Exacerbations of chronic obstructive pulmonary disease (COPD) are an important 
cause of morbidity and healthcare expenditure. In hospitalized patients, 
antibiotics decrease treatment failure and reduce mortality. There is also 
evidence for the effectiveness of antibiotics in treating COPD exacerbations in 
the community, but this is most convincing in patients with severe airflow 
obstruction and there is uncertainty regarding the value of antibiotics in 
patients with mild airflow obstruction. Treatment with antibiotics is usually 
recommended for patients who have an increase in sputum volume, sputum purulence 
and breathlessness, but the most important determinant of bacterial infection 
appears to be purulence. There is some evidence to suggest that the decision to 
use antibiotics can be guided by the use of procalcitonin, although this needs 
to be confirmed in further studies. Newer broad-spectrum antibiotics may be more 
effective than older antibiotics but, because of concerns regarding antibiotic 
resistance, it may be appropriate to reserve them for patients at highest risk 
of treatment failure. A number of studies suggest that antibiotic courses of 5 
days in duration may be as effective as those for 7 days or more in patients 
with mild-to-moderate exacerbations of COPD. Guidelines do not recommend the use 
of prophylactic antibiotics in COPD but there is preliminary evidence to suggest 
that they may reduce the number of exacerbations. Until the full results of 
these studies are published, it will not be clear if they should be used.