Evaluation of iohexol clearance used to estimate glomerular filtration rate in clinically normal foals

Kathleen C. Gonda Department of Large Animal Clinical Science, Virginia-Maryland Regional College of Veterinary Medicine, Blacksburg, VA 24060.

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 DVM, MS
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Jeff R. Wilcke Department of Biomedical Sciences and Pathobiology, Virginia-Maryland Regional College of Veterinary Medicine, Blacksburg, VA 24060.

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Mark V. Crisman Department of Large Animal Clinical Science, Virginia-Maryland Regional College of Veterinary Medicine, Blacksburg, VA 24060.

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Daniel L. Ward Office of Research and Graduate Studies, Virginia-Maryland Regional College of Veterinary Medicine, Blacksburg, VA 24060.

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John L. Robertson Department of Biomedical Sciences and Pathobiology, Virginia-Maryland Regional College of Veterinary Medicine, Blacksburg, VA 24060.

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Delmar R. Finco Department of Physiology and Pharmacology, College of Veterinary Medicine, The University of Georgia, Athens, GA 30602.

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W. Emmett Braselton Department of Pharmacology and Toxicology, Animal Health Diagnostic Laboratory, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824.

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Abstract

Objective—To determine whether pharmacokinetic analysis of data derived from a single IV dose of iohexol could be used to predict creatinine clearance and evaluate simplified methods for predicting serum clearance of iohexol with data derived from 2 or 3 blood samples in clinically normal foals.

Animals—10 healthy foals.

Procedure—Serum disposition of iohexol and exogenous creatinine clearance was determined simultaneously in each foal (5 males and 5 females). A 3-compartment model of iohexol serum disposition was selected via standard methods. Iohexol clearance calculated from the model was compared with creatinine clearance. Separate limited-sample models were created with various combinations of sample times from the terminal slope of the plasma versus time profile for iohexol. Correction factors were determined for the limited-sample models, and iohexol clearance calculated via each method was compared with exogenous creatinine clearance by use of method comparison techniques.

Results—Mean exogenous creatinine clearance was 2.17 mL/min/kg. The disposition of iohexol was best described by a 3-compartment open model. Mean clearance value for iohexol was 2.15 mL/min/kg and was not significantly different from mean creatinine clearance. A method for predicting serum iohexol clearance based on a 2-sample protocol (3- and 4-hour samples) was developed.

Conclusions and Clinical Relevance—Iohexol clearance can be used to predict exogenous creatinine clearance and can be determined from 2 blood samples taken after IV injection of iohexol. Appropriate correction factors for adult horses and horses with abnormal glomerular filtration rate need to be determined. (Am J Vet Res 2003;64:1486–1490)

Abstract

Objective—To determine whether pharmacokinetic analysis of data derived from a single IV dose of iohexol could be used to predict creatinine clearance and evaluate simplified methods for predicting serum clearance of iohexol with data derived from 2 or 3 blood samples in clinically normal foals.

Animals—10 healthy foals.

Procedure—Serum disposition of iohexol and exogenous creatinine clearance was determined simultaneously in each foal (5 males and 5 females). A 3-compartment model of iohexol serum disposition was selected via standard methods. Iohexol clearance calculated from the model was compared with creatinine clearance. Separate limited-sample models were created with various combinations of sample times from the terminal slope of the plasma versus time profile for iohexol. Correction factors were determined for the limited-sample models, and iohexol clearance calculated via each method was compared with exogenous creatinine clearance by use of method comparison techniques.

Results—Mean exogenous creatinine clearance was 2.17 mL/min/kg. The disposition of iohexol was best described by a 3-compartment open model. Mean clearance value for iohexol was 2.15 mL/min/kg and was not significantly different from mean creatinine clearance. A method for predicting serum iohexol clearance based on a 2-sample protocol (3- and 4-hour samples) was developed.

Conclusions and Clinical Relevance—Iohexol clearance can be used to predict exogenous creatinine clearance and can be determined from 2 blood samples taken after IV injection of iohexol. Appropriate correction factors for adult horses and horses with abnormal glomerular filtration rate need to be determined. (Am J Vet Res 2003;64:1486–1490)

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