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

Background: 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 (U8h) 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 (CrClCG) versus 8-h CrCl (CrCl8h). Methods: This was an observational, retrospective cohort study of adult patients admitted between March 2018 and September 2018 with a collection U8h during hospitalization. The primary outcome was discordance of renal drug dosing defined as the percentage of U8h for which at least one different active medication CrCl dosing cutoff would result using the CrClCG versus CrCl8h. The secondary outcomes were correlation between CrClCG and CrCl8h and percentage of CrClCG values outside ± 20% of the CrCl8h. Results: 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 collection8h. Median CrCl8h was 86.2 (43.5–140.3) mL/min versus 99.7 (56.5–166.9) mL/min CrClCG(P < 0.001) and discordance was 25%. The correlation between CrCl8h and CrClCG was 0.76 (P < 0.001). Only 31% of CrClCG values were within ± 20% of the CrCl8h value. Conclusion: We found 25% discordance for drug dosing between CrCl8h and CrClCG. Further studies are needed to determine the impact on clinical outcomes.