Pharmacokinetics of tulathromycin in plasma and synovial fluid after regional intravenous administration in the bovine foot

Antimicrobial regional intravenous (RIV) perfusion may re­sult in high concentration of antimicrobial in the target tis­sues of deep digital sepsis. Nine crossbred, mature beef cows were administered tulathromycin as an RIV perfusion in the dorsal common digital vein of the left rear limb. Arthrocente­sis was performed of the lateral pouch of the left rear fetlock for 48 hours after antimicrobial administration. Pharmacoki­netic analysis of synovial fluid indicated that tulathromycin was able to achieve concentrations above the reported MIC50 of Fusobacterium necrophorum for approximately 18 hours post administration, but was unable to achieve concentrations above the MIC90. The AUC0-24/MIC50 was 41, while the AUC0-24/ MIC90 was 1.3 in synovial fluid. Although direct comparisons of MICs to achievable drug concentrations do not necessarily pre­dict efficacy, this study provides preliminary evidence for fur­ther evaluation of tulathromycin in cases of deep digital sepsis.