Famotidine Dosing for a 3-Month-Old Infant Weighing 12 Pounds
For a 3-month-old infant weighing 12 lb (5.4 kg), administer famotidine 0.5 mg/kg once daily, which equals approximately 2.7 mg once daily. 1
Age-Specific Dosing Rationale
Infants under 3 months of age require once-daily dosing due to immature renal function, which significantly decreases both plasma and renal clearance of famotidine compared to older infants. 1
Infants older than 3 months can receive famotidine every 12 hours, as their pharmacokinetic parameters approach those of older children and adults. 1
At 3 months of age, this infant sits at the transition point; conservative once-daily dosing is safer given the prolonged elimination half-life in younger infants. 1
Dose Calculation and Administration
Calculate the dose: 0.5 mg/kg × 5.4 kg = 2.7 mg once daily 1, 2
The dose can be administered either intravenously or orally, depending on clinical circumstances and the infant's ability to tolerate oral medications. 1
Oral bioavailability is approximately 50% in infants, similar to adult values, so oral dosing at 0.5 mg/kg is appropriate. 1, 3
Dose Adjustment Considerations
If inadequate response occurs after initial treatment, the dose may be individualized upward to 1.0 mg/kg once daily for infants under 3 months, though 0.5 mg/kg is the recommended starting dose. 2
Once the infant reaches 3 months of age and demonstrates adequate renal maturation, transition to twice-daily dosing (0.5 mg/kg every 12 hours) may provide better acid suppression. 1, 4
Safety Profile
Famotidine is generally well tolerated in infants, with the most common adverse effects being agitation, irritability (sometimes manifested as head-rubbing), somnolence, and anorexia. 2
No serious adverse events have been reported in controlled trials of infants receiving famotidine at these doses. 2
Unlike cimetidine and ranitidine, famotidine does not interact with cytochrome P450 enzymes, reducing the risk of drug interactions. 4
Clinical Efficacy
At 0.5 mg/kg dosing, famotidine significantly improves regurgitation frequency in infants with gastroesophageal reflux disease. 2
The 1.0 mg/kg dose may provide additional benefit for crying time and regurgitation volume, but should be reserved for cases with inadequate response to the lower dose. 2
Treatment duration of 8 weeks has demonstrated ulcer healing and symptom resolution in pediatric patients. 3
Important Caveats
Renal function is the primary determinant of famotidine clearance, and the dramatic developmental changes in renal function during the first year of life necessitate age-adjusted dosing. 1
Famotidine neutralizes gastric acidity during sleep but may not continuously maintain intragastric pH >5.0 throughout the day, even with twice-daily dosing in older infants. 3
For infants weighing less than 10 kg (22 lb), some clinicians have used three-times-daily dosing, though this is based on older literature and may not be necessary with current dosing recommendations. 5