This study aims to compare the clinical outcomes, safety and PD target attainment of the model-based dose and empirical dose of piperacillin/tazobactam in the treatment of LOS in premature neonates, so as to optimize the piperacillin/tazobactam dose regimen.

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.