Antibiotic pharmacokinetic considerations in pulmonary infections.

The factors affecting the penetration of antibiotics into the respiratory tract and their clinical relevance in treating pulmonary infections are discussed in this article. The importance and interpretation of sputum, bronchial fluid, pleural fluid, and lung tissue levels are emphasized, including a tabular summary of published data on antibiotic levels in the respiratory tract. The relative predictive efficacy of antibiotics against pulmonary pathogens is best expressed by comparing tissue levels with the mean minimum inhibitory concentration of the infecting organism, ie, the "kill ratio." The kill ratio is the best way to compare dissimilar antibiotics in terms of their likely efficacy in treating pulmonary infections, ie, those with high kill ratios (greater than or equal to 2) are more likely to be associated with a favorable clinical outcome than those with lower kill ratios. The difficulties with interpreting pharmacokinetic data from various parts of the respiratory tract in terms of specimen timing, handling, processing, and interpretation are also discussed in this article.