosing would be 0.01 mg/kg (0.15 mg autoinjector is appropriate)
   • The 0.15 mg epinephrine autoinjector is recommended for children weighing 7.5-25 kg 2

2. Famotidine (H2 antagonist) serves as adjunctive therapy alongside:

   • H1 antihistamines (diphenhydramine 1-2 mg/kg, maximum 50 mg) 3
   • The combination of H1 and H2 antagonists provides enhanced efficacy 3

Treatment Algorithm for Allergic Reactions

Mild-Moderate Allergic Reaction (hives, pruritus without respiratory/cardiovascular involvement):

1. Diphenhydramine 1-2 mg/kg (max 50 mg) orally every 6 hours 3
2. Famotidine 0.5 mg/kg (11 mg for this child) orally every 12 hours 1
3. Monitor for progression of symptoms

Severe Allergic Reaction/Anaphylaxis:

1. Epinephrine 0.01 mg/kg IM (0.15 mg autoinjector for this 50-pound child) 2
2. Call emergency services
3. Diphenhydramine 1-2 mg/kg IV/IM/PO (max 50 mg) 3
4. Famotidine 0.5 mg/kg IV/PO (11 mg for this child) 1
5. Consider corticosteroids for preventing biphasic reactions 2

Important Clinical Considerations

• Famotidine has a rapid onset of action (within 1 hour orally) with peak effect at 1-3 hours 4
• Duration of action is 10-12 hours, supporting twice-daily dosing 4
• Famotidine is primarily eliminated through the kidneys (70%), so dose adjustment is needed in renal impairment 1
• Famotidine has minimal drug interactions compared to other H2 antagonists 5
• Anaphylactic reactions to H2 antagonists themselves are rare but have been reported 6

Practical Administration Tips

• For a 50-pound child, use an oral suspension formulation for most accurate dosing
• If using tablets, a lower-dose formulation that can be split would be needed
• Famotidine can be given with or without food
• Continue for 2-3 days after acute allergic symptoms resolve

Remember that famotidine is only an adjunctive treatment for allergic reactions. Epinephrine remains the definitive life-saving treatment for anaphylaxis, with antihistamines providing symptomatic relief but not replacing epinephrine in severe reactions.