Abstract

Background
：It is important to select appropriate antimicrobials for the treatment of infection according to the results of antibiotic susceptibility test(AST). AST interprets as susceptible, resistant or intermediate on the base of breakpoints of Clinical and Laboratory Standard Institute(CLSI), but do not take into account the antimicrobial concentrations of variable tissues. As different tissues have different distributions of antimicrobials, it is necessary to interpret AST according to the tissue concentration. Thereby we intend to evaluate the usefulness of interpretation of antimicrobial susceptibility depending on tissue distribution of antimicrobials. Materials and Methods：Gram negative bacilli that isolated from clinical specimens in Yeungnam University Hospital from August to September, 2007 were evaluated retrospectively. The data of blood concentration and tissue distribution of antibiotics with variable administration route and dosage were collected and arranged in the forms of previous reported data and regarded as resistant if minimal inhibitory concentration (MIC) is higher than the expected concentration of each tissues.
Results
：Among the data reported as susceptible, aztreonam, imipenem and ciprofloxacin were relatively good relationship with AST. But, ampicillin, ticarcillin, cefazolin and cefotaxime of sputum or bronchial secretion were less effective with high MIC of organism. Gentamicin and amikacin also were shown as less effective in respiratory tissues and wound with high MIC of oganism.
Conclusion
：As different tissues have different antimicrobial concentrations for identical antimicrobial, more informations on antimicrobial tissue distribution is needed for appropriate treatment in infection. Reporting of MIC should be considered for selection of antimicrobials rather than AST with breakpoints. Therefore interpretation of AST considering tissue concentration is more helpful for prevention of major error and control of infection.

• Keywords: Antimicrobial concentration, Tissue, Antibiotic susceptibility test