Antibiotic treatment of bacterial exacerbation of chronic obstructive pulmonary disease (COPD) shows some immediate clinical benefits and may also minimise the frequency of further recurrences. Patients (n=511) were enrolled into a randomised double-blind multicentric study comparing the exacerbation-free interval (EFI), efficacy and safety of 7-day levofloxacin versus 10-day clarithromycin in patients with COPD exacerbation. Patients were monitored over a 1-yr period. A total of 434 patients (per protocol population) received the medication for > or =5 days. The median EFI in the per protocol population was 300 days for levofloxacin and 350 days for clarithromycin. For patients with a new documented exacerbation during follow-up (n=223), the median EFI was 100.5 days in the levofloxacin group and 95 days for clarithromycin. No significant differences in EFI between groups could be observed when stratifying the study population according to microbial aetiology and severity of bronchial obstruction. Levofloxacin and clarithromycin showed similar clinical success rates. The bacteriological success rate was significantly higher in the levofloxacin group. Both antibiotics were well tolerated. In summary, levofloxacin was associated with a significantly higher bacteriological eradication rate but similar exacerbation-free interval in patients with chronic obstructive pulmonary disease exacerbation compared to clarithromycin.