LAUSR

BACKGROUND Acute phase protein (APP) measurement is used to detect inflammation. Intramuscular (IM) injections could cause tissue injury and induce an acute phase response. OBJECTIVES To evaluate the effects of IM procaine penicillin G (PPG) injections on APP concentrations in horses. STUDY DESIGN Prospective longitudinal design. METHODS PPG was administered intramuscularly to six horses, twice daily, for 5 days. Plasma fibrinogen (FIB), serum amyloid A (SAA), haptoglobin (HAP), creatine kinase (CK), and aspartate aminotransferase (AST) were quantified daily for 5 days before the first injection, during course of administration, and for 4 days after the final dose. Analytes were quantified every other day for the remaining 16 days. Data were compared using a parametric or non-parametric repeated measures ANOVA and a Tukey's or Mann-Whitney rank sum test, respectively. Significance was set at P<0.05. RESULTS CK was increased over baseline (mean ± SD: 200 ±74 IU/L) on days 1-6 (P<0.001 to P=0.02, mean ± SD: 723-1177 ± 355-544 IU/L) and AST was increased above baseline (mean ± SD: 233 ± 58 IU/L) on days 2-7 and 10 (P<0.001 to P=0.05, mean ± SD: 307-437 ± 79-146 IU/L). Increased FIB was noted over baseline (mean ± SD: 177 ± 30 mg/dL) on days 6-8 and 10 (P=0.02 to P=0.03, mean ± SD: 234-252 ± 33-49 mg/dL). SAA was increased above baseline (mean ± SD: 4.7 ± 2.9) on day 6 (P=0.02, mean ± SD: 113 ± 186 μg/mL). There was no change in HAP. MAIN LIMITATIONS Healthy horses used, small sample size, and lack of a negative control group. CONCLUSIONS Serial IM PPG injections may result in increased positive APP concentrations in horses and this must be considered when these test results are interpreted.