Antibacterial kinetics of ampicillin against Escherichia coli under simulated in vivo conditions.

We studied the response of Escherichia coli to ampicillin concentrations which decreased logarithmically at elimination half-life values (t1/2a) ranging from one to four hours. The rate of bacterial killing depended on the initial antibiotic concentration (co), but was not significantly affected by t1/2a. Irrespective of co and t1/2a, the bactericidal effect terminated after about three hours of exposure to the drug.