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.

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.