Comparison of kinetic and standard formulas for estimating glomerular filtration rate in acute kidney injury: implications for antibiotic dosing, a prospective study.

PURPOSE

Acute kidney injury (AKI) is a prevalent complication in critically care, affecting prognosis and management. Standard formulas for estimating glomerular filtration rate (GFR), such as CKD-EPI and MDRD, are frequently used; accuracy in AKI is limited due to fluctuating creatinine. This study aimed to evaluate the agreement between standard GFR and kinetic-GFR formulas in AKI patients and to assess the impact on antibiotic dosing.

METHODS

In this prospective, observational study conducted at Erciyes University Hospital, 100 patients with AKI were enrolled. GFR was estimated using CKD-EPI, MDRD, and kinetic-GFR formulas, including volume-adjusted kinetic formulas. Agreement between formulas was analyzed using Kappa coefficient.

RESULTS

Statistically significant but imperfect agreement was observed between kinetic and standard formulas (CKD-EPI: κ = 0.592 ± 0.026, p < 0.001; MDRD: κ = 0.649 ± 0.025, p < 0.001). Approximately 28-30% of follow-up days revealed category mismatches between standard and kinetic formulas. 47% of the mismatches of CKD-EPI vs ki-CKD-EPI, and 31% for MDRD vs ki-MDRD occurred on day 2. Volume-adjusted kinetic formulas increased the mismatch rate, with CKD-EPI increasing from 28.5% to 30.6% (p < 0.001) and MDRD from 24.4% to 27.2% (p < 0.001). Significant dose adjustments were required when kinetic-GFR was used, particularly for nephrotoxic antibiotics.

CONCLUSION

The use of kinetic-GFR formulas improves the accuracy of GFR estimation in AKI, especially in the early stages, and may lead to more appropriate antibiotic dosing. However, further studies are needed to fully understand the clinical implications, especially regarding drug levels and patient outcomes.