Discordance of renal drug dosing using estimated creatinine clearance and measured urine creatinine clearance in hospitalized adults: A retrospective cohort study

Assessment of kidney function is fundamental to optimize drug dosing. The Cockcroft-Gault (CG) equation is widely used but has questionable validity for females, changing renal function, and the critical ill. Eight-hour urine collections (U ) offer direct measurement of creatinine clearance (CrCl) but lack the data for drug dosing. The primary objective of this study was to determine if there was a difference in renal drug dosing based on the estimation of CG CrCl (CrCl ) versus 8-h CrCl (CrCl ). This was an observational, retrospective cohort study of adult patients admitted between March 2018 and September 2018 with a collection U during hospitalization. The primary outcome was discordance of renal drug dosing defined as the percentage of U for which at least one different active medication CrCl dosing cutoff would result using the CrCl versus CrCl . The secondary outcomes were correlation between CrCl and CrCl and percentage of CrCl values outside ± 20% of the CrCl . One hundred collections drawn from 85 unique patients (50.6% male, median age 55 [41-70] years, intensive care unit 88%) were included in the analysis. Median serum creatinine was 0.76 (0.52-1.06) mg/dL and blood urea nitrogen was 20 (14-28) mg/dL at time of collection . Median CrCl was 86.2 (43.5-140.3) mL/min versus 99.7 (56.5-166.9) mL/min CrCl ( < 0.001) and discordance was 25%. The correlation between CrCl and CrCl was 0.76 ( < 0.001). Only 31% of CrCl values were within ± 20% of the CrCl value. We found 25% discordance for drug dosing between CrCl and CrCl Further studies are needed to determine the impact on clinical outcomes.