Evidence from randomized controlled trials (RCTs) suggests that antibiotics have a modest benefit for people who have been diagnosed with acute bronchitis. However, acute bronchitis is a self-limiting condition, and this slight benefit should be considered in the wider context of drug-induced adverse effects, and the increased likelihood of pathogens developing resistance in the individual and in the community. There is no good evidence from RCTs to support the use of one antibiotic over another in the treatment of acute bronchitis.

• A Cochrane review (search date: March 2004) identified nine RCTs (n = 750) that compared the effectiveness of an antibiotic with placebo in people diagnosed with acute bronchitis aged 8–65 years [Fahey et al, 2004]. The quality of the trials was variable. The antibiotics studied were doxycyline (four studies); erythromycin (four studies); and co-trimoxazole, azithromycin, and cefuroxime (one study each).
• Various outcomes were reported with the following results:
• Cough: people taking an antibiotic were less likely to have a cough, with a relative risk of 0.64 (95% CI 0.49 to 0.85). This meant five people would need to be treated with an antibiotic for one person to present at follow up without a cough (NNT = 5, 95% CI 3 to 14).
• Global improvement and lung function: people taking an antibiotic were less likely to be unimproved (according to physicians' assessment) at follow up (RR 0.46, 95% CI 0.31 to 0.67) or have abnormal lung function (RR 0.54, 95% CI 0.41 to 0.70).
• Duration of symptoms: taking an antibiotic reduced the duration of cough by an average of 0.58 days (95% CI 0.01 to 1.16), and reduced the duration of feeling ill by 0.58 days (95% CI 0.00 to 1.16).
• Adverse effects were not significantly increased by antibiotics in the studies included, although there was a trend towards this (RR 1.22, 95% CI 0.94 to 1.58). The most common adverse effects were gastrointestinal disturbance, headaches, skin rash, and vaginitis. However, less than 4% of people were reported as dropping out of the trials due to adverse effects.
• The authors concluded that although antibiotics were seen to be of benefit in people with acute bronchitis, the magnitude of this benefit has to be weighed against the disadvantages of antibiotic use including adverse effects, medicalization of a self-limiting illness, and the risk of resistance developing.
• CKS were unable to find any head-to-head RCTs that would enable a direct comparison to assess the relative effectiveness of different antibiotics in treating acute bronchitis.