A seizure is a sudden burst of abnormal electrical activity in the brain. Epilepsy is a brain condition that causes repeated seizures, and veterinarians commonly diagnose it after two or more unprovoked seizures that happen more than 24 hours apart. When no brain injury or other illness is found to explain the seizures, it is called idiopathic epilepsy, and the cause is often genetic (Merck Veterinary Manual).
Veterinarians treat epilepsy with a daily maintenance medication and adjust it over time, using how well seizures are controlled and, for some medications, blood levels (Merck Veterinary Manual). Bayview Pharmacy compounds the seizure medications veterinarians order most often for pets, prepared to the strength and form your veterinarian specifies. They are part of our veterinary compounding line, alongside methimazole for cats, pimobendan for dogs, and trilostane for dogs.
What does a seizure look like?
In a generalized seizure, the pet suddenly loses consciousness, the legs move uncontrollably, and there may be drooling, dilated pupils, vocalizing, or loss of bladder or bowel control. Focal seizures start in one area of the brain and affect one part of the body, such as twitching of the face. Some pets show behavior changes hours or even days before a seizure, and afterward a pet may be disoriented, restless, or pace while it recovers (Merck Veterinary Manual). In cats, seizures can also look like sudden jumping, growling, chewing at the tail, drooling, or facial twitching (Veterinary Sciences).
When is a seizure an emergency?
Call your veterinarian or go to an emergency animal hospital right away if a seizure lasts longer than 5 minutes, if your pet has two or more seizures within 24 hours, or if your pet does not recover normally between seizures. Seizures that go on too long can cause dangerous overheating, low blood sugar, and swelling of the brain. A first-ever seizure also needs a prompt veterinary visit (Veterinary Sciences). Emergency seizure care is your veterinarian's to give; the medications on this page are for daily, long-term use.
How does it work?
Levetiracetam binds to a protein in nerve endings called SV2A and reduces the release of glutamate, a chemical that excites the brain (Merck Veterinary Manual).
Zonisamide is a sulfonamide-type anticonvulsant. Its exact action is not known, but it may calm overactive nerve signaling through sodium and calcium channels (Merck Veterinary Manual).
Potassium bromide steadies nerve cell membranes by interfering with the movement of chloride and strengthening the effect of GABA, the brain's main calming signal (Merck Veterinary Manual).
Gabapentin reduces the calcium flow nerves need to release excitatory chemicals, and in dogs it has been studied as an add-on to other seizure medications (Merck Veterinary Manual). In people, levetiracetam, zonisamide, and gabapentin are anticonvulsants described as decreasing abnormal excitement or electrical activity in the brain (MedlinePlus: levetiracetam, zonisamide, gabapentin).
Phenobarbital is not compounded on this page, but it is a common first choice: phenobarbital and bromide are considered first-line maintenance medications in dogs, and phenobarbital is a first-line choice in cats (Merck Veterinary Manual).
What is it used for?
Veterinarians prescribe these medications as daily, long-term treatment for epilepsy and recurring seizures. Maintenance medication is typically started after more than two seizures within six months, after a cluster of seizures, or after a prolonged seizure (Merck Veterinary Manual). The goals are to reduce or eliminate seizures, make them less severe, and avoid side effects (ACVIM consensus statement). Your veterinarian may start with one medication and add or change medications if seizures continue. A calendar of your pet's seizures helps your veterinarian judge how treatment is going (Merck Veterinary Manual), and for some medications, such as potassium bromide and zonisamide, blood levels are checked to guide the dose (ACVIM consensus statement).
Liquid or capsule?
Levetiracetam and zonisamide are compounded as oral liquids measured with a syringe, which lets small doses be matched to a pet's weight. Potassium bromide is prepared as a 250 mg/mL liquid or as 500 mg and 750 mg capsules, for dogs only. Gabapentin is compounded as a liquid when your veterinarian adds it to a seizure plan. The human gabapentin oral solution sold in pharmacies contains xylitol, which can cause liver failure in dogs (Merck Veterinary Manual) and can quickly drop a dog's blood sugar (FDA), so do not substitute a human liquid without asking your veterinarian. If your pet takes one form more reliably than another, tell your veterinarian. Other medications we prepare as liquids are on our custom oral suspensions page.
How is it given?
All of the medications on this page are given by mouth. Your veterinarian sets the dose, which is specific to your pet, and how often to give it. Shake liquids well and measure each dose with the oral syringe provided, never a kitchen spoon. Give doses at the same times each day, refill before the bottle runs out, and never stop or skip a seizure medication on your own: when a medication needs to be stopped, veterinarians lower the dose gradually over a few weeks to avoid bringing on a seizure (Merck Veterinary Manual). If your dog takes potassium bromide, keep the food and treats the same, because a change in diet, especially in salt (chloride), changes bromide levels (Merck Veterinary Manual; FDA).
Side effects & safety
The most common effects of seizure medications are sleepiness and unsteady walking, especially when a medication is started or the dose goes up (Merck Veterinary Manual). Potassium bromide commonly causes increased thirst, urination, and appetite (Merck Veterinary Manual), and pancreatitis has been reported (ACVIM consensus statement). Signs that a bromide level is too high include depression, behavior changes, poor coordination, and weakness in the back legs (FDA). Levetiracetam can cause vomiting, sleepiness, unsteadiness, or restlessness in dogs, and drooling has been reported in cats (Merck Veterinary Manual). Zonisamide's effects are usually mild, such as unsteadiness, poor appetite, tiredness, and vomiting (Merck Veterinary Manual), but rare liver problems, a kidney-related acid problem, and dry eye have been reported, so your veterinarian may check bloodwork (ACVIM consensus statement). Contact your veterinarian about any change that worries you.
Which pets should not take it?
Potassium bromide should not be given to cats. In cats it can cause a serious, sometimes fatal, lung condition with coughing (Merck Veterinary Manual), and the approved potassium bromide product is labeled not for use in cats (FDA product label). Zonisamide is a sulfonamide-type drug and should not be prescribed for pets that have reacted to sulfa drugs (Merck Veterinary Manual). Levetiracetam leaves the body through the kidneys, so it is used with caution in pets with kidney disease (Merck Veterinary Manual), and dogs with reduced kidney function are more prone to bromide toxicity (FDA product label). Safe use of potassium bromide has not been evaluated in dogs that are pregnant, nursing, or intended for breeding (FDA product label). Tell your veterinarian about your pet's full history and every other medication and supplement.
How should it be stored?
Store each medication as directed on its label, keep the container tightly closed, and keep it out of reach of children and other pets. The FDA label for potassium bromide chewable tablets warns that it is not for human use and to contact a physician if a person swallows it (FDA product label). Do not use a preparation after its beyond-use date, and ask your pharmacist how to dispose of any unused medication.
Why is this compounded?
The approved potassium bromide and phenobarbital tablets are labeled for dogs only and come in fixed tablet sizes, and there is no FDA-approved veterinary levetiracetam or zonisamide. Compounding is for strengths, flavors, and forms those products do not cover, such as a liquid measured by syringe for a small dog or a cat, or a potassium bromide capsule in a strength the tablets do not come in. It is prescribed when your veterinarian decides an approved product is not suitable for that animal. A compounded preparation is made for one pet on one prescription; it is not a generic version of an approved product. The rest of what we compound for animals is in our compounded medications catalog.
Clinical details for prescribers
Regulatory status. Levetiracetam, zonisamide, potassium bromide, and gabapentin are not federally controlled substances; phenobarbital is Schedule IV (DEA). Approved animal products for canine idiopathic epilepsy: KBroVet, potassium bromide chewable tablets, fully approved after conditional approval as KBroVet-CA1 (FDA), and Fidoquel-CA1, phenobarbital tablets, conditionally approved (FDA; 21 CFR 516.1760). Both labels state not for use in cats (FDA product label; Fidoquel-CA1 label). Imepitoin is FDA-approved in the US for noise aversion in dogs, not for epilepsy (21 CFR 520.1150). Levetiracetam is not labeled for use in dogs and cats (Merck Veterinary Manual), and Part 520 has no approved oral animal drug entry for levetiracetam, zonisamide, or gabapentin (21 CFR Part 520). Each preparation is compounded for an individual animal on a valid prescription within a veterinarian-client-patient relationship, as extralabel use under AMDUCA (FDA); animal drugs compounded from bulk drug substances follow FDA's GFI #256.
Formulation and dosing. Levetiracetam 100 mg/mL oral suspension; zonisamide 20 and 50 mg/mL oral suspension; potassium bromide 250 mg/mL oral solution and 500 and 750 mg capsules (dogs only); gabapentin 100 and 300 mg/mL oral suspension as an add-on. Reported dosing: levetiracetam immediate-release 20 to 60 mg/kg PO every 8 hours, or extended-release tablets 30 mg/kg PO every 12 hours (Merck Veterinary Manual); zonisamide 5 to 10 mg/kg PO every 12 hours in dogs and cats (Merck Veterinary Manual), with 5 to 15 mg/kg every 12 hours and a 10 to 40 mcg/mL target range described in dogs (ACVIM consensus statement); potassium bromide starting at 40 mg/kg/day in dogs (ACVIM consensus statement), with a labeled total daily range of 25 to 68 mg/kg for the approved chewable (FDA product label).
Counseling and clinical points:
- Bromide elimination half-life in dogs is 25 to 46 days, so steady state can take up to 4 months; a loading dose is used when faster control is needed (Merck Veterinary Manual). Pelvic limb ataxia, weakness, and altered behavior are more likely above 3000 mg/L (ACVIM consensus statement).
- High-chloride diets increase renal bromide excretion and lower serum concentrations (Merck Veterinary Manual). Monitor with diet changes, chloride-containing IV fluids, and concurrent medications; decreased renal function predisposes to bromide toxicosis (FDA product label).
- Bromide is no longer recommended as a maintenance anticonvulsant in cats because of bronchial disease with cough and pulmonary infiltrates (Merck Veterinary Manual); coughing was reported in 35 to 42 percent of treated cats in one review (Kline).
- Levetiracetam is excreted largely unchanged in urine; use caution in renal disease. Routine serum monitoring is generally not required. The extended-release tablet must stay whole, so confirm the dosage form at each refill (Merck Veterinary Manual).
- Zonisamide is contraindicated with sulfonamide hypersensitivity (Merck Veterinary Manual). Idiosyncratic hepatopathy, renal tubular acidosis, keratoconjunctivitis sicca, and polyarthropathy have been reported; assess hepatic enzymes, electrolytes, blood gas, and hematology before starting (ACVIM consensus statement). Counsel cat owners on the limited clinical evidence in cats (Merck Veterinary Manual).
- The commercial human gabapentin oral solution contains xylitol (300 mg/mL) and should not be used in dogs (Merck Veterinary Manual; FDA).
- Taper any anticonvulsant over a few weeks when discontinuing; abrupt withdrawal can precipitate seizures (Merck Veterinary Manual).
Status epilepticus and cluster seizures are managed by the treating veterinarian or an emergency service (Veterinary Sciences). Account setup and ordering are covered on our for providers page.
References
- Merck Veterinary Manual: Epilepsy in small animals
- Merck Veterinary Manual: Anticonvulsants for animals
- ACVIM consensus statement: Seizure management in dogs
- Veterinary Sciences: Emergency approach to acute seizures
- Feline seizure disorders and treatment options
- FDA: KBroVet approval
- FDA label: KBroVet-CA1
- FDA: Fidoquel-CA1 conditional approval
- FDA label: Fidoquel-CA1
- 21 CFR 516.1760: Phenobarbital
- 21 CFR 520.1150: Imepitoin
- 21 CFR Part 520: Oral dosage form new animal drugs
- FDA: Xylitol is dangerous for dogs
- FDA: Extra-label drug use in animals
- FDA: GFI #256
- DEA: Controlled substances list
- MedlinePlus: Levetiracetam
- MedlinePlus: Zonisamide
- MedlinePlus: Gabapentin
Seizure Medications for Dogs & Cats are compounded veterinary medications and are not FDA-approved. This information is educational and is not a substitute for your veterinarian's instructions. Your veterinarian determines whether a medication is appropriate and sets the dose.
