Population pharmacokinetics of propofol in neonates and infants: gestational and postnatal age to determine clearance maturation.

AIMS Develop a population pharmacokinetic model describing propofol pharmacokinetics in (pre)term neonates and infants, that can be used for precision dosing (e.g. during target controlled infusion (TCI)) of propofol in this population. METHODS A non-linear mixed effects pharmacokinetic analysis (Monolix 2018R2) was performed, based on a pooled study population in 107 (pre)term neonates and infants. RESULTS 836 blood samples were collected from 66 (pre)term neonates and 41 infants originating from three studies. Body weight (BW) of the pooled study population was 3.050 (0.580 - 11.440) kg, postmenstrual age (PMA) was 36.56 (27.00 - 43.00) weeks and postnatal age (PNA) was 1.14 (0 - 104.00) weeks (median and min-max range). A three compartment structural model was identified and the effect of BW was modeled using fixed allometric exponents. Elimination clearance maturation was modeled accounting for the maturational effect on elimination clearance until birth (by gestational age (GA)) and postpartum (by PNA and GA). The extrapolated adult (70 kg) population propofol elimination clearance (1.64 L min-1 , estimated relative standard error (RSE) = 6.02%) is in line with estimates from previous population pharmacokinetic studies. Empirical scaling of BW on the central distribution volume (V1 )in function of PNA improved the model fit. CONCLUSIONS It is recommended to describe elimination clearance maturation by GA and PNA instead of PMA on top of size effects when analyzing propofol pharmacokinetics in populations including preterm neonates. Changes in body composition in addition to weight changes or other physio-anatomical changes may explain the changes in V1 . The developed model may serve as a prior for propofol dose finding and TCI in (preterm) neonates.