Levels of rifampin and ciprofloxacin in nasal secretions: correlation with MIC90 and eradication of nasopharyngeal carriage of bacteria.
To predict the efficacy of antibiotics in eliminating nasopharyngeal carriage of organisms such as Neisseria meningitidis, Haemophilus influenzae, and methicillin-resistant Staphylococcus aureus (MRSA), a novel approach for measuring drug concentrations in nasal secretions was developed. Five healthy individuals received four doses of rifampin and then, at a later date, ciprofloxacin. At 2, 5, and 8 h after the last dose, serum, saliva, and cold-stimulated nasal secretion samples were collected, and drug levels were analyzed by high-performance liquid chromatography. Nasopharyngeal levels of rifampin reached but did not substantially exceed 90% of the minimal inhibitory concentration (MIC90) for H. influenzae, exceeded the MIC90 for N. meningitidis, and were well above that for MRSA. Ciprofloxacin levels in nasal secretions far exceeded the MIC90 for meningococci and Haemophilus organisms but were below that for MRSA. These findings are consistent with the clinical studies showing that rifampin eliminates, in most instances, the nasal carriage of N. meningitidis and to a lesser extent H. influenzae. A single dose of ciprofloxacin has been shown to eradicate meningococci, yet a long course of treatment with this drug is not adequate for MRSA. On the basis of these results, clinical trials with ciprofloxacin to eliminate nasopharyngeal carriage of H. influenzae appear to be warranted.