KRP-109 is a neutrophil elastase (NE) inhibitor with activity in reducing lung inflammation. KRP-109 improves survival in mouse models and reduces the number of neutrophils and inflammation in the alveolar walls. KRP-109 significantly reduced cell and neutrophil counts in bronchoalveolar lavage fluid, as well as cytokine levels such as interleukin 1β and macrophage inflammatory protein 2. KRP-109 can be used in the research of severe pneumonia.