[Bactericidal activity of amoxicillin and cefaclor in an "in vitro" kinetic model (author's transl)]

The bactericidal activity against Staphylococcus aureus 290-P, Escherichia coli NIHJ-JC2 and Klebsiella pneumoniae ATCC-10031 (10(6)/ml) was studied during 24 h, using an in vitro kinetic model which simulates the drug concentrations occurring in human serum after oral doses of amoxicillin (0.5 g or 1 g) or cefaclor (0.25 g or 0.50 g), 2 or 3 times a day. After the first antibiotic exposure, a high level of bactericidal activity (99-99.9%) was observed. Complete bactericidal activity was observed in all cases against S. aureus, but only after 3 times per day exposures in the case of E. coli and K. pneumoniae. Twice per day exposures of amoxicillin or cefaclor were invariably ineffective for these two species of Enterobacteriaceae (10(9) bacterial survivors/ml). These findings were related to subinhibitory concentrations which were or not able to prevent or reduce the bacterial regrowth after the first exposure of the antibiotics.