Sivelestat sodium is primarily used as a selective inhibitor of neutrophil elastase, an enzyme that plays a significant role in inflammatory processes. Its main application is in the treatment of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), conditions often associated with severe inflammation and tissue damage in the lungs. By inhibiting neutrophil elastase, it helps reduce inflammation, prevent tissue degradation, and improve respiratory function. It is also studied for its potential use in managing other inflammatory conditions where neutrophil elastase activity is elevated, such as chronic obstructive pulmonary disease (COPD) and sepsis. Its therapeutic effects make it a valuable agent in critical care and respiratory medicine.