2015 ACVIM Forum Research Abstract Program

46 horses treated with gentamicin and eight foals treated with amikacin were included. Peak and trough plasma concentration were measured 60 minute and 20 hour after administration. The MICs of gram-negative bacteria isolated in the hospital in 2014 were determined and compared to plasma concentrations. Backward stepwise logistic regression was used to identify factors associated with inadequate aminoglycoside peak concentrations. 43/46 (93%) horses reached a gentamicin peak of >16 lg/mL and 46/46 (100%) horses had a trough <2 lg/mL. 7/8 foals reached an amikacin peak of 32-40 lg/mL and 8/8 had a trough concentration of <2 lg/mL. Age (P = 0.006) and treatment failure (P = 0.03) were significantly associated with inadequate gentamicin peak concentrations, whereas presence of endotoxemia (P = 0.48) or prophylactic vs therapeutic use (P = 0.55) were not. 40/61 (65%) of gram negative bacteria were resistant to gentamicin (MIC ≥ 2 lg/mL). 47/61 (77%) of bacteria had a MIC of ≤4 lg/mL for amikacin.