Differentiating True Nephrotoxicity From Pseudo-nephrotoxicity: A Prospective Comparative Study of Vancomycin Plus Piperacillin-Tazobactam vs. Meropenem Using Serum Creatinine and Cystatin-C

Vancomycin is commonly administered in combination with broad-spectrum beta-lactam antibiotics for empiric treatment of serious infections. Several studies have reported a higher incidence of nephrotoxicity in patients receiving vancomycin plus piperacillin-tazobactam compared with vancomycin combined with other antipseudomonal beta-lactams. However, most of these studies have defined kidney injury using serum creatinine alone. This has raised concern that the observed increase in nephrotoxicity may, at least in part, represent pseudo-nephrotoxicity caused by an increase in serum creatinine without a corresponding reduction in true kidney function.

This prospective, non-interventional, comparative two-arm cohort study will evaluate adult patients receiving vancomycin in combination with either piperacillin-tazobactam or meropenem. Treatment selection, antimicrobial dosing, vancomycin therapeutic drug monitoring, fluid management, hemodynamic management, and other clinical decisions will remain under the responsibility of the treating clinical team and will not be determined by the study investigators.

The primary objective is to compare the incidence of true nephrotoxicity between the two treatment groups. Kidney function will be assessed prospectively using both serum creatinine and cystatin C. True nephrotoxicity will be defined as fulfillment of the study criteria for acute kidney injury using both serum creatinine and cystatin C, whereas pseudo-nephrotoxicity will be defined as serum creatinine-based acute kidney injury without a corresponding increase in cystatin C.

Serum creatinine and cystatin C will be assessed at baseline and serially during combination antimicrobial therapy, with additional follow-up measurements after discontinuation when available according to the study protocol. This simultaneous biomarker assessment is intended to help distinguish functional changes in serum creatinine from kidney injury supported by a parallel change in cystatin C.

Secondary assessments will include the time to onset of acute kidney injury based separately on serum creatinine and cystatin C, the incidence of transient and persistent acute kidney injury, kidney recovery, and the severity of acute kidney injury. Kidney recovery and progression to acute kidney disease will also be assessed during follow-up when applicable.

Patients will be categorized into two observational exposure groups according to the beta-lactam prescribed by the treating team: vancomycin plus piperacillin-tazobactam or vancomycin plus meropenem. Relevant demographic, clinical, laboratory, antimicrobial exposure, and potential nephrotoxic risk factors will be prospectively collected.

The study is designed to clarify whether the higher incidence of nephrotoxicity reported with vancomycin plus piperacillin-tazobactam represents true renal injury or predominantly a serum creatinine-based phenomenon. The findings may improve interpretation of kidney function during antibiotic therapy and may help clinicians balance antimicrobial coverage with the risk of nephrotoxicity when selecting empiric antibiotic regimens.