Effect of discrepancy in estimated renal function on vancomycin area under the blood concentration-time curve: a retrospective cohort study comparing serum creatinine and serum cystatin C.

Abstract

Background: Accurate estimation of renal function is essential for determining vancomycin (VCM) dosing. Serum creatinine (sCr)-based formulas are used to estimate renal function; however, they may overestimate the glomerular filtration rate (GFR) in patients with reduced muscle mass. Serum cystatin C (cys-C) may provide more accurate estimates of renal function in such populations.

Aim: We aimed to investigate the effect of estimated GFR (eGFR) discordance on area under the blood concentration-time curve (AUC) of VCM.

Method: Data from 118 patients with simultaneous sCr and cys-C data available at start of VCM therapy were analyzed. Patients were classified into eGFR discordance and concordance groups. eGFR discordance was defined as a case where the sCr-based eGFR was 30% or higher than the cys-C-based eGFR. The primary outcome was the association between eGFR discordance and upward deviation of the VCM AUC.

Results: Seventy-two patients with eGFR discordance had significantly higher measurement of VCM AUC than predicted (p < 0.001). Multivariate logistic regression analysis identified age, hospital stay of ≥ 12 days, and eGFR discordance as significant predictors of AUC upward deviation. Factors associated with discordance in the eGFR included these risk factors and intensive care unit (ICU) stay.

Conclusion: This study highlights the importance of measuring cys-C levels at initiation of VCM therapy identifying patients at risk of renal function overestimation and subsequent VCM overdosing. Older with extended hospitalization or ICU stay may benefit from measuring cys-C levels of optimize VCM therapy and reduce drug-induced toxicity risk.