Is all free time above the minimum inhibitory concentration the same:: implications for β-lactam in vivo modelling

Previously, ertapenem 50 mg/kg every 6 h given subcutaneously to mice achieved a similar 24-h cumulative free time above the minimum inhibitory concentration (fT > MIC) to 1g every 24h in humans. However, this simplified regimen (SR) does not provide a superimposable concentration-time profile to that observed in humans, thus allowing concentrations to fluctuate above and below the minimum inhibitory concentration (MIC) throughout the 24-h period. Herein, we compared a complex regimen (CR; 9 various mglkg doses over 24 h) providing a near superimposable concentration-time profile with the SR to determine implications on bacterial kill against eight extended-spectrum beta-lactamase (ESBL)-producing isolates over a wide MIC range. The CR resulted in a similar ( +/- 5%) 24-h cumulative fT > MIC to ertapenem 1 g every 24 h in humans over an MIC range of 0.032 mg/L to 16 mg/L. Similar bacterial kill was observed with both regimens against all eight ESBL-producing isolates examined. In mouse models, it appears that the 24-h cumulativefr > MIC and not the distribution of theft > MIC over 24 h drives efficacy. (c) 2006 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved.