- A definition of refractory epilepsy is not established for dogs, but it is generally agreed that an animal with frequent or severe seizures or intolerable side effects despite appropriate antiepileptic drug (AED) therapy is considered refractory to treatment.3
- Levetiracetam and zonisamide are increasingly the drugs of choice for monotherapy by some neurologists. A recent study found no reduction in monthly seizure frequency when levetiracetam was used as a sole agent.4 However, little additional information is available in the veterinary literature on the efficacy of these medications as sole agents.
- Some AEDs (eg, levetiracetam, zonisamide) have a reported “honeymoon effect,” with dogs developing tolerance over time.
- Gabapentin and pregabalin are not known efficacious AEDs but anecdotally may help with seizure control in patients tolerant to other medications.
*Idiopathic epilepsy can be subclassified into genetic epilepsy (identified genetic background), suspected genetic epilepsy (breed prevalence >2%), or epilepsy of unknown cause (nature unknown with no structural disease).5 Diagnosis of idiopathic epilepsy can be suggested if there is a history of ≥2 unprovoked epileptic seizures occurring ≥24 hours apart, the patient’s age at epileptic seizure onset is between 6 months and 6 years, interictal physical and neurologic examinations are unremarkable (except for antiepileptic-drug–induced neurologic abnormalities and postictal neurologic deficits), and no clinically significant abnormalities are found on minimum database blood tests and urinalysis.6 However, diagnosis is ideally made on exclusion (ie, normal brain MRI and CSF analysis) or further supported by electroencephalography.5
AED = antiepileptic drug
1. Podell M, Volk HA, Berendt M, et al. 2015 ACVIM small animal consensus statement on seizure management in dogs. J Vet Intern Med. 2016;30(2):477-490.
2. Muñana KR, Nettifee-Osborne JA, Papich MG. Effect of chronic administration of phenobarbital, or bromide, on pharmacokinetics of levetiracetam in dogs with epilepsy. J Vet Intern Med. 2015;29(2):614-619.
3. Muñana KR. Management of refractory epilepsy. Top Companion Anim Med. 2013;28(2):67-71.
4. FredsØ N, Sabers A, Toft N, MØller A, Berendt M. A single-blinded phenobarbital-controlled trial of levetiracetam as mono-therapy in dogs with newly diagnosed epilepsy. Vet J. 2016;208:44-49.
5. Berendt M, Farquhar RG, Mandigers PJJ, et al. International veterinary epilepsy task force consensus report on epilepsy definition, classification and terminology in companion animals. BMC Vet Res. 2015;11:182.
6. De Risio L, Bhatti S, Muñana K, et al. International veterinary epilepsy task force consensus proposal: diagnostic approach to epilepsy in dogs. BMC Vet Res. 2015;11:148.
- Farnbach GC. Serum concentrations and efficacy of phenytoin, phenobarbital, and primidone in canine epilepsy. J Am Vet Med Assoc. 1984;184(9):1117-1120.
- Holliday TA. Seizure disorders. Vet Clin North Am Small Anim Pract. 1980;10(1):3-29.
- Knowles K. Idiopathic epilepsy. Clin Tech Small Anim Pract. 1998;13(3):144-151.
- Kwan P, Schachter SC, Brodie MJ. Drug-resistant epilepsy. N Engl J Med. 2011;365(10):919-926.
- Lane SB, Bunch SE. Medical management of recurrent seizures in dogs and cats. J Vet Intern Med. 1990;4(1):26-39.
- Podell M, Fenner WR. Bromide therapy in refractory canine idiopathic epilepsy. J Vet Intern Med. 1993;7(5):318-327.
- Schwartz-Porsche D, Löscher W, Frey HH. Therapeutic efficacy of phenobarbital and primidone in canine epilepsy: a comparison. J Vet Pharmacol Ther. 1985: 8(2):113-119.
- Thomas WB. Idiopathic epilepsy in dogs and cats. Vet Clin North Am Small Anim Pract. 2010;40(1):161-179.
- von Klopmann, Rambeck B, Tipold A. Prospective study of zonisamide therapy for refractory idiopathic epilepsy in dogs. J Small Anim Pract. 2007;48(3):134-138.
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