Functional range of creatinine clearance for renal drug dosing: a practical solution to the controversy of which weight to use in the Cockcroft-Gault equation.

OBJECTIVE: To describe a practical solution for addressing body weight when using the Cockcroft-Gault equation to determine drug dosing. DATA SOURCES: A literature search was conducted using PubMed MEDLINE (1980-April 2013) using creatinine clearance, Cockcroft and Gault, Cockcroft-Gault, body weight, and obesity as search terms. Reference citations from publications reviewed were included. STUDY SELECTION AND DATA EXTRACTION: All English-language articles identified by the search were reviewed. Studies comparing the accuracy and bias of the Cockcroft-Gault equation using a variety of body weight designations in adult populations were included in the analysis. DATA SYNTHESIS: Study results indicated that, for obese patients, ideal body weight (IBW) underestimates creatinine clearance (CrCl) and total body weight (TBW) overestimates CrCl. Some studies suggest that adjusted body weight with a factor of 0.4 is most accurate, while others suggest the use of lean body weight. These studies have failed to produce a definitive resolution to the controversy. Despite many well-designed studies, the Cockcroft-Gault body weight controversy remains unresolved and uncertainty continues to exist as to which form of weight should be used in the equation. A different perspective is warranted. Since renal dosing guidelines are generally based on ranges of CrCl, applying a CrCl range to describe a patient's renal function might be more practical than relying on a specific CrCl value. Ultimately, CrCl-based drug dosing involves the use of an imperfect mathematical approximation, which is then applied as precisely as possible to the benefit versus risk analysis for a specific patient. CONCLUSIONS: We propose the use of a CrCl range for drug dosing purposes, with the lower boundary defined by using IBW in the Cockcroft-Gault equation and the upper boundary by using TBW.