Endotoxin release after antimicrobial treatment in sick foals is mediated by antimicrobial class

The objective of this study was to determine whether treatment with antimicrobials leads to increased serum endotoxin concentrations in sick foals and to further determine whether an effect of class of antimicrobial on endotoxin release occurs in sick foals in vivo. This was a prospective, observational study at a university equine hospital. Twenty-four foals aged 12 hours to 12 days admitted to the hospital in 2004 and 2005 were used. Blood was collected from all foals at time 0 (admission) and at 30 minutes, 8 hours, 12 hours, and 24 hours after treatment with an antimicrobial. The choice of antimicrobial was determined by the clinician caring for the foal, and any other treatment, as deemed necessary for appropriate care of the foal, was employed. For each serum sample, the endotoxin concentration was determined using the limulus amebocyte lysate assay. Those foals that received a beta-lactam alone, more specifically the cephalosporin ceftiofur, showed a significant increase in endotoxin concentration 12 hours after antibiotic administration (P = .005). An increase in serum endotoxin concentration was not seen in the first 24 hours after antimicrobial administration when foals were treated with a combination of beta-lactam and aminoglycoside antimicrobials. In conclusion, a significant increase in endotoxin concentration as a consequence of ceftiofur administration occurs in sick foals. Administration of a combination of a beta-lactam antimicrobial and an aminoglycoside did not result in a significant increase in endotoxin release. Consideration of these findings should be made when choosing antimicrobial therapy for the sick foal.