The Pharmacometrics and Analytical Chemistry Core (PACC) will further the goals of this multidisciplinary UC San Diego MPRINT CET proposal by conducting highly coordinated research activities with the Clinical, Basic Research and Data Science Projects and the Milk Analytics Core, with guidance from the Administrative Core. Precise, high quality translation and clinical pharmacokinetic (PK) data will be generated to help address hypotheses raised in each of the Projects. The infrastructure enabling the PACC lies in the established and highly productive UC San Diego Pediatric Pharmacology Laboratory (PPL) within the Skaggs School of Pharmacy and Pharmaceutical Sciences and Department of Pediatrics. Specific Aims of the Clinical, Basic Science and Data Science Projects require quantification of antibiotics, their metabolites, and therapeutic effects markers in a variety of clinical and animal model matrices. The PACC is well qualified to conduct these quantitative assays and has experience with the small volumes and heterogeneous matrices associated with PK samples that will be generated by the Projects, including breastmilk. The PACC possesses prior and contemporary expertise in the processing of plasma, serum, whole blood, urine, cerebrospinal fluid, meconium, hair shaft, as well as all mammalian tissue types. Additionally, the PACC will continue to expand upon its capabilities to include quantification of drug metabolites in addition to their parent compounds. Quantification of drugs and metabolites in breast milk, plasma, and other matrices will be accomplished by LC-MS/MS and/or HPLC-UV. The PACC will also offer dedicated and specialized PK analysis to Project Leaders, including innovative PK modeling and simulation and physiologically-based PK (PBPK) modeling. Finally, the PACC will provide an optimal research and training environment in which to support the Clinical, Basic Science, and Translational Science Projects.