Intermittent low-efficiency hemodiafiltration causes a marked decrease in ampicillin and sulbactam plasma concentration in dogs with oliguric acute kidney injury

Dogs with oliguric acute kidney injury (AKI) of infectious etiology are frequently managed with renal replacement therapy (RRT) and β-lactam antibiotics. Ampicillin and sulbactam are small, hydrophilic, renally eliminated molecules susceptible to extracorporeal clearance during RRT, yet the magnitude of their extracorporeal removal during RRT has not been quantified in dogs. Nine client-owned dogs with oliguric AKI of IRIS grade IV or greater that received ampicillin/sulbactam (22 mg/kg IV q8h) prior to undergoing low-efficiency hemodiafiltration (LE-HDF). Prospective, single-center observational study. Blood samples were collected immediately before and after the first LE-HDF session. Plasma ampicillin and sulbactam concentrations were quantified by validated LC-MS/MS and compared using a Wilcoxon signed-rank test; the relationship between pre- and post-dialysis concentrations was also characterized. Concentrations were interpreted against published minimum inhibitory concentration (MIC) thresholds for E. coli and Leptospira spp. LE-HDF reduced median ampicillin concentrations from 81.2 μg/mL (Interquartile range (IQR) 68.2-103.9) to 19.5 μg/mL (IQR 15.2-41.5), a median reduction of 75.6% (geometric mean ratio 0.23, 95% confidence interval (CI) 0.19-0.29), and sulbactam from 64.6 μg/mL (50.6-108.5) to 18.7 μg/mL (15.4-42.4; reduction 73.2%, geometric mean ratio 0.29, 95% CI 0.22-0.38). Post-dialysis ampicillin and sulbactam concentrations were strongly correlated with pre-dialysis concentrations (Spearman's ρ = 0.93 and 0.75, respectively). Despite this marked reduction, post-dialysis ampicillin concentrations exceeded all relevant MIC thresholds in all 9 dogs. A single LE-HDF session markedly reduces ampicillin and sulbactam concentrations in oliguric dogs, yet supratherapeutic baseline exposure maintained pharmacodynamic target attainment post-dialysis.