Determination of Creatinine Clearance by Vancomycin Levels as Compared to Cockcroft-Gault Equation

Introduction: Estimation of the glomerular filtration rate using creatinine clearance as calculated by the Cockcroft-Gault (CG) equation is the standard for determining drug dosing in hospitalized patients. The CG equation has been studied to have limitations and may be inaccurate in the critically ill population. The goal of this study is to describe the differences in creatinine clearance as calculated by the Cockcroft-Gault equation versus determination of the creatinine clearance using vancomycin pharmacokinetic parameters.


Methods: A retrospective analysis of patients admitted to an intensive care unit at Corewell Health East William Beaumont Hospital and were evaluated by the pharmacy vancomycin dosing service. Patients that received vancomycin and two levels were obtained for area under the serum concentration/time curve for a 24-hour interval above the MIC calculation were included in the analysis. Creatinine calculations for these patients were determined and compared to the use of the CG equation for estimating creatinine clearance.


Results: Of the 488 patients identified who were admitted to an intensive care unit who received vancomycin from January 3, 2024, to June 1, 2025, a convenience sample of 64 patients were included in the analysis. The cohort was mostly male (59.4%) versus female (46.1%). The average age of the patients was 60 years old and the range from 18-93 years old. The range of creatinine clearances calculated by the CG equation was 33 mL/min to 343 mL/min. The range of creatinine clearances calculated using vancomycin kinetics was 6.9 mL/min to 301 mL/min. The average CG creatinine clearance was 123 mL/min compared to the average vancomycin clearance using vancomycin kinetics was 87.1 mL/min.


Conclusions: Compared to creatinine clearance calculated by the CG equation, using vancomycin kinetics to calculate a creatinine clearance led to an observed decrease in the creatinine clearance which would lead to a decrease in the estimation of glomerular filtration rate. These critically ill patients may have an estimated glomerular filtration rate lower than what is calculated with the CG equation, leading to inappropriate dosage regimens resulting in toxicity.