Monitoring of tobramycin serum concentrations in selected critically ill patients receiving selective decontamination of the digestive tract: a retrospective evaluation.

INTRODUCTION: Selective decontamination of the digestive tract (SDD) is a strategy in mechanically ventilated patients to reduce mortality. Treatment consists of enterally administered non-absorbable antibiotics, i.e., tobramycin. However, most intensive care unit (ICU) patients with SDD appear to have detectable tobramycin serum concentrations. The Rijnstate Hospital implemented a protocol for therapeutic drug monitoring (TDM) of tobramycin in patients at risk. The aim of this study was to evaluate the necessity of TDM in these patients and to optimize the current protocol.

METHODS: This retrospective observational study included ICU patients with SDD treatment for ≥ 7 days and renal failure. These patients were considered eligible for monitoring of tobramycin. Tobramycin serum concentrations, relevant laboratory parameters (i.e., renal function, lactate), and patient data were extracted from the National Intensive Care Evaluation database and the hospital electronic patient data system.

RESULTS: In 23 subjects, a total of 43 tobramycin serum concentrations was determined. The median tobramycin serum concentration was 0.33 (IQR 0.17-0.49) mg/L of which 12 (27.9%) samples had concentrations < 0.2 mg/L, 30 (69.8%) had concentrations 0.2-1.0 mg/L and 1 (2.3%) had a toxic concentration > 1.0 mg/L. In 3 (7.0%) cases, an intervention was conducted based on the tobramycin serum concentration.

CONCLUSION: The majority (83.7%) of samples had detectable tobramycin serum concentrations. Monitoring of tobramycin serum concentrations can be considered necessary in patients at risk. However, the current protocol should be optimized to intercept patients more precise.