Therapeutic drug monitoring of antiepileptic drugs in the West Bank, Palestine: a 25-year retrospective cohort study from a multi-branch laboratory network

Background Therapeutic drug monitoring (TDM) of antiepileptic drugs (AEDs) is essential for optimizing seizure control while minimizing toxicity, particularly in resource-constrained settings. Palestine’s West Bank healthcare system operates under profound geopolitical and infrastructural constraints. This study presents the first large-scale, multi-decade retrospective analysis of AED TDM patterns from a Palestinian multi-branch laboratory network. Methods A retrospective cohort study was conducted using 9,232 individual AED serum level measurements from 5,197 unique patients recorded in the Laboratory Information System of Medicare Laboratories (33 branches, West Bank) from 2001 to 2026. Six AEDs were evaluated: carbamazepine, levetiracetam, lamotrigine, phenobarbital, phenytoin, and valproic acid. Results were classified as sub-therapeutic, therapeutic, or toxic against established reference ranges. Results Of 9,232 measurements, 53.4% were therapeutic, 40.4% sub-therapeutic, and 6.1% toxic. Phenytoin showed the worst therapeutic control (31.0% therapeutic; median 8.4 mcg/mL). Valproic acid exhibited a 47.8% sub-therapeutic rate despite the highest test volume ( n = 4,021). Lamotrigine had the highest toxic proportion (25.9%). Levetiracetam demonstrated the best control (88.6% therapeutic). Testing volume increased approximately 5.7-fold over the 25-year period. Conclusions Frequent out-of-range AED levels, particularly for phenytoin and valproic acid, reflect complex pharmacokinetic and systemic challenges in the West Bank. The overall sub-therapeutic rate (40.4%) highlights the urgent need for enhanced TDM programs, improved patient adherence strategies, and strengthened pharmaceutical care infrastructure in this conflict-affected region.