Pharmacokinetics of famotidine in infants

Background: Although famotidine pharmacokinetics are similar in adults and children older than 1 year of age, they differ in neonates owing to developmental immaturity in renal function. Little is currently known about the pharmacokinetics of famotidine in infants aged between 1 month and 1 year, a period when renal function is maturing. Objective: To characterise the pharmacokinetics of famotidine in infants. Design: This was a two-part multicentre study with both single dose (Part I, open-label) and multiple dose (Part II, randomised) arms. Patients: Thirty-six infants (20 females and 16 males) who required treatment with famotidine and who had an indwelling arterial or venous catheter for reasons unrelated to the study. Methods: Infants in Part I were administered a single dose of famotidine 0.5 mg/kg; the dose was intravenous or oral according to the judgement of the attending physician. Infants receiving 0.5 mg/kg intravenously were divided into two groups by age, and pharmacokinetic parameters in infants 0-3 months and > 3 to 12 months of age were compared. Infants in Part II were randomised to one of the following treatments: 0.25 mg/kg/dose intravenously or 0.5 mg/kg/dose orally on day 1 and subsequent days, or 0.25 mg/kg/dose intravenously or 0.5 mg/kg/dose orally on day I followed by doses of either 0.5 mg/kg/dose intravenously or 1 mg/ kg/dose orally on subsequent days. From day 2 onwards, age-adjusted dose administration regimens (once daily in infants < 3 months of age and every 12 hours in infants > 3 months of age) were used; the total number of famotidine doses ranged from 3 to II and the total number of days of dose administration ranged from two to eight. Results: In infants < 3 months of age, plasma and renal clearance of famotidine were decreased compared with infants > 3 months of age. Pharmacokinetic parameters for the older infants (i.e. those > 3 months) were similar to those previously reported for children and adults. Approximate dose-proportionality, no accumulation on multiple dosing and an estimated bioavailability similar to adult values were also observed. Conclusion: A short course of famotidine therapy in infants appears generally well tolerated, and the characteristics of famotidine pharmacokinetics during the first year of life are explained to a great degree by the development of renal function, the primary route of elimination for this drug.