RESUMO
PURPOSE: Pneumococcus is one of the most important causes of invasive infection through the childhood period. In January 2008, the Clinical and Laboratory Standards Institute (CLSI) published revised penicillin breakpoints for Streptococcus pneumoniae and penicillin susceptibility rates of S. pneumoniae increased in Korea. This study was performed to determine the probability of oral amoxicillin for the empirical treatment achieving bactericidal exposure against pneumococcus using pharmacodynamics model. METHODS: Twenty-three isolates of pneumococci were subjected to determine minimum inhibitory concentration (MIC) for beta-lactams and macrolide. For the beta-lactams, exposure of fT >MIC (time that free drug concentrations remain above the MIC) for 50% of the administration interval have determined the probability of target attainment (PTA), and regimens that had a PTA >90% were considered optimal. An analysis was performed by applying MIC of 23 isolates to a 5000-patient Monte Carlo simulation model. RESULTS: Among 23 isolates from healthy children, 7 (30.4%) isolates were MIC 90% at MIC < or =1.0 microg/mL but PTA decreased to 52% at MIC 2 microg/mL, whereas amoxicillin 90 mg/kg/day can predict 97% of PTA at MIC 2 microg/mL. Overall, oral amoxicillin 90 mg/kg/day for the empirical treatment against pneumococcus can expect more successful response in Korean children. CONCLUSION: Considering the resistantce pattern of pneumococci in Korean children, we estimate that oral amoxicillin 90 mg/kg/day will provide a pharmacodynamic advantage for the empirical treatment against pneumococcus. And low dose amoxicillin or macrolide are expected to have higher chance of treatment failure than high dose oral amoxicillin.