Associations Between Therapeutic Drug Monitoring Indications and Plasma Concentrations in Epilepsy Management: Insights from a Tertiary Care Hospital

Background Epilepsy affects around 70 million people worldwide, with a higher prevalence in developing countries like Malaysia. Antiepileptic drugs (AEDs) such as carbamazepine, phenobarbitone, valproic acid, and phenytoin are essential for managing epilepsy, but their pharmacokinetic variability requires precise monitoring. Limited local data underscore the need to optimize therapeutic drug monitoring (TDM) practices in Malaysia to improve therapeutic outcomes. Purpose This study evaluates the associations between TDM indications (breakthrough seizure, dosing adequacy, compliance, and suspected toxicity) and plasma concentrations of four commonly used AEDs to guide drug therapy in epilepsy management. Materials and Methods A retrospective, case-control study was conducted over 1 year in a tertiary care hospital, including patients on AEDs requiring TDM. Plasma drug levels were analyzed in relation to breakthrough seizures, dosing adequacy, compliance, and suspected toxicity. Statistical analysis was performed using SPSS, focusing on descriptive statistics and odds ratios with 95% confidence intervals. Results A total of 780 samples were analyzed, revealing significant variations in plasma concentrations of AEDs relative to TDM indications. Carbamazepine had the highest proportion within the therapeutic range (78.9%), followed by phenobarbitone (61.3%). Valproic acid and phenytoin had lower therapeutic range proportions (40.6% and 18.1%, respectively). Non-compliance with carbamazepine impacted outcomes, while phenytoin and valproic acid were strongly linked to toxicity. Conclusion The study emphasizes the importance of TDM in epilepsy management, particularly for optimizing dosages and monitoring compliance and toxicity. It suggests that Malaysian TDM guidelines should focus on more frequent monitoring of AEDs like phenytoin and valproic acid, which show higher rates of sub-therapeutic and toxic levels. These insights could improve AED therapy and patient care in Malaysia.