Risk stratification of AUC upward deviation in patients with low serum creatinine levels treated with vancomycin: a multicenter retrospective study.

Introduction: In patients with diminished muscle mass, serum creatinine (SCr) levels may be misleadingly low, potentially leading to overestimations of kidney function and unexpectedly high blood levels of vancomycin. This study aimed to identify factors contributing to this discrepancy and develop a flowchart for stratifying the risk of excessive vancomycin exposure, measured as an upward deviation in the area under the concentration-time curve (AUC) in patients with low SCr levels.

Methods: We analyzed data from patients who received vancomycin and had an SCr value <0.6 mg/dL. The discrepancy between the AUC24-48 h initial dosing and AUC24-48 h TDM was calculated; a ratio (AUC24-48 h TDM/AUC24-48 h initial dosing) higher than 1.2 defined an upward deviation in the AUC. A decision tree model was constructed using classification and regression tree algorithms.

Results: Among the 95 patients (median age [interquartile range], 69 [58, 80] years; 68% female), the upward AUC deviation was 40% (38/95). Three factors (creatinine clearance: 115 ml/min, age: 69 years, and blood urea nitrogen/SCr: 17) were selected for the decision flowchart and included in four subgroups.

Conclusion: We developed a flowchart to identify patients with low SCr levels whose AUC at therapeutic drug monitoring deviated upward by >20% from the predicted AUC.