Evaluation of the Appropriateness of Antiepileptic Drug Level Monitoring

Lee, Soo Youn; Kim, Jong Won

Abstract

BACKGROUND
Therapeutic drug monitoring (TDM) of antiepileptic drugs (AED) is an essential component of the management of epilepsy. But in clinical practice, the questions about the appropriateness of TDM of AED are remained. We performed the present study to evaluate the appropriateness of TDM of AED and pursued for the improvement of the clinical value of TDM.
METHODS
A retrospective study of 1,302 cases of TDM of 4 AED including phenytoin, carbamazepine, valproic acid and phenobarbital from 304 patients was conducted at Samsung Medical Center from March 1 to April 30, 1998. We reviewed the medical records and collected all variables such as clinical characteristics of patients, drug regimen, indication of TDM, sampling time, serum drug concentration, and changes in management following TDM. The set of criteria for evaluating the rational indication and sampling was applied.
RESULTS
TDM of AED constitute 52.3% of all TDM performed. We found 76.7% of cases had inappropriate indication or incorrect sampling. Most inappropriate measurements were part of a series of repeated determinations after starting or changing the drug regimen but before a steady state had been achieved. Median interval between two measurements in in- and out-patients were 24.3 hours and 340.2 hours, respectively. Serum concentrations of phenytoin were less likely to fall within the therapeutic range. The result of TDM led to alterations in management in 20.1% of all cases. Both increases and decreases were observed to follow low, target and high concentrations.
CONCLUSIONS
TDM of AED is frequently done inappropriately in the current TDM practice. Therefore, providing appropriate guidelines, persistent education, and interpretative reporting for individualized dosage adjustment are needed. The establishment of a comprehensive TDM service can improve the rational use of TDM of AED.