Activities against Streptococcus pneumoniae of amoxicillin and cefotaxime at physiological concentrations: in vitro pharmacodynamic simulation.

An in vitro model simulating amoxicillin and cefotaxime concentrations in human serum (after standard doses) was used to explore the activities of these drugs over time against penicillin-susceptible and penicillin-resistant Streptococcus pneumoniae strains. An initial inoculum reduction percentage of > or = 90% was obtained with amoxicillin and maintained for 2 to 8 h, regardless of the strain tested. In contrast, experiments showed that cefotaxime had significantly (P < 0.001) less capability to reduce initial inocula of the penicillin-resistant pneumococci from 0.5 h on than amoxicillin, despite the same in vitro susceptibility to amoxicillin and cefotaxime in both strains.