What is the correct dose of famotidine oral suspension (40 mg/5 mL) for an 8‑month‑old infant weighing 5 kg?

Famotidine Dosing for an 8-Month-Old Infant Weighing 5 kg

For a 5 kg, 8-month-old infant, the appropriate dose of famotidine oral suspension (40 mg/5 mL) is 2.5 mg twice daily, which equals 0.3 mL of the 40 mg/5 mL suspension given twice daily.

Weight-Based Dosing Calculation

• The established pediatric dose of famotidine is 0.5 mg/kg twice daily (maximum 40 mg/day total) 1, 2
• For a 5 kg infant: 5 kg × 0.5 mg/kg = 2.5 mg per dose
• Given twice daily (every 12 hours), this provides a total daily dose of 5 mg/day 1

Suspension Volume Calculation

• Your famotidine suspension concentration is 40 mg per 5 mL, which equals 8 mg/mL
• To deliver 2.5 mg per dose: 2.5 mg ÷ 8 mg/mL = 0.3125 mL (round to 0.3 mL for practical administration)
• Administer 0.3 mL twice daily (morning and evening, approximately 12 hours apart)

Evidence Supporting This Dosing

• Multiple pharmacokinetic studies in children demonstrate that 0.5 mg/kg every 8-12 hours effectively suppresses gastric acid secretion and is well-tolerated 1, 2
• The twice-daily regimen (every 12 hours) maintains intragastric pH elevation and has proven efficacy in healing gastroduodenal ulcers in pediatric patients within 8 weeks 1
• Bioavailability of oral famotidine is approximately 50%, with peak plasma concentrations reached in 1-3 hours and duration of action lasting 10-12 hours 3

Administration Instructions

• Use a 1 mL oral syringe for accurate measurement of the 0.3 mL dose
• Administer without regard to meals, though giving with food may improve tolerability 3
• Maintain consistent timing (e.g., 8 AM and 8 PM) to ensure steady acid suppression

Safety Considerations

• This dosing regimen has been studied in over 150 pediatric patients with no significant adverse effects reported 1, 2
• Famotidine does not interact with cytochrome P450 enzymes, minimizing drug interaction concerns 2
• Monitor for symptom improvement; if no response after 2-4 weeks, reassess the diagnosis and consider alternative therapy

Important Caveats

• Renal function: If the infant has compromised renal function, dose reduction may be necessary as famotidine is 70% renally eliminated 3
• The pharmacokinetics in infants under 1 year are less well-studied than in older children, but available data support this weight-based approach 2
• Duration of treatment typically ranges from 4-8 weeks for most acid-related conditions in children 1