Discrepancies between in vitro activity of and in vivo response to antimicrobial agents.

The correlation between in vitro antimicrobial activity and the in vivo response to antimicrobial therapy is affected by multiple host factors, the site and nature of the infection, and the pharmacokinetics of the antimicrobial and its penetration into areas of infection. In certain instances, discrepancies are also caused by methodologically-related variables of in vitro susceptibility tests. Examples of discrepancies between in vitro and in vivo response to antimicrobial are discussed.