BACTERICIDAL KINETICS OF AN IN-VITRO INFECTION MODEL OF ONCE-DAILY CEFTRIAXONE PLUS AMIKACIN AGAINST GRAM-POSITIVE AND GRAM-NEGATIVE BACTERIA

The in vitro efficacy of ceftriaxone plus amikacin combination against gram-positive and gram-negative bacteria, clinically isolated from pa tients affected by pneumonia in intensive care units, was compared to that of the 2 drugs used alone. The study was performed using a dynami c model in which the human kinetics of the drugs after intramuscular a dministration was simulated. The antibacterial activity was tested by determining the bacterial cell count (CFU/ml). Killing curves came out from plotting the log CFU/ml versus time. In the same way, ceftriaxon e and amikacin concentrations were assayed by HPLC and fluorescence po larization immunoassay, respective ly. The results show that ceftriaxo ne plus amikacin combination exert a high killing activity against all tested strains. The two antibiotics alone initially have a good killi ng activity but this is followed by bacterial regrowth for all tested isolates. This data supports the results of several clinical studies w hich have shown a good therapeutic efficacy of ceftriaxone plus amikac in combination in the treatment of severe infections caused by organis ms intermediately sensitive to these drugs.