Pharmacokinetic and Pharmacodynamic Modelling of Routinely Used Off Label Drugs in Premature Neonates

BACKGROUND Approximately 60% of drugs are used off--label in critically ill neonates in the Neonatal Intensive Care Units (NICU). This is even more true for pre--term born neonates in whom pharmacokinetics of these agents may be different due to immature elimination pathways. The lack of sufficient data about efficacy and safety of many of these drugs makes it difficult to have evidence based dosing guidelines for these agents. Therefore the urge for drug research in this population is of great importance. The pharmacokinetic (PK) and pharmacodynamic (PD) characteristics of drugs in premature infants are different from the characteristics found in term neonates, older children and adults. These differences are caused among others by a different body composition, by immaturity of the renal excretion systems, the metabolic pathways in the liver and other organ functions as well as immature drug receptors and transporters. After birth, there is a rapid development of many of these functions, necessitating frequent adaptation of dosage guidelines in the first few weeks of life. Besides age and size, co--morbidity, co--administration of drugs and genetic heterogeneity may further contribute to this extensive inter--individual variability in pharmacokinetics and pharmacodynamics of premature infants. There is a critical lack of evidence--based data of drug dosing in (extremely) preterm neonates.

OBJECTIVE Recently, population PK/PD modeling and simulation studies have enabled the development of evidence--based individualized dosing schemes for children with a limited number of subjects, thus improving drug safety and efficacy. The application of PK/PD modeling in the most critically ill population of premature infants, with the highest variability in the pharmacokinetics of drugs, and the greatest lack of adequate data underscoring optimal dosage, can contribute to the development of rational, individualized and safe dosing regimens.

This study will provide information on the pharmacokinetics, safety and effectiveness of off--label drugs used in critically ill premature infants: doxapram, fentanyl, midazolam, paracetamol, phenobarbital, sildenafil, levetiracetam, ibuprofen and fluconazole (only studied for the PK). PK/PD analysis will result in (adapted) dosage guidelines, thus contributing towards an improvement in the quality of care and cost efficiency. Furthermore the development of Dried Blood Spot (DBS) analysis is investigated for these drugs as a minimally invasive method for conventional patient care and to perform pharmacological studies in children. The adapted dosage guidelines will be implemented directly into clinical practice in collaboration with the NKFK. Therefore the study is designed as an observational multicenter study to be able to collect sufficient data for the drugs of interest.

DESIGN This is a prospective observational multicenter study on the pharmacokinetics and pharmacodynamics of paracetamol, fentanyl, midazolam, phenobarbital, doxapram, levetiracetam, sildenafil, ibuprofen and fluconazole routinely administered to preterm infants according to standard protocols. The treatment regimen is left to the discretion of the treating physician in accordance with current guidelines. During this study a limited number of additional blood samples will be drawn from the participants for pharmacokinetic analysis, never exceeding 3% of the total blood volume during any four--week period or 1% at any single time.

It is standard care in the Netherlands for all premature born infants under 32 weeks to get seen by the paediatrician at the age of two years for a check on growth and development. The visit to the day care clinic of the hospital of their admission on birth, enables us to collect qualitative data on growth and physiological development as well as from psychological and neurodevelopmental standardised tests.The collected data enables us to gain a better description of the subjects in our study and to further determine safety of the studied drugs.