[Antimicrobial susceptibility testing of bacteria isolated from animals: considerations concerning the predefinition of breakpoints from the clinical pharmacological viewpoint].

In vitro susceptibility tests are performed to receive information for selecting the most suitable antibacterial agent. As result of in vitro susceptibility tests, the minimum inhibitory concentration (MIC) indicates bacteria as resistant or sensitive. To determine MIC, therapeutically relevant breakpoints have to be defined. Microbiological criteria, chemical and physical characteristics as well as pharmacokinetic and toxicological (tolerance) properties of the antimicrobial compounds have to be considered in the selection of the therapeutic agent in addition to clinical experiences. Using some concentration and time dependent antibiotics as examples, it is demonstrated that the above mentioned criteria are not sufficiently considered in currently defined breakpoints.