Vancomycin is already used for decades in neonates. However, there are remaining questions concerning vancomycin disposition in this population. The purpose of this study is first of all to perform a paired analysis of serum vancomycin concentrations using an immunoassay versus a reference liquid chromatography-tandem mass spectrometry method. Secondly, we aim to determine vancomycin protein binding and its covariates in neonates.

Exploration of vancomycin disposition in neonates:

Objective 1: Paired analysis of (total) serum vancomycin concentrations in neonates using the currently available immunoassay (Cobas c702) versus a reference liquid chromatography-tandem mass spectrometry method (LC-MS/MS).

Objective 2: The determination of vancomycin protein binding and its covariates in neonates.

Inclusion Criteria:

• Neonates, admitted to the Neonatal Intensive Care Unit to whom vancomycin is administered for medical reasons, can be included in the study after informed consent of the parents.

Exclusion Criteria:

• No vancomycin therapy
• No signed informed consent available