Vancomycin Pharmacokinetics and Dosing in Premature Neonates

Abstract

We prospectively studied the pharmacokinetic parameters of vancomycin in premature neonates given vancomycin according to a dosage protocol developed in our neonatal unit. Study infants were administered vancomycin according to four postconceptional age (PCA) groups: (0) 18 mg/kg every 36 h for PCA <27 weeks; (I) 16 mg/kg every 24 h for PCA 27–30 weeks; (II) 18 mg/kg every 18 h for PCA 31–36 weeks; and (III) 15 mg/kg every 12 h for PCA ≥37 weeks. Pharmacokinetic parameters were calculated from peak and trough serum vancomycin concentrations at steady state. Results in 44 infants (PCA, 27–44 weeks) showed that our dosage regimen achieved target peak serum vancomycin concentrations in 64% of neonates in Groups I-III, although it tended to undershoot the target trough concentrations. Volume of distribution (Vd), normalized for body weight, remained constant throughout the PCA range, with a mean value of 0.56 L/kg, whereas absolute clearance (r = 0.81) and normalized clearance (r = 0.48) increased with PCA (p < 0.005). The increase in clearance with PCA is associated with a greater elimination rate constant and shorter half-life. Vancomycin therapy can be initiated in a standard fashion according to our protocol or by individualizing the dosage regimen based on a Vd of 0.56 L/kg and clearance estimated from the infant's body weight and PCA groups.