Epilepsy is a commonly encountered condition in small animal practice. Despite the demonstrated efficacy of traditional anticonvulsant drugs such as phenobarbital and bromide, a significant proportion of canine and feline epileptics experience inadequate seizure control or intolerable adverse effects associated with these drugs.1-4
Alternative anticonvulsant drugs (AACDs) such as felbamate,5 gabapentin,4 levetiracetam,3,6 pregabalin,7 topiramate, and zonisamide1 have shown promise for the management of veterinary seizure disorders, and their use is becoming more widespread in veterinary neurology.
With an understanding of the pharmacology and practical considerations of AACDs, clinicians can effectively incorporate these drugs into routine practice, leading to improved seizure control and better quality of life for epileptic pets and their owners.
Traditional anticonvulsant drug doses can often be decreased or even discontinued in pharmacoresistant epileptic patients that have a good to excellent response to AACDs.
Pharmacoresistant epilepsy is inadequate seizure control despite documentation of therapeutic steady-state serum concentrations of one or more traditional anticonvulsants, such as phenobarbital or bromide.6 This is the most common indication for adjunctive use of AACDs.1-7
Idiopathic or Secondary Epilepsy
Any of the AACDs described here could be used as a primary monotherapy for dogs or cats with idiopathic or secondary epilepsy. AACDs should be considered as a primary therapeutic option for:
- Owners who have concerns about the common adverse effects associated with phenobarbital or bromide treatment for canine or feline epileptics
- Dogs and cats with secondary epilepsy resulting from malformation (eg, hydrocephalus), meningoenceph-alitis, or a brain tumor that may have a compromised level of consciousness or other neurologic dysfunction as a result of their disease (AACDs will not result in further sedation, a common effect of phenobarbital and bromide)
- Epileptic dogs or cats that have coincidental disease or are receiving concurrent drugs with known or potential interactions with phenobarbital or bromide
Pharmacointolerant epilepsy is considered to be present in animals that are on phenobarbital and/or bromide and experience clinically intolerable adverse effects, such as sedation, ataxia, polyphagia, polyuria, or polydipsia, at serum concentrations necessary to achieve adequate seizure control.
Although any AACD could be used in cases of pharmacointolerant epilepsy, levetiracetam is a popular choice in this clinical situation because it is rarely associated with adverse effects and rapidly confers anticonvulsant activity.3,6 This allows an immediate decrease in the dose of the problematic traditional anticonvulsant while minimizing the risk for breakthrough seizures.
Felbamate is contraindicated in myelosuppressed patients.5 The proprietary liquid formulation of gabapentin (Neurontin, pfizer.com) is also contraindicated for dogs because it contains xylitol. Zonisamide should be avoided in animals with a history of or predisposition to sulfonamide sensitivity.1 All AACDs should be used with caution and at appropriately modified doses in animals with significant hepatic or renal dysfunction.