Estimating GFR Using Creatinine, Cystatin C, or Both and the Impact on Predicted Vancomycin Half-Life

Area of Science:

• Nephrology
• Pharmacokinetics
• Critical Care Medicine

Background:

• Glomerular filtration rate (GFR) estimation is crucial for drug dosing, commonly using creatinine, cystatin C, or combined equations.
• Discrepancies in GFR estimations can lead to significant variations in drug dosage adjustments.

Purpose of the Study:

• To compare GFR estimations from four common equations: Cockcroft-Gault (CrClCG), CKD-EPI Creatinine (eGFRcr), CKD-EPI Cystatin C (eGFRcys), and CKD-EPI Creatinine-Cystatin (eGFRcr-cys).
• To evaluate the correlation between these GFR estimations.
• To determine the impact of varying GFR estimates on predicted vancomycin half-life (t1/2).

Main Methods:

• Retrospective cohort study of critically ill adults.
• GFR estimated using CrClCG, eGFRcr, eGFRcys, and eGFRcr-cys.
• Statistical analyses included MANOVA and Pearson correlation coefficient (r2).
• Bayesian modeling predicted vancomycin t1/2.

Main Results:

• Significant differences in mean GFRs across the four equations (P < 0.0001).
• Moderate to strong correlations (r2 values ranging from 0.54 to 0.92) observed between equations.
• Substantial variations in predicted vancomycin t1/2 (ranging from 33.3 to 43.2 hours) based on GFR estimation method.
• Discrepancies were more pronounced at higher GFRs.

Conclusions:

• GFR estimation methods yield substantially different results, particularly creatinine-based equations yielding higher values.
• These GFR discrepancies lead to significant differences in predicted vancomycin half-life.
• Awareness of GFR estimation method variability is essential for accurate vancomycin dosing and clinical decision-making.