OBJECTIVE: The objective of this study was to determine the relationship between the plasma polymyxin B concentration and renal function in elderly patients. METHODS: This prospective, case-control, observational study included elderly patients who received polymyxin B therapy and were divided into an acute kidney injury (AKI) group and a non-AKI group based on their renal function. We monitored the pharmacokinetics and pharmacodynamics of polymyxin B, including the minimum plasma concentration (C RESULTS: The loading doses, C CONCLUSION: Monitoring plasma polymyxin B concentrations is essential in elderly patients. Keeping the C