Drug-resistant epilepsy in dogs: what to check first
3-year-old Australian Shepherd with idiopathic epilepsy (Tier II) on phenobarbital for 6 months. It has 3–4 seizures a month. The owner admits sometimes forgetting the evening dose. Serum phenobarbital: 14 mg/L (range 15–35).
What is most appropriate?
chevron_right Show answer and explanation
A. It is drug-resistant: add potassium bromide
A dog with subtherapeutic levels and poor compliance cannot be considered drug-resistant. Adding a second drug now would be premature.
B. It is drug-resistant: add zonisamide
Same mistake: optimise the first drug before combining. Phenobarbital also lowers zonisamide levels.
C. Switch to imepitoin because phenobarbital has failed
Phenobarbital has not failed: it has not been given at a sufficient dose or regularly enough. Imepitoin is also not the best option in a dog with frequent seizures.
D. It does not meet drug-resistance criteria: improve compliance and raise the dose into the therapeutic range
Correct. Drug resistance requires failure of two well-chosen antiepileptics at adequate, well-tolerated doses. Review diagnosis, compliance and levels before changing strategy.
lightbulb Key takeaway
When control is poor, review: is the diagnosis right (rule out structural disease or non-epileptic events)? Is the medication given correctly? Are levels in range? Australian Shepherds, Border Collies and German Shepherds are at higher risk of severe, drug-resistant epilepsy.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.