Model-based Dose Versus Empirical Dose of Piperacillin/Tazobactam in Preterm Neonates With Late-onset Sepsis.

Inclusion Criteria: * Preterm neonates: gestational age \<34 weeks; * Postnatal age \> 72h; * Postmenstrual age \<36 weeks; * Newly diagnosed as late-onset sepsis; * Parental written consent. Exclusion Criteria: * Patient with bacterial meningitis, osteomyelitis, septic arthritis or necrotizing enterocolitis requiring surgery. * High suspicion of/confirmed fungal infection. * Severe congenital malformations and/or severe organ failure. * Administration of any systemic antibiotic regimen 24 h before screening. * Administration of other systemic trial drug therapy. * Other factors that the researcher considers unsuitable for inclusion. * Post-randomization Exclusion: ①Patients with a positive baseline blood culture and the pathogen resistant to PIP/TAZO. ②Patients with bacterial meningitis, fungal infection, osteomyelitis, septic arthritis or necrotizing enterocolitis requiring surgery after randomization.