An in vitro pharmacodynamic model was used to determine the killing kinetics of cefpirome against 20 Streptococcus pneumoniae strains (penicillin G MICs, > 0.125 to 2 micrograms/ml) isolated from patients with meningitis. The concentration of cefpirome was adjusted dynamically to simulate the median concentration profile obtained in the cerebrospinal fluid of adults after the infusion of a single dose of 2 g. The cefpirome MIC at which 90% of isolates are inhibited was 0.5 microgram/ml. Bactericidal activity was observed at 6 h, with mean killing of 3.51 +/- 0.34 log10 CFU/ml for all strains for which the cefpirome MIC was < 0.5 microgram/ml. In contrast, for strains for which the cefpirome MIC was > or = 0.5 microgram/ml, killing was significantly less (P < 0.05), with a mean reduction of only 2.86 +/- 0.57 log10 CFU/ml.