Application of an isocratic methanol-based HPLC method for the determination of iohexol concentrations and glomerular filtration rate in patients with cirrhosis

Abstract

Background: Glomerular filtration rate (GFR) and mortality is more accurately determined by gold standard measures than serum creatinine-based estimates in cirrhosis. No formal validation of any gold standard method has been reported. Methods: An isocratic methanol-based method incorporating the reference standard iohexol-related compound C was developed and validated in 12 patients with cirrhosis by simultaneously determining GFR using iohexol and chromium-51 labelled ethylenediamine tetraacetic acid (51Cr-EDTA) clearance. Iohexol pharmacokinetics was also studied with the collection of blood and ascitic fluid at intervals following an iohexol bolus. Results: Triplicate assays produced a linear calibration curve (R2 = 0.99, N = 5) over an iohexol concentration range of 23.6-755 μg/L. Mean (range) extraction recovery of iohexol from serum was greater than 95% (94-97%), with an intraday coefficient of variation less than 3%. Twelve patients with cirrhosis with mean Child-Pugh score of 9 displayed a mean difference (bias) -1.3 mL/min/1.73 m2 (-18 to +16) comparing iohexol with 51Cr-EDTA. Iohexol equilibrated between blood and ascitic compartments after 4 h. Conclusion: A simple, cheap, and accurate isocratic, methanol-based method for the determination of iohexol concentrations is described, validated according to Food and Drug Administration guidance. Iohexol demonstrated comparable performance with 51Cr-EDTA in determining GFR. Delayed equilibrium of iohexol between blood and ascitic compartments suggests sampling beyond 4 h would improve accuracy of GFR determinations in patients with cirrhosis. © The Author(s) 2013.