Background: Serum amyloid A (SAA), a major acute-phase protein in horses, is commonly used to monitor disease progression and guide treatment duration. Ceftiofur crystalline free acid (Excede®) is a widely used intramuscular (IM) antimicrobial in horses and SAA may be utilized to guide its use in diseased horses.
Hypothesis/
Objectives: We hypothesized that IM injections of Excede® would cause local inflammation resulting in increased concentrations of SAA, fibrinogen (FIB), creatine phosphokinase (CPK), and aspartate aminotransferase (AST).
Animals: Nineteen healthy adult horses.
Methods: In this prospective, longitudinal study, horses were administered two intramuscular injections of Excede® (6.6mg/kg) 4 days apart. Blood samples were collected daily from Day –2 to Day 12. SAA concentrations were measured daily using a commercial lateral-flow immunoassay (Stablelab®). FIB concentration was measured in sodium citrate plasma. Plasma CK and AST concentrations were measured using an automated biochemistry analyzer. Complete blood counts were obtained on days 0 and 14.
Results: Significant changes over time were observed for SAA (p < 0.0001), CPK (p=0.0015), and AST (p=0.0002). Fibrinogen did not differ significantly (p=0.4812). Increases in SAA ranged from mild to marked; 10/19 horses had mild increases (>20 but < 100 ug/ml), 5/19 had moderate increases (100-500ug/ml), and 4/19 showed marked increases (>500 ug/ml). Increases in CPK and AST were mild ( < 2x normal range).
Conclusions: IM injection of Excede® results in variable increases in SAA during a series of 2 injections. Clinicians should consider injection-associated increases when utilizing SAA to monitor disease and guide treatment decisions in horses receiving Excede®.
