Altered gentamicin pharmacokinetics in term neonates undergoing controlled hypothermia

Aim(s) Little is known about the pharmacokinetic (PK) properties of gentamicin in newborns undergoing controlled hypothermia after suffering from hypoxic-ischaemic encephalopathy due to perinatal asphyxia. This study prospectively evaluates and describes the population PK of gentamicin in these patients. Methods Demographic, clinical and laboratory data of patients included in a multicentre prospective observational cohort study (the 'PharmaCool Study') were collected. A non-linear mixed-effects regression analysis (nonmem®) was performed to describe the population PK of gentamicin. The most optimal dosing regimen was evaluated based on simulations of the final model. Results A total of 47 patients receiving gentamicin were included in the analysis. The PK were best described by an allometric two compartment model with gestational age (GA) as a covariate on clearance (CL). During hypothermia the CL of a typical patient (3 kg, GA 40 weeks, 2 days post-natal age (PNA)) was 0.06 l kg-1 h-1 (inter-individual variability (IIV) 26.6%) and volume of distribution of the central compartment (Vc) was 0.46 l kg-1 (IIV 40.8%). CL was constant during hypothermia and rewarming, but increased by 29% after reaching normothermia (>96 h PNA). Conclusions This study describes the PK of gentamicin in neonates undergoing controlled hypothermia. The 29% higher CL in the normothermic phase compared with the preceding phases suggests a delay in normalization of CL after rewarming has occurred. Based on simulations we recommend an empiric dose of 5 mg kg-1 every 36 h or every 24 h for patients with GA 36-40 weeks and GA 42 weeks, respectively.