Comparison of pharmacokinetic variables for creatinine and iohexol in dogs with various degrees of renal function.

Objective-To compare pharmacokinetics and clearances of creatinine and iohexol as estimates of glomerular filtration rate (GFR) in dogs with various degrees of renal function. Animals-50 Great Anglo-Francais Tricolor Hounds with various degrees of renal function. Procedures-Boluses of iohexol (40 mg/kg) and creatinine (647 mg/kg) were injected IV. Blood samples were collected before administration and 5 and 10 minutes and 1, 2, 4, 6, and 8 hours after administration. Plasma creatinine and iohexol concentrations were assayed via an enzymatic method and high-performance liquid chromatography, respectively. A noncompartmental approach was used for pharmacokinetic analysis. Pharmacokinetic variables were compared via a Bland-Altman plot and an ANOVA. Results-Compared with results for creatinine, iohexol had a significantly higher mean SD plasma clearance (3.4 +/- 0.8 mL/min/kg vs 3.0 +/- 0.7 mL/min/kg) and a significantly lower mean volume of distribution at steady state (250 +/- 37 mL/kg vs 539 +/- 73 mL/kg), mean residence time (80 +/- 31 minutes vs 195 73 minutes), and mean elimination half-life (74 +/- 20 minutes vs 173 +/- 53 minutes). Despite discrepancies between clearances, especially for high values, the difference was < 0.6 mL/min/kg for 34 (68%) dogs. Three dogs with a low GFR (< 2 mL/min/kg) were classified similarly by both methods. Conclusions and Clinical Relevance-Plasma iohexol and creatinine clearances can be used interchangeably for screening patients suspected of having chronic kidney disease fie, low GFR), but large differences may exist for dogs with a GFR within or above the reference range. (Am J Vet Res 2012;73:1841-1847)