Determinants of response to antibiotic therapy.

The in vivo situation is far more complex than that of the standard in vitro susceptibility test yet in vitro tests have stood the test of time and are often good predictors of clinical outcome. Nevertheless, our understanding of the pharmacodynamics of antibiotic microbe interaction are giving us new insights into how to improve our performance and interpretation of these tests. These factors include consideration of inoculum effect, antibiotic interactions, cidal effects and the area under the inhibitory time curve (AUIC). There are however other variables which it is difficult to incorporate into in vitro tests, especially the immune status of the patient, which can be crucial to outcome. While the immune system can be boosted in certain instances, e.g. by growth factors or immunoglobulin infusions, our ability to modify the immune response to infection has been frustrated. Understanding the interaction of antibiotics with the immune system and the consequences of the differing actions of the various antibiotic classes on the immune response is another door that is opening for the future.