The Impact of Hypothermia on the Pharmacokinetics of Drugs Used in Neonates and Young Infants.

Therapeutic hypothermia (HT) is frequently used in neonates with hypoxic-ischemic encephalopathy and young infants during cardiopulmonary bypass (CPB). Hypothermia and CPB result in physiological changes contributing to pharmacokinetic (PK) and pharmacodynamic (PD) changes. Changes in the absorption, the volume of distribution (Vd) and the total body clearance (CL) of drugs used during hypothermia and CPB might lead to the interindividual PK variability resulting in either insufficient or toxic plasma concentrations and have an impact on the biodisposition and action of drugs. Both under- or overdosing of medicines in these critically ill patients may contribute to a worse overall outcome. Overall, hypothermia decreases CL but may decrease or increase Vd by changing intravascular blood volume, organ perfusion and enzymatic metabolic processes. In addition, maturational as well as organ specific changes may occur during hypothermia superimposed on the underlying disease and/or procedures such as extracorporeal membrane oxygenation (ECMO) or CPB. This paper will provide an overview of variables and potential covariates (e.g., asphyxia, sepsis, multiorgan dysfunction syndrome, cardiac arrest) determining the PK of frequently used drugs. In addition, the effects of hypothermia on individual drugs are described as well as alternative ways for future study designs such as the use of population PK-PD and opportunistic sampling. Ultimately, these investigations are warranted to obtain specific dosing nomograms of medicines for use in clinical practice and to improve the treatment results of this vulnerable group of pediatric patients.