Inclusion Criteria:  Hospitalized infants and children from postmenstrual age of 38 weeks to age 19 years Requiring IV vancomycin, regardless of indication Parent or legally authorized representative is willing to provide permission and sign the informed consent document; subjects assent, when appropriate Hospitalized neonates, infants, children, adolescents who require, but have not been initiated on intravenous vancomycin therapy  Exclusion Criteria:  Patients who had received vancomycin during previous 2 weeks Patients with end-stage renal disease, receiving hemodialysis or receiving continuous renal replacement therapy On oral or intraperitoneal vancomycin Receiving extracorporeal therapy, including extracorporeal membrane oxygenation, continuous renal replacement therapy, and extracorporeal liver support Will only receive a single dose of vancomycin Known to be pregnant Is brain dead or has suspected brain death