Tissue concentrations of antimicrobials. The site of action

The concentration of an antimicrobial drug at the site of infection is determined by its relative lipid solubility and the tissue in question. For drugs that are limited by their solubility to the extracellular fluid, the tissue concentrations in bone and soft tissue can be predicted from serum concentrations. Tissues with barriers to antimicrobial penetration include the prostate and central nervous system; there are special considerations when administering antimicrobials to treat infections in these areas or when intracellular drug concentrations are needed. Intermittent tissue concentrations of bactericidal antimicrobials that are 4-8 times the minimum inhibitory concentration (MIC) are usually sufficient for a clinical cure. However, there are situations when higher or more persistent drug concentrations are needed, such as when treating an immunosuppressed patient or when administering bacteriostatic drugs.