In vitro postantibiotic effects following multiple exposures of cefotaxime, ciprofloxacin, and gentamicin against Escherichia coli in pooled human cerebrospinal fluid and Mueller-Hinton broth. Antimicrob. Agents Chemother

Multiple exposures with cefotaxime in either Mueller-Hinton broth or cerebrospinal fluid had no effect on killing or the duration of postantibiotic effect (PAE) in Escherichia coli strains tested. However, upon multiple exposures in Mueller-Hinton broth, ciprofloxacin and gentamicin PAEs significantly decreased with a concomitant reduction in bacterial killing. A reduction in bacterial killing following multiple ciprofloxacin and gentamicin exposures was also seen with cerebrospinal fluid; however, the PAE was maintained. The postantibiotic effect (PAE) describes the suppression of bacterial growth subsequent to antimicrobial agent re-moval. The significance of the PAE as a parameter important in the description of antimicrobial activity is increasingly being recognized (1, 2, 12, 14). Many antimicrobial agents demonstrate a PAE in vitro and in vivo following a single exposure, but data elucidating multiple-exposure PAEs are limited (10). In addition, the majority of in vitro PAE determinations have been ascertained with standard micro-biological media such as Mueller-Hinton broth (MHB) (2