Background: Since the derivation of the Modification of Diet in Renal Disease (MDRD) equation for estimating glomerular filtration rate (GFR), investigators determined that it cannot be used for drug dosing. In 2009, the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) derived an equation that was more accurate than the MDRD estimation of GFR. Therefore, questions exist about which method should be preferred in making dosage adjustments for renally eliminated antimicrobials.
Objective: To determine whether a difference exists when making antimicrobial dosage adjustments in patients with CKD based on estimation of GFR using the CKD-EPI and Cockcroft-Gault equations.
Methods: A database of 409 patients with CKD admitted to a tertiary care facility was used. GFR was calculated using both the CKD-EPI equation(s) and the Cockcroft-Gault equation and compared using correlation and Bland-Altman methodology. Dosage discordance rates of antimicrobials were determined.
Results: Average GFRs for all patients using the Cockcroft-Gault and CKD-EPI equations were 34.8 +/- 12 mL/min and 39.9 +/- 13 mL/min, respectively (5.09 [95% CI 4.60 to 5.59]; p < 0.001). The correlation coefficient between the 2 estimations was high (r = 0.91). The Bland-Altman plot yielded limits of agreement of 15.3 and -5.1; thus, the CKD-EPI estimation may range from 5.1 mL/min below to 15.3 mL/min above the Cockcroft-Gault estimation for 95% of the cases. A discordance rate of 15-25% existed among the recommended dosing adjustments of the selected antimicrobials when comparing the Cockcroft-Gault and CKD-EPI estimations.
Conclusions: Though this study did not determine which equation should be selected to dose adjust antimicrobials, it demonstrated statistically significant differences between the Cockcroft-Gault and CKD-EPI equations. The clinical significance of these differences is uncertain in the absence of data assessing clinical outcomes that result from the use of the discordant doses. Clinical judgment should be employed when making renal dosage adjustments of antimicrobials.