Disagreement in Estimates of Kidney Function for Drug Dosing in Obese Inpatients.

Background: The Cockcroft-Gault (CG), Modification of Diet in Renal Disease (MDRD), and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations are used to estimate kidney function. However, utility has been questioned in the obese population. Objective: To evaluate differences in estimates of kidney function in obese patients and implications for drug dosing. Methods: This was a retrospective study of adult inpatients with a body mass index >= 30 kg/m(2) and stable kidney function. Patients were categorized based on creatinine clearance (CrCl): group 1-CrCl >= 60 mL/min and group 2-CrCl 15 to 59 mL/min. Mean estimates of kidney function and recommended doses of 8 renally eliminated medications were compared. Results: For the 166 patients included, mean estimates using CG, MDRD, and CKD-EPI for group 1 were 87 (23) mL/min, 91 (21) mL/min, and 96 (23) mL/min, respectively. Group 2 estimates were 42 (13) mL/min, 51 (15) mL/min, and 51 (16) mL/min, respectively. MDRD and CKD-EPI estimates were significantly higher than CG in 125 (75%) and 140 (84%) patients, respectively. Dose discrepancies were most often due to higher dose recommendations using MDRD or CKD-EPI compared to CG. Conclusion: Careful consideration of the method used to estimate kidney function, the method used for developing dosing recommendations, and the risk-benefit profile is warranted when designing drug regimens in obese individuals.