Abstract
Background: This study aims to determine and compare phenytoin concentrations in cerebrospinal fluid (CSF), serum, and urine. In addition, it strives to investigate their inter-correlations to provide insight into alternative monitoring methods.
Methods: This study was conducted on 16 traumatic brain injury (TBI) patients admitted to the intensive care unit. Phenytoin concentrations were measured in CSF, serum, and urine samples using a liquid chromatography-tandem mass spectrometry. Statistical analysis assessed correlations between phenytoin levels across different samples and between concentrations and the received daily dose, age, and body mass index (BMI).
Results: Phenytoin concentrations varied significantly between CSF, serum, and urine, with serum levels being the highest. Correlation analyses revealed significant positive correlations between phenytoin CSF and serum levels (r=0.83, P=0.0005), serum and urine levels (r=0.73, P=0.003), and CSF and urine levels (r=0.64, P=0.013). Serum concentrations were not influenced by age or BMI. No significant correlation was observed between phenytoin levels and its daily dose.
Conclusion: This study demonstrated significant correlations between phenytoin levels in CSF and serum, suggesting that CSF could be a viable alternative for therapeutic drug monitoring (TDM) in TBI patients. However, urine concentrations were less reliable. Further studies with larger patient cohorts and different clinical settings are needed to validate these findings and explore the potential of CSF monitoring in routine clinical practice.