Antimicrobial drugs are designed to selectively inhibit or kill microbes. These are measured by the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC), respectively. They include:
The therapeutic window is from 10% of therapeutic effect to 10% of the toxic effect.
Antimicrobials are selected based on their activity against a given pathogen. However, there are many other factors which need to be considered:
Antibiotics can be given prior to organism identification based on clincial picture and epidemiology, local rates of resistance, and severity of disease. Combination therapy may be used as emperic therapy.
Combination therapy can be used to treat polymicrobial infections, as initial emperic therapy, for synergistic effects, or to prevent resistance. However, combination therapy can also cause antagonistic effects, can induce resistance in some cases, or cause drug interactions with risk of side effects.