Pharmacology of chronic obstructive pulmonary disease: antibiotics

The use of antibiotics in exacerbations of chronic obstructive pulmonary disease (ECOPD) is based on the finding of potentially pathogenic bacteria in sputum samples. Antibiotics remain an important part of treatment, but the validity of this approach for all patients is now being questioned. Using bronchoscopic methods, bacteria have been found to be absent from the lower airway in up to 50% of patients during exacerbations, suggesting that antibiotics may not be essential for all ECOPD. Antibiotic studies also suggest that they influence outcome in only a subgroup of patients. For an antibiotic to be active in ECOPD, it must reach the bacteria in either airway secretions or airway cells. The lipophilicity/hydrophilicity of the molecule is an important determinant of an antibiotic's ability to do this. It must not only reach the site but also do so at a concentration greater than the minimum inhibitory concentration (MIC) of the bacterium. For some antibiotics, the peak concentration is the best determinant of response, for others the proportion of the dose interval with antibiotic concentrations above the MIC is a better correlate. Studies have been hampered by the difficulties in measuring antibiotic concentrations in the different anatomical sites within the airways. Our knowledge is currently incomplete, but the above problems may now be being overcome.