title: The effect of postnatal age on gentamicin pharmacokinetics in neonates.
abstract: OBJECTIVE
  To determine if gentamicin serum concentrations obtained from newborns on day 2 of life versus days 3-4 yield significantly different pharmacokinetic parameter values.
  
  
  METHODS
  Retrospective chart review.
  
  
  METHODS
  Neonatal intensive care unit.
  
  
  METHODS
  Two hundred and sixty-seven infants who had peak and trough gentamicin serum concentrations determined on days 2, 3, or 4 of life.
  
  
  METHODS
  Determination of peak and trough serum gentamicin concentrations on days 2, 3, or 4 of life.
  
  
  RESULTS
  The elimination rate constant, serum half-life, volume of distribution, and clearance of gentamicin were calculated using a one-compartment pharmacokinetic model. Gestational age, birthweight, gentamicin dosage, peak and trough gentamicin concentrations, and hours after birth at which serum concentrations were drawn were recorded for all infants. Infants were stratified into three groups based on gestational age: 28 weeks or younger, older than 28 weeks but younger than 37 weeks, and 37 weeks or older. Birthweight and calculated pharmacokinetic parameters were compared by 2-tailed Student t test to determine if significant differences existed between pharmacokinetics parameters determined on day 2 of life versus days 3 or 4 within each of the gestational age groups. These analyses revealed only one significant difference between parameters assessed on day 2 versus days 3 or 4: at day 2, the mean trough concentration of gentamicin in infants of gestational age between 28 and 37 weeks was 1.63 +/- 0.44 mg/L, whereas at days 3 or 4, the same parameter for patients of the same gestational age was 1.4 +/- 0.48 mg/L (p=0.005).
  
  
  CONCLUSIONS
  With one exception--elevated trough concentrations in infants in the gestational age group between 28 and 37 weeks--pharmacokinetic parameters calculated using gentamicin serum concentrations determined on day 2 of life are not significantly different from those derived from gentamicin serum concentrations determined on days 3 or 4. This suggests that gentamicin serum concentrations and subsequent dosage adjustments can be determined on day 2 of life.
authors.affiliation: Department of Pharmaceutical and Nutrition Services, Nebraska Health System, Omaha, USA.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Knight
authors.forename: Estella M
authors.initials: EM
authors.lastname: Davis
authors.forename: Konstantine
authors.initials: K
authors.lastname: Manouilov
authors.forename: Eric B
authors.initials: EB
authors.lastname: Hoie
mesh_terms: D000367:Age Factors; D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000493:pharmacokinetics*; D005839:Gentamicins / Q000008:administration & dosage / Q000493:pharmacokinetics*; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D007234:Infant, Premature; D007363:Intensive Care Units, Neonatal; D015278:Intensive Care Units, Pediatric; D012189:Retrospective Studies
chemical_list: D000900:Anti-Bacterial Agents; D005839:Gentamicins