Famotidine Dosing Calculation for a 69-lb Child
For a 69-lb (31 kg) child using a 40 mg/5 mL famotidine suspension, give 3.9 mL per dose (approximately 4 mL for practical administration).
Weight Conversion and Dose Calculation
- A 69-lb child weighs approximately 31.3 kg 1
- Standard pediatric famotidine dosing is 0.5 mg/kg per dose for children, based on pharmacokinetic studies showing this achieves therapeutic gastric acid suppression 2, 3
Step-by-Step Calculation
Dose in mg:
- 31 kg × 0.5 mg/kg = 15.5 mg per dose 3
Volume calculation with 40 mg/5 mL concentration:
- Set up proportion: 40 mg/5 mL = 15.5 mg/X mL
- X = (15.5 mg × 5 mL) ÷ 40 mg
- X = 3.875 mL per dose 2
Practical administration: Round to 3.9 mL or 4 mL per dose 4
Dosing Frequency
- Administer every 12 hours (twice daily) for children over 3 months of age 3
- This weight-based regimen (0.5 mg/kg/dose twice daily) maintains gastric pH above 4.0 for approximately 9 hours per dose in pediatric patients 5
Important Clinical Considerations
- Do not exceed adult doses: Maximum single dose should not exceed 40 mg, even if weight-based calculation suggests higher 6
- For this 31 kg child, the calculated 15.5 mg dose is well below the 40 mg adult maximum 2
- Bioavailability in children 11-15 years is similar to adults (approximately 40-45%), supporting weight-based dosing 2, 7
Common Pitfalls to Avoid
- Concentration confusion: Ensure you're using 40 mg/5 mL, not confusing with other concentrations 1
- Renal function: If the child has renal impairment (creatinine clearance <60 mL/min), reduce dose by 50% or more depending on severity 2, 8
- Tachyphylaxis: Prolonged IV use leads to decreased duration of efficacy, though this is less documented with oral therapy 5