Most patients with acute bronchitis receive a prescription for antibiotics, even though these medications are indicated in the treatment of bronchitis only when the patient has chronic lung disease. Acute bronchitis is viewed as a self-limited viral illness for which the use of antibiotics is generally not supported. However, the studies on which these recommendations are based generally had small sample sizes. Smucny and associates conducted a meta-analysis of all relevant English-language, randomized, controlled, blinded trials from 1966 to 1998 to evaluate the effectiveness of antibiotics in the treatment of acute bronchitis and to assess whether the risks of side effects outweigh the benefits of treatment.

Studies of patients with chronic bronchitis or those that did not include a placebo group were excluded from the analysis. Nine studies with a total of 779 patients met the inclusion criteria. Each study compared the effectiveness of a single antibiotic (e.g., doxycycline, erythromycin or trimethoprim-sulfamethoxazole) with a placebo. All trials performed one or more subgroup analysis, including age, duration of illness and smoking status.

No one patient subgroup was found to consistently benefit from antibiotic therapy. However, patients who were over 55 years of age and those who had a frequent cough and felt ill at study entry experienced some benefit from antibiotics. In addition, patients who received antibiotics were less likely to have a cough on follow-up examination and were less likely to be rated as unimproved by their physician. However, these findings did not necessarily have clinical importance. The incidence of adverse effects to antibiotics was also insignificant.

The authors conclude that antibiotics are only moderately beneficial and should not be prescribed routinely for acute bronchitis, given the conflicting data presented in these nine studies. A small group of patients may benefit from such treatment, but further research is needed to define this population. Currently, large randomized trials are under way to further address the issue. The authors recommend that physicians report the relative risks and benefits of antibiotic treatment to patients and allow them to be involved in management decisions until more definitive results are available.