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Objective: To compare the proportions of appropriate TDM utilization regarding the indication, sampling time, and application of the measured drug levels of antiepileptic drugs (AEDs) between the pre-intervention period and pharmacist intervention period., Material and Method: The baseline evaluation and pharmacist intervention study of TDM use for phenytoin, carbamazepine, or valproic acid were conducted at a medical teaching hospital in Southern Thailand. TDM requests, interpretation and dosage adjustment recommendations were mainly responsible by residents. In the intervention period, each of the three-step TDM process was assessed by the pharmacist for appropriateness and a suggestion provided if necessary prior to a final recommendation made by the resident. The criteria for appropriateness of TDM for AEDs were developed and validated by two neurologists. The present study included 44 TDM tests (22 patients) during the baseline period and 43 tests (27 patients) during the intervention period. The proportions of appropriate TDM utilization between the two periods were compared using Chi-square test., Results: In the baseline period, proportions of appropriately performed TDM were: indication (63.6%), sampling time (47.7%), and application of drug levels (63.6%). Pharmacist intervention significantly increased the proportions of appropriate indication (97.7%, p = 0.001), sampling time (79.1, p = 0.0023), and applications (83.7%, p = 0.0293). There were 12 tests (27.3%) and 29 tests (67.4%) (p = 0.0001) during the baseline and the intervention period, respectively, that met all 3 criteria of appropriate TDM use. Sixteen requests without indication found in the baseline period was reduced to one in the intervention period, and thus reduced the unnecessary cost by 90%. Of 59 steady-state drug levels, 34 (57.6%, p = 0.0005) significantly correlated with clinical responses., Conclusion: Pharmacist intervention significantly improved appropriateness of TDM use, and substantially reduced unnecessary costs. Using a screening checklist including the indication, sampling time and data needed for proper interpretation of the results can help improve the appropriateness of TDM utilization.