The chronic course and evolution of chronic obstructive pulmonary disease (COPD) is often characterized by periods of exacerbation of symptoms, which have a negative impact on the quality of life of patients, as well as on the evolution of COPD, and represent a significant cause of medical intervention and hospitalization. Very few data are available on the efficacy of rescue antibiotics in patients with acute exacerbation of COPD (AECOPD) unresponsive to previous treatment. The aim of this study was to evaluate the efficacy of two fluoroquinolones in AECOPD previously treated without success. The FADOI-FLOR study is a randomized, single-blind, non-inferiority comparison between levofloxacin and prulifloxacin. Primary end-point was "therapeutic success" at Day 10 of treatment, defined as disappearance of signs/symptoms or decrease of at least three points of a global score of symptomatology (maximum score = 15). 258 patients were enrolled (128 levofloxacin and 130 prulifloxacin), in 25 centers. A very high proportion of patients in the two groups had therapeutic success at Day-10 (levofloxacin 93.0% vs prulifloxacin 96.7%, population intention-to-treat; 94.6% vs 99.1%, population per-protocol). Earlier therapeutic success (within 7 days) was achieved in 32.0% and 36.2% of patients receiving levofloxacin or prulifloxacin, respectively. At 3-month follow-up, re-exacerbations occurred in 17.8% of patients treated with levofloxacin and 14.2% of those receiving prulifloxacin (p = 0.44). In conclusion, fluoroquinolones are very effective in the treatment of AECOPD resistant to other antibiotics.