In this study, a clinical trial was conducted to develop a population PK model for cefepime in critically ill patients assessing renal and non-renal clearance separately, based on both plasma and urinary cefepime concentrations. This model then served as a tool to compare the adequacy of six different renal markers as predictors for renal cefepime clearance. After integrating the most adequate predictor into the PK model, the final model was used to evaluate current dose recommendations for cefepime.