Objective: The present study was aimed to determine effect of seizure control to Therapeutic drug monitoring [TDM] of
antiepileptic drugs [AEDs].
Materials and Methods: The retrospective study was performed in outpatients who were attending the Epilepsy Clinic at Srinagarind Hospital, Khon Kaen University in 2011. The patients who were aged 15 or over, had enrolled in the Epilepsy Clinic for a minimum of 3 months and been treated with at least one AED were included into the study. The follow-up time was one year. Data on seizure control and TDM was collected from chart reviews and an electronic database. Data analysis was performed by using univariate analysis in SPSS 11.
Results: 382 patients received medical care at the clinic at a total of 2,369 times. Their average age was 40.35+0.83 years. Most (51.05%) were females. The average age epilepsy started to develop in the patients was 30.87+1.04 years, the average treatment period was 8.55+0.46 years with an average of 2.55+1.11 years of treatment in this clinic. The most common epileptic type was generalized tonic clonic seizure (59.42%), complex partial seizure (41.36%), and simple partial seizure (10.47%). The average number of seizures was 7.46+0.69 times/month. The percentage of seizure free was 55.54%. The drugs mostly used were Phenytoin (43.98%) and sodium valproate (40.44%). Therapeutic drug monitoring was carried out 185 times per 2369 clinical visits (7.81%). The indication of TDM requests were suspected sub-therapeutic level 79 times (41.80%), routine follow-up 75 times (39.68%), suspected toxicity 34 times (17.99%) and confirming drug level 1 time (0.53%). Plasma drug Concentrations appeared to be within therapeutic level 134 times (50.19%), sub-therapeutic level 69 times (25.84%), and over therapeutic level 64 times (23.97%). TDM requests was found to be significantly increasing in patients with uncontrolled seizure (p<0.05).
Conclusion: TDM is the necessary approach in helping multi-disciplinary team to manage use of medications appropriately.

Keywords: Therapeutic drug monitoring, TDM, Antiepileptic drug, Epilepsy