Abstract: We included 19 trials with 2663 participants (11 with outpatients, seven with inpatients, and one with ICU patients). For outpatients (with mild to moderate exacerbations), evidence of low quality suggests that currently available antibiotics statistically significantly reduced the risk for treatment failure between seven days and one month after treatment initiation (RR 0.72, 95% confidence interval (CI) 0.56 to 0.94; I² = 31%; in absolute terms, reduction in treatment failures from 295 to 212 per 1000 treated participants, 95% CI 165 to 277). Studies providing older antibiotics not in use anymore yielded an RR of 0.69 (95% CI 0.53 to 0.90; I² = 31%). Evidence of low quality from one trial in outpatients suggested no effects of antibiotics on mortality (Peto OR 1.27, 95% CI 0.49 to 3.30). One trial reported no effects of antibiotics on re-exacerbations between two and six weeks after treatment initiation. Only one trial (N = 35) reported health-related quality of life but did not show a statistically significant difference between treatment and control groups. Evidence of moderate quality does not show that currently used antibiotics statistically significantly reduced the risk of treatment failure among inpatients with severe exacerbations (i.e. for inpatients excluding ICU patients) (RR 0.65, 95% CI 0.38 to 1.12; I² = 50%), but trial results remain uncertain. In turn, the effect was statistically significant when trials included older antibiotics no longer in clinical use (RR 0.76, 95% CI 0.58 to 1.00; I² = 39%). Evidence of moderate quality from two trials including inpatients shows no beneficial effects of antibiotics on mortality (Peto OR 2.48, 95% CI 0.94 to 6.55). Length of hospital stay (in days) was similar in antibiotic and placebo groups. The only trial with 93 patients admitted to the ICU showed a large and statistically significant effect on treatment failure (RR 0.19, 95% CI 0.08 to 0.45; moderate-quality evidence; in absolute terms, reduction in treatment failures from 565 to 107 per 1000 treated participants, 95% CI 45 to 254). Results of this trial show a statistically significant effect on mortality (Peto OR 0.21, 95% CI 0.06 to 0.72; moderate-quality evidence) and on length of hospital stay (MD -9.60 days, 95% CI -12.84 to -6.36; low-quality evidence). Evidence of moderate quality gathered from trials conducted in all settings shows no statistically significant effect on overall incidence of adverse events (Peto OR 1.20, 95% CI 0.89 to 1.63; moderate-quality evidence) nor on diarrhoea (Peto OR 1.68, 95% CI 0.92 to 3.07; moderate-quality evidence). Researchers have found that antibiotics have some effect on inpatients and outpatients, but these effects are small, and they are inconsistent for some outcomes (treatment failure) and absent for other outcomes (mortality, length of hospital stay). Analyses show a strong beneficial effect of antibiotics among ICU patients. Few data are available on the effects of antibiotics on health-related quality of life or on other patient-reported symptoms, and data show no statistically significant increase in the risk of adverse events with antibiotics compared to placebo. These inconsistent effects call for research into clinical signs and biomarkers that can help identify patients who would benefit from antibiotics, while sparing antibiotics for patients who are unlikely to experience benefit and for whom downsides of antibiotics (side effects, costs, and multi-resistance) should be avoided.

Plain-language summary: Evidence gathered for this review is current to September 2018. We found 19 randomised studies that compared antibiotics versus placebo in a total of 2663 COPD patients with a wide range of flare-up severity. Analyses show that currently used antibiotics reduced treatment failures (no improvement in symptoms, despite treatment, within 7 to 28 days, depending on the study) compared with placebo in outpatients with mild to moderate flare-ups, as well as in patients admitted to an intensive care unit for very severe flare-ups with respiratory failure. However, antibiotics did not reduce treatment failures among hospitalised patients with severe flare-ups, although we are less certain about this result because the effect estimate also suggested findings similar to those seen in outpatients, but the confidence interval crossed 1.0. Use of antibiotics led to reduced mortality only in patients admitted to an intensive care unit, but not in patients with mild to moderate (outpatients) or severe (inpatients) flare-ups, although deaths were rare in these latter groups. Antibiotics did not reduce length of hospital stay for hospitalised patients. Patients treated with antibiotics experienced diarrhoea more often than those given placebo, but the difference was not statistically significant. Reviewers could not compare the severity of underlying COPD across trials because trial authors inconsistently reported lung function and other parameters. The quality of evidence for review outcomes was low to moderate. Although trial results show that antibiotics were effective across outcomes for patients with very severe flare-ups and respiratory failure who needed treatment in an intensive care unit, researchers report inconsistent effects in patients with mild to severe flare-ups. Future high-quality studies should examine clinical signs or blood tests at the time of presentation that are useful for identifying patients who can benefit from antibiotic therapy.