The concentrations of cephalosporins in tissue fluid of rats with localized infection.

Rats implanted with multiperforated subcutaneous plastic capsules were used as a model for study of the penetration of four cephalosporins into sites infected with Escherichia coli. The concentrations of the antibiotics were determined in uninfected and infected cages microbiologically up to 4 h after treatment. All four cephalosporins entered infected capsules faster than the control ones and the peak concentrations were attained 30-60 min earlier. The clearance of the antibiotics from infected capsules was faster than from uninfected ones, probably due to inactivation by microbial beta-lactamase(s). Serum protein binding may account for differences in the penetration rate of cephalosporins, but serum level and serum half-time seem to contribute to their kinetic profile in tissue fluid.