Vancomycin is the critically important antibiotic to treat neonatal Late Onset Sepsis (LOS) due to Gram positive bacteria in neonates, including Coagulase Negative Staphylococci (CoNS) and Staphylococcus aureus. These organisms also create biofilms which are extremely resistant to antibiotics. The increased incidence of LOS due to bacteria such as CoNS and MRSA in NICUs has led to a marked increased use of vancomycin, which is now the third commonest antibiotic used in European NICUs. However, a standardised dosing regimen for premature infants has not yet been defined and there is no data about the serum concentrations needed to ensure bacterial kill for CoNS in humans. In view of the lack of any firm dosage for neonates and infants, vancomycin has been included in the EMA list of off-patent drugs addressing unmet therapeutic needs in children. Accordingly NeoVanc consortium has already submitted a Paediatric Investigation Plan (PIP) which has provisionally received a favourable 120 day opinion and this application is built on what is included in the approved PIP. This project aims to:-develop a new age-appropriate formulation of vancomycin; define the circulating concentration of vancomycin that is needed to kill CoNS in in vitro biofilm and animal model, and use that data to derive the concentration and best PD target that will be maximally effective in neonates; define the neonatal dosage that is needed to attain the concentration that can kill CoNS and enterococci by conducting a systematic meta-analysis of all available PK data and develop an optimal dosing and therapeutic drug monitoring regimen. NeoVanc will then conduct a Phase 2 b randomised clinical trial to compare the proportion of neonates reaching the PD target derived from the pre-clinical studies when treated with the current standard vs new “optimised” treatment regimens and to obtain data on dosing, efficacy and short and long-term safety to be included in the SPCs leading to a PUMA.