What Makes Epilepsy Drug Refractory?

About 20-40% of patients with epilepsy will be refractory to medical treatment with antiepileptic drugs. It is unclear whether patients are already drug-resistant at the time of their initial presentation, or whether they become so over the course of their illness. Identifying predictors for drug-refractory epilepsy may be important for directing epilepsy patients to an effective nonpharmacological treatment, such as surgery or the vagus nerve stimulator, in a timely manner. In addition, understanding the factors that lead to the drug-refractory state may facilitate the development of new therapies that are effective in the resistant subgroup. This paper identifies various predictors that have been associated with drug-refractory epilepsy, discusses the evidence behind each factor and recommends strategies for clarifying predictors of refractoriness.