Ulinastatin on Systemic Immune-Inflammation in Patients With Complicated Intra-Abdominal Infection

Complicated intra-abdominal infection (cIAI) triggers dysregulated systemic inflammation and immune paralysis leading to high organ failure and death risk. Ulinastatin is a protease inhibitor with anti-inflammatory properties, but its dose-related effects on immune-inflammation of cIAI patients remain unclear. This single-center single-blinded three-arm randomized controlled pilot study enrolls adult cIAI patients (≥18 years, SOFA≥2) at Fujian Medical University Union Hospital. Eligible patients are randomized into low-dose ulinastatin, high-dose ulinastatin and normal saline placebo groups (1:1:1, 5 days intravenous treatment plus standard care), total planned enrollment 165 participants after 10% dropout adjustment. Primary endpoint is Day5 change of Systemic Immune-Inflammation Index (SII); secondary outcomes include serial inflammatory biomarkers, SOFA variation, organ dysfunction, hospitalization duration, 28-day mortality and safety profiles. This pilot aims to clarify ulinastatin's immune-modulating effect and inform future large RCT design.