Determination of synovial fluid and serum concentrations, and morphologic effects of intraarticular ceftiofur sodium in horses.

Objectives— To determine the serum and synovial fluid concentrations of ceftiofur sodium after intraarticular (IA) and intravenous (IV) administration and to evaluate the morphologic changes after intraarticular ceftiofur sodium administration. Study Design— Strip plot design for the ceftiofur sodium serum and synovial fluid concentrations and a split plot design for the cytologic and histopathologic evaluation. Animals— Six healthy adult horses without lameness. Methods— Stage 1: Ceftiofur sodium (2.2 mg/kg) was administered IV. Stage 2: 150 mg (3 mL) of ceftiofur sodium (pHavg 6.57) was administered IA into 1 antebrachiocarpal joint. The ceftiofur sodium was reconstituted with sterile sodium chloride solution (pH 6.35). The contralateral joint was injected with 3 mL of 0.9% sterile sodium chloride solution (pH 6.35). Serum and synovial fluid samples were obtained from each horse during each stage. For a given stage, each type of sample (serum or synovial fluid) was collected once before injection and 12 times after injection over a 24-hour period. All horses were killed at 24 hours, and microscopic evaluation of the cartilage and synovium was performed. Serum and synovial fluid concentrations of ceftiofur sodium were measured by using a microbiologic assay, and pharmacokinetic variables were calculated. Synovial fluid was collected from the active joints treated during stage 2 at preinjection and postinjection hours (PIH) 0 (taken immediately after injection of either the ceftiofur sodium or sodium chloride), 12, and 24, and evaluated for differential cellular counts, pH, total protein concentration, and mucin precipitate quality. Results— Concentrations of ceftiofur in synovial fluid after IA administration were significantly higher (P = .0001) than synovial fluid concentrations obtained after IV administration. Mean peak synovial fluid concentrations of ceftiofur after IA and IV administration were 5825.08 μg/mL at PIH .25 and 7.31 μg/mL at PIH 4, respectively. Mean synovial fluid ceftiofur concentrations at PIH 24 after IA and IV administration were 4.94 μg/mL and .12 μg/mL, respectively. Cytologic characteristics of synovial fluid after IA administration did not differ from cytologic characteristics after IA saline solution administration. White blood cell counts after IA ceftiofur administration were ≤3,400 cells/μL. The mean synovial pH of ceftiofur treated and control joints was 7.32 (range, 7.08–7.5) and 7.37 (range, 7.31–7.42), respectively. Grossly, there were minimal changes in synovium or cartilage, and no microscopic differences were detected (P = .5147) between ceftiofur-treated joints and saline-treated joints. The synovial half-life of ceftiofur sodium after IA administration joint was 5.1 hours. Conclusions— Synovial concentrations after intraarticular administration of 150 mg of ceftiofur sodium remained elevated above minimal inhibitory concentration (MIC90) over 24 hours. After 2.2 mg/kg IV, the synovial fluid ceftiofur concentration remained above MIC no longer than 8 hours. Clinical Relevance— Ceftiofur sodium may be an acceptable broad spectrum antimicrobial to administer IA in septic arthritic equine joints.