What is drug-resistant epilepsy?

In veterinary medicine, drug-resistant epilepsy — sometimes called refractory epilepsy — generally refers to inadequate seizure control despite appropriate trials of at least two anti-seizure medications at adequate doses and appropriate monitoring. This definition is adapted from human epilepsy medicine and applied clinically in veterinary neurology; there is no single universally standardized veterinary definition. Adequate seizure control is generally defined as a reduction in seizure frequency of 50% or more, with no seizure-free periods shorter than three times the pre-treatment inter-seizure interval.

In dogs, published estimates suggest that approximately 20–30% may be classified as drug-resistant despite appropriate first- and second-line treatment. This is a significant proportion — and if your pet falls into this category, you are not alone, and there are options to explore.

Before accepting drug resistance — what to rule out first

Before concluding that a pet is truly drug-resistant, several factors should be reviewed:

• Medication compliance — Is medication being given consistently, at the correct dose, at the correct times? Missed doses or inconsistent timing are a common cause of apparent treatment failure
• Blood levels — Is the medication reaching adequate blood levels in this individual pet? Some pets metabolize drugs unusually quickly or slowly
• Diagnosis accuracy — Has the underlying cause been appropriately investigated? Some cases of apparent idiopathic epilepsy may have a structural cause that hasn't been identified
• Drug interactions — Are other medications or supplements interfering with anti-seizure drug effectiveness?

Add-on medications

When a first-line drug (typically phenobarbital) provides insufficient seizure control, the standard approach is to add a second agent rather than replace the first:

• Potassium bromide — The most established add-on therapy in dogs; takes months to reach stable levels
• Levetiracetam (Keppra) — Increasingly used as an add-on; available in extended-release formulation
• Zonisamide — Another newer anti-seizure agent used in veterinary neurology; fewer interactions than some older drugs
• Pregabalin — Emerging use in veterinary epilepsy; requires further study
• Imepitoin — Available in Europe; used as first- or second-line agent

Specialist referral

Drug-resistant epilepsy is one of the clearest indications for referral to a veterinary neurologist. Specialists have access to a broader range of medication options, can perform more advanced monitoring, and may be able to offer clinical trial participation. If your pet's seizures are not adequately controlled on first-line treatment, ask your veterinarian for a neurology referral.

Dietary adjuncts

MCT-enriched diets have demonstrated seizure reduction in clinical trials (see Guide 12) and are considered a reasonable adjunctive approach in drug-resistant cases. The evidence is modest but the approach is low-risk and may provide additional benefit alongside medication.

Managing expectations

Complete seizure freedom is not achievable for all pets with epilepsy, particularly those with drug-resistant disease. The goal shifts from elimination to meaningful reduction — fewer seizures, less severe seizures, and the best possible quality of life for both the pet and the owner. Research supports that many pets with drug-resistant epilepsy can still have acceptable quality of life with optimized multi-drug treatment and proactive management.