Antibiotic levels in infected and sterile subcutaneous abscesses in mice

The pharmacokinetic properties of 10 antimicrobial agents were examined in sterile and infected encapsulated subcutaneous abscesses in mice. The inoculum for sterile abscesses was autoclaved cecal contents; that for infected abscesses was autoclaved cecal contents combined with Bacteroides fragilis. The antimicrobial agents examined were rosaramicin, clindamycin, chloramphenicol, metronidazole, and six beta-lactam antibiotics. All antimicrobial agents entered abscesses, produced peak levels of biological activity that were somewhat delayed in comparison to serum levels, and were present in negligible levels 8 hr after administration. The highest concentration in abscesses was achieved with rosaramicin and clindamycin, with peak levels of 43%--63% of the peak serum level. Peak levels of other antimicrobial agents in sterile abscesses were 13%--27% of the peak serum level. Levels of biologically active during were significantly lower in infected abscesses than in sterile abscesses for antimicrobial agents that are inactivated by B. fragilis beta-lactamase.