Pharmacodynamic assessment of clarithromycin in a murine model of pneumococcal pneumonia

The pharmacodynamic profile of clarithromycin (CLR) was evaluated with a murine model of pneumonia. Eight Streptococcus pneumoniae isolates, including three macrolide-sensitive and five macrolide-resistant strains, were inoculated intratracheally into immunocompromised ICR mice as 10(8)-CFU bacterial suspensions. Orally administered CLR daily doses ranging from 5 to 600 mg/kg of body weight were given over 5 days, during which animal survival was monitored. The bacterial density in lung tissues was examined after 24 h of CLR treatment and in control groups. Pharmacokinetic analysis of CLR in mice demonstrated that the regimen of 150 mg/kg twice a day was representative of human pharmacokinetics and was used to compare the efficacy of CLR against sensitive and resistant S. pneumoniae strains. Immunocompetent CBA/J mice were also infected and treated as described above and evaluated for bacterial density and survival to assess the effect of the presence of leukocytes. All three pharmacodynamic parameters, the duration (percent) of the time that serum CLR concentrations remain above the MIC (%T>MIC), the ratio of the area under the concentration-time curve from 0 to 24 h (AUC(0-24)) to the MIC, and the ratio of the maximum concentration of drug in serum to the MIC, were found to be closely correlated to CLR bacterial efficacy (P < 0.001). Furthermore, all parameters had close correlation to bacterial density (r(2) = 0.72 to 0.82), median survival (r(2) = 0.93 to 0.94), and total percent survival (r(2) = 0.91 to 0.92). These in vivo data suggest that the bacterial activity of CLR is closely correlated with all three parameters over a wide range of exposures and, as a consequence of parameter interdependency, AUC(0-24)/MIC is the most reasonable predictor of antibiotic efficacy. In this neutropenic pneumonia model, CLR was less efficacious against S. pneumoniae strains for which MICs were greater than or equal to4 mug/ml. However, the presence of leukocytes in the immunocompetent mice resulted in improved bactericidal activity, relative to that in the neutropenic animals, despite an MIC of 4 mug/ml.