Famotidine Dosing for Pediatric Patients
For infants and children requiring famotidine, use 0.5 mg/kg per dose with age-adjusted frequency: once daily for infants <3 months and twice daily (every 12 hours) for infants and children ≥3 months of age. 1, 2
Dosing Recommendations by Age
Infants <3 Months
- Dose: 0.5 mg/kg once daily 2
- Rationale: Younger infants have decreased plasma and renal clearance of famotidine due to immature renal function, requiring less frequent dosing to prevent accumulation 2
Infants and Children ≥3 Months
- Dose: 0.5 mg/kg every 12 hours (twice daily) 1, 2
- Rationale: Pharmacokinetic parameters in infants >3 months are similar to older children and adults, allowing for standard twice-daily dosing 2
Concentration Selection: 20 mg/5 mL vs 40 mg/5 mL
Either concentration (20 mg/5 mL or 40 mg/5 mL) can be used; the choice depends on the calculated dose volume for ease of administration. The 40 mg/5 mL concentration allows for smaller volumes when higher doses are needed, while 20 mg/5 mL provides better precision for very small doses in younger/lighter infants. 3
Practical Calculation Example
- For a 10 kg child ≥3 months: 0.5 mg/kg × 10 kg = 5 mg per dose
- Using 20 mg/5 mL: 1.25 mL per dose
- Using 40 mg/5 mL: 0.625 mL per dose
- For a 5 kg infant <3 months: 0.5 mg/kg × 5 kg = 2.5 mg once daily
- Using 20 mg/5 mL: 0.625 mL once daily
- Using 40 mg/5 mL: 0.3125 mL once daily
Route of Administration
- Oral route is preferred when the child can tolerate oral medications 1, 2
- Intravenous route can be used at 0.25 mg/kg per dose (half the oral dose) due to 100% bioavailability, with the same age-adjusted frequency 2
- Bioavailability of oral famotidine in infants is similar to adult values, supporting oral administration when feasible 2
Efficacy and Safety Considerations
- Effective window: Famotidine is effective 1.5-6 hours after oral administration 3
- pH elevation: All doses (0.15-0.6 mg/kg) significantly increase gastric pH above 2.5 in 75-94% of patients 3
- Common adverse effects: Agitation/irritability (including head-rubbing), somnolence, anorexia, and headache may occur in infants 1
- No accumulation: Multiple dosing does not lead to drug accumulation when age-appropriate frequencies are used 2
Critical Pitfalls to Avoid
- Do not use adult weight-based dosing (mg/kg) without age adjustment of frequency in infants <3 months, as this will lead to drug accumulation and potential toxicity due to immature renal function 2, 4
- Do not extrapolate dosing from older children to neonates without considering maturational differences in drug elimination 4
- Monitor for paradoxical agitation in infants, as this is a recognized adverse effect that may be mistaken for worsening reflux symptoms 1
Dose Individualization
While 0.5 mg/kg is the standard starting dose, some infants may require up to 1.0 mg/kg per dose for optimal symptom control, particularly for regurgitation frequency and volume 1. However, start with 0.5 mg/kg and titrate upward only if inadequate response after appropriate trial duration. 1