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