Patients with chronic respiratory disease have increased susceptibility to infection, because of impairment of the local immunologic defense mechanism in the airway system, which often results in acute exacerbation. Acute exacerbation of chronic respiratory disease is one of the most important predictors of increased morbidity and mortality, and thus the management in the acute phase is essential for better prognosis. Although the clinical guidelines for the management of respiratory tract infections published by the Japanese Respiratory Society recommend administering fluoroquinolones intravenously in case of hospitalized patients, the clinical evidence is still limited. In this study, we evaluated the efficacy of Pazufloxacin Mesilate (PZFX). an intravenous fluoroquinolone. in patients with chronic respiratory diseases complicated with acute exacerbation caused by acute respiratory infections. As a result, 16 out of 18 cases were successfully treated with PZFX. No adverse event was observed during this study. These results may support the validity of administering intravenous fluoroquinolone in hospitalized patients with acute exacerbation caused by infections, as recommended by the Japanese Respiratory Society.