Recognizing Drug-Resistant Epilepsy and Timing the Referral

Key Takeaways:

• Drug-resistant epilepsy is defined as failure of 2 adequate, tolerated antiseizure medication regimens to achieve sustained seizure freedom, a threshold reached by roughly one-third of patients.
• The likelihood of seizure freedom falls sharply after 2 appropriate medications have failed, making repeated medication changes without comprehensive re-evaluation increasingly unlikely to achieve sustained seizure freedom.
• Meeting the 2-drug threshold should prompt referral to a comprehensive epilepsy center for re-evaluation.

Roughly one-third of people with epilepsy do not achieve lasting seizure control on medication, a proportion that has not shifted appreciably despite the introduction of many new antiseizure medications (ASMs). Recognizing this group early matters because persistent seizures are associated with increased risks of injury, hospitalization, cognitive consequences, reduced quality of life, and premature mortality. The patients who remain uncontrolled carry the highest burden of ongoing seizures – and the point at which they should be referred is often reached long before it is acted on.¹

Defining the threshold

The International League Against Epilepsy (ILAE) defines drug-resistant epilepsy as the failure of adequate trials of 2 tolerated, appropriately chosen and used ASM schedules – whether as monotherapy or in combination – to achieve sustained seizure freedom.^1,2

Each element of that definition carries weight. An "adequate" trial means a medication appropriate to the patient's seizure type or syndrome, used at an effective dose for a sufficient duration, and tolerated well enough to reach a therapeutically appropriate dose. Before applying the label, it is worth reassessing the original diagnosis, confirming the seizure type, reviewing medication adherence, verifying that the ASM was appropriate for the epilepsy type, and excluding pseudoresistance caused by subtherapeutic dosing, drug interactions, or nonepileptic events.¹

Applied consistently, the definition turns a vague sense that a patient is "difficult to control" into a defined clinical status that carries specific next steps.¹

Meeting the ILAE definition of drug-resistant epilepsy does not automatically mean a patient is a surgical candidate. Instead, it identifies patients who should have comprehensive re-evaluation to confirm the diagnosis, optimize medical management, and determine whether they may benefit from surgical, device-based, dietary, or other specialized therapies.¹

Why waiting rarely helps

The rationale for acting at the 2-drug threshold is that the odds of success decline with each subsequent agent. After 2 adequate, appropriately chosen, and tolerated ASM regimens have failed, the probability of achieving seizure freedom with further medication changes is substantially reduced. However, it is not eliminated, especially in focal epilepsy, noting that some patients can still benefit from additional therapies depending on epilepsy syndrome, etiology, and newer treatment options.¹

Repeated medication substitutions or escalating therapy without re-evaluating the diagnosis or treatment strategy tends to delay more definitive evaluation without improving the odds. That delay is not neutral: Mortality in epilepsy is elevated relative to the general population and concentrates among patients whose seizures remain uncontrolled, particularly those with ongoing generalized tonic clonic seizures, who are at increased risk for sudden unexpected death in epilepsy (SUDEP), so time spent on low-yield medication changes is also time spent at elevated risk. Earlier recognition of resistance is increasingly emphasized for exactly this reason.^1,3

Clusters and interim management

Uncontrolled epilepsy also changes the acute management picture. Seizure clusters are more common in patients with drug-resistant or refractory epilepsy, although they can still happen across the spectrum of epilepsy, which means this population is also the one most likely to need an out-of-hospital plan for acute repetitive seizures.⁴

While a referral is pending, an individualized acute plan – including a rescue benzodiazepine by an appropriate route, such as an intranasal or rectal formulation, along with clear instructions for patients and caregivers regarding when to administer rescue medication, when to activate emergency medical services, and when emergency department evaluation is warranted – gives patients and care partners a defined response to breakthrough clusters and is a reasonable part of interim management. Establishing that plan does not wait on the referral; it addresses the immediate risk while the longer evaluation proceeds.⁵

Making the referral

Meeting the 2-drug threshold is the signal to refer to a comprehensive epilepsy center. Beyond confirming or refining the diagnosis with video-electroencephalography (video-EEG), epilepsy protocol MRI, functional imaging, and multidisciplinary evaluation may identify a surgical epileptogenic focus or establish that events are nonepileptic. Such centers evaluate candidacy for potentially curative resective surgery, minimally invasive ablative procedures, neuromodulation (including vagus nerve stimulation, responsive neurostimulation, and deep brain stimulation), dietary therapies, genetic evaluation, and access to clinical trials.¹

Framing referral as a standard consequence of a defined status – rather than a last resort after years of trials – aligns community practice with where the evidence points and gives patients access to evaluation while the potential for seizure freedom is greatest.