Vancomycin pharmacokinetics in infants: relationship to postconceptional age and serum creatinine.

Multidose pharmacokinetics of vancomycin were studied in 15 infants with gestational age less than 36 weeks and suspected or confirmed Staphylococcus epidermidis infections. Postconceptional age (PCA) at the time of the study ranged from 26 to 44 weeks. Vancomycin individual doses ranged from 6.7 to 10.6 mg/kg and were infused over 60 min. Five postinfusion samples were obtained in 13 infants, while 4 samples were obtained in 2 patients. Vancomycin pharmacokinetic parameters were determined by fitting the data to a two-compartment model using a weighted least-squares nonlinear regression method. Mean vancomycin body clearance (CL), volume of distribution (Vdss) and terminal elimination half-life were 1.37 ml/min, 0.58 liters and 5.6 h, respectively. When standardized for patient weight, the CL and Vdss values were 1.07 ml/min/kg and 0.48 liters/kg, respectively. The CL (ml/min/kg) was strongly inversely correlated with the serum creatinine (r = -0.82), while a weaker but significant association was noted with PCA (r = 0.41). These data suggest that in sick infants, in addition to the PCA, serum creatinine should be considered when determining the initial vancomycin dosing regimen.