Only a few antiepileptic drugs are efficacious for seizure disorders in dogs. Treatment outcome is not always satisfactory, with resistance to medication seen in about one third of cases. Commonly used drugs can also cause transient side effects such as sedation and ataxia. However, most of the newer antiepileptic drugs are not recommended in dogs because of their short half-lives. One exception is the drug zonisamide, which has a half-life of about 15 hours in dogs. Limited data exist on the use of this drug to treat canine epilepsy, but in a study by the author, it was seen to have a beneficial effect when used in conjunction with other antiepileptic drugs in some dogs with refractory epilepsy. In cases where good seizure control was obtained, it was also possible to decrease the dose of the first anticonvulsant medication. Another drug that may prove useful as add-on therapy for dogs with refractory seizures is levetiracetam. This drug acts by binding to a different receptor than other anticonvulsants and was recently developed in human medicine. Variable results for the drug were seen by the author when tested on dogs with refractory seizures. A third drug, ELB138, was also evaluated. The mechanism of action is not fully understood, but a pilot study has shown potent anticonvulsant effects in dogs with idiopathic epilepsy. ELB138 is equipotent to conventional anticonvulsants (eg, phenobarbital and primidone) and chronic administration was well tolerated, with fewer side effects than seen with traditional anticonvulsants. Further studies will be necessary to support these findings.
COMMENTARY: Patients with seizure disorders are commonly evaluated and managed by veterinary clinicians. There have been several anticonvulsants routinely used for the management of seizure disorders, particularly in dogs. These agents have included phenobarbital, benzodiazepines, and potassium bromide. In recent years there have been additional agents developed for the treatment of seizure disorders in people. In many cases they have not been efficacious in dogs due to pharmokinetics and limited half lives. Three anticonvulsants are mentioned in this series of reports that show promise for managing epilepsy in the dog. These studies emphasize these additional agents may be used to manage idiopathic epilepsy in cases where the side effects of previous anticonvulsant therapy are not tolerated or therapeutic goals are not met. Although these studies reported on a small number of patients, they indicate that these agents may show promise and further investigation is required.
How to treat a dog with seizures: Update on new medications. Tipold A. NAVC PROC 2009, pp 827-829.