Abstract: Four randomised trials were eligible for inclusion in this systematic review - two studies with 83 adults comparing fluoroquinolones with β-lactams and two studies with 55 adults comparing aminoglycosides with polymyxins. None of the included studies reported information on exacerbations - one of our primary outcomes. Included studies reported no serious adverse events - another of our primary outcomes - and no deaths. We graded this evidence as low or very low quality. Included studies did not report quality of life. Comparison between fluoroquinolones and β-lactams (amoxicillin) showed fewer treatment failures in the fluoroquinolone group than in the amoxicillin group (OR 0.07, 95% CI 0.01 to 0.32; low-quality evidence) after 7 to 10 days of therapy. Researchers reported that Pseudomonas aeruginosa infection was eradicated in more participants treated with fluoroquinolones (Peto OR 20.09, 95% CI 2.83 to 142.59; low-quality evidence) but provided no evidence of differences in the numbers of participants showing improvement in sputum purulence (OR 2.35, 95% CI 0.96 to 5.72; very low-quality evidence). Study authors presented no evidence of benefit in relation to forced expiratory volume in one second (FEV₁). The two studies that compared polymyxins versus aminoglycosides described no clear differences between groups in the proportion of participants with P aeruginosa eradication (OR 1.40. 95% CI 0.36 to 5.35; very low-quality evidence) or improvement in sputum purulence (OR 0.16, 95% CI 0.01 to 3.85; very low-quality evidence). The evidence for changes in FEV₁ was inconclusive. Two of three trials reported adverse events but did not report the proportion of participants experiencing one or more adverse events, so we were unable to interpret the information. Limited low-quality evidence favours short-term oral fluoroquinolones over beta-lactam antibiotics for patients hospitalised with exacerbations. Very low-quality evidence suggests no benefit from inhaled aminoglycosides verus polymyxins. RCTs have presented no evidence comparing other modes of delivery for each of these comparisons, and no RCTs have included children. Overall, current evidence from a limited number of head-to-head trials in adults or children with bronchiectasis is insufficient to guide the selection of antibiotics for short-term or long-term therapy. More research on this topic is needed.

Plain-language summary: In April 2018, we looked for studies including adults or children with bronchiectasis that randomly allocated participants to receive one antibiotic or another by the same method of administration. We found only four studies, and they were very small. In total, they included 138 participants. This small sample makes it very difficult to draw clear conclusions. Four randomised trials were eligible for inclusion in this systematic review. None of the included studies reported information on flare-ups (exacerbations). Included studies reported no deaths and no serious adverse events. Treatment failures were fewer with fluoroquinolone antibiotics than with amoxicillin antibiotics. Reviewers considered the quality of the evidence provided by the four small included studies to be low or very low. Fluoroquinolone antibiotics may be more successful than amoxicillin antibiotics in treating exacerbations, but this finding is based on low-quality evidence. More evidence from high-quality clinical trials of short-term and long-term treatment with antibiotics is needed if clear conclusions are to be reached on the benefits of one antibiotic over another for people with bronchiectasis.