RATIONALE: COPD exacerbations are prone to non-recovery but there are no data about the effectiveness of retreatment on these prolonged events. We examined whether further therapy with ciprofloxacin for incompletely resolved COPD exacerbations prolonged the time until the next event. METHODS: This multi-centre randomised double-blind placebo-controlled trial studied retreatment with oral ciprofloxacin 500mg or matched placebo twice daily for 7 days in patients with GOLD stage II - IV COPD with persistent symptoms and/or serum C-reactive protein (CRP) ≥8mg/L initiated 14 (+/- 3) days after an index COPD exacerbation. The primary outcome was the time to the next exacerbation within a 90-day period. RESULTS: Of 826 patients screened at 4 centres, 144 eligible participants with incomplete recovery were randomised to receive ciprofloxacin (n=72) or placebo (n=72). 57% of patients in the ciprofloxacin group had experienced 1 or more exacerbations, compared to 53% in the placebo group. The median time to the next exacerbation was 32.5 days (IQR 13-50) in the placebo arm and 34 days (IQR 17-62) in the ciprofloxacin arm, which was not significantly different (adjusted hazard ratio = 1.07, 95% CI 0.68-1.68; p=0.76). No significant differences were seen in quality of life scores or lung function between treatment groups. CONCLUSION: In patients with persistent symptoms and/or raised CRP 14 days following a COPD exacerbation, an additional course of ciprofloxacin resulted in no additional benefit compared to placebo. This suggests that non-recovered exacerbations are not driven by ongoing bacterial infection and may potentially be targeted with anti-inflammatory therapy.