Distribution of ceftiofur into Mannheimia haemolytica-infected tissue chambers and lung after subcutaneous administration of ceftiofur crystalline free acid sterile suspension.

The objective of this study was to evaluate the penetration of ceftiofur- and desfuroylceftiofur-related metabolites (DCA) into sterile and infected tissue chambers, lung tissue and disposition of DCA in plasma across four different sacrifice days postdosing. Twelve healthy calves were utilized following implantation with tissue chambers in the paralumbar fossa. Tissue chambers in each calf were randomly inoculated with either Mannheimia haemolytica or sterile PBS. All calves were dosed with ceftiofur crystalline free acid sterile suspension (CCFA-SS) subcutaneously in the ear pinna. Calves were randomly assigned to 4 groups of 3 to be sacrificed on days 3, 5, 7 and 9 postdosing. Prior to euthanasia, plasma and tissue chamber fluid were collected, and immediately following euthanasia, lung tissue samples were obtained from four different anatomical sites DCA concentration analysis. Results of our study found that, in general, DCA concentrations followed a rank order of plasma > infected tissue chamber fluid > noninfected tissue chamber fluid > lung tissue. Data also indicated DCA concentrations remained above the therapeutic threshold of 0.2 microg/mL for plasma and chamber fluid and 0.2 microg/g for lung tissue for at least 7 days post-treatment.