Zonisamide (may also be known by the brand name Zonegran) is an anticonvulsant that may be used in some cats with epilepsy. In this article, you will learn how zonisamide works, when it may be used, the side effects to look for in cats, and some common problems.
About zonisamide for cats
Zonisamide is an antiepileptic drug used by veterinarians in cats to treat a variety of cases where some form of epilepsy is present.
Seizures occur when sudden electrical discharges in the brain cause involuntary body movement, or seizures.
Patients who experience a seizure often lose consciousness, and then the body may experience muscle spasms, convulsions, or the pet may become completely paralyzed with stiff muscles. Drooling, urination, and bowel movements may also occur.
Seizures can occur for a variety of reasons. The presence of brain tumors and inflammatory lesions in the brain may be a group of reasons for the presence of structural abnormalities. Pets may also experience seizures due to certain underlying medical conditions, such as liver and kidney disease, toxin ingestion, or hypoglycemia in cats with diabetes.
But seizures can also occur secondary to a condition called idiopathic epilepsy. With epilepsy, overexcitation of the nervous system can cause seizures, but there is no known cause. Pets with epilepsy usually have a normal MRI (magnetic resonance imaging) scan of the brain.
As an anticonvulsant drug, zonisamide helps reduce the chance of seizures and reduces the frequency of seizures by reducing the abnormal electrical activity that causes seizures. There are several types of antiepileptic drugs available, each of which works differently, and some are more effective than others in some situations.
What does zonisamide do in cats?
The mechanism of action of zonisamide is unknown. However, it is thought to work on sodium and calcium channels, which help stabilize nerve cells and dampen the domino effect of electrical activity that leads to seizures.
Zonisamide also affects certain neurotransmitters in the brain that support serotonin and dopamine (mood and pleasure hormones), but not GABA (sedation hormone). Zonisamide is also said to help scavenge damaging free radicals in the brain.
Zonisamide has been studied in dogs more than in cats, and it is not generally considered the anticonvulsant of choice for kittens. More common first-line options may include phenobarbital or levetiracetam (Keppra).
More commonly, zonisamide may be turned to when first-line anticonvulsants do not adequately control seizures, or if the cat experiences unacceptable side effects with another anticonvulsant, which leads to exploration of other drug options.
While there hasn’t been a ton of research on the use of zonisamide as a single anticonvulsant or monotherapy in cats, there are certainly anecdotal reports from individual cases where cats have behaved well to it.
Zonisamide also tends to be a relatively inexpensive drug when administered to cats, which may also highlight that it can be an advantageous option in certain circumstances.
Zonisamide is usually given to cats only once a day and may be a more favorable option than phenobarbital, which needs to be given every 12 hours, or Keppra, which usually needs to be given every 8 hours.
Zonisamide side effects in cats
Zonisamide has a higher risk of side effects in cats.
In one study, approximately 50% of cats treated with zonisamide experienced adverse reactions, most commonly including loss of appetite, diarrhea, vomiting, balance problems while walking (ataxia), and sedation/somnolence (somnolence) .
In another review of case reports, most cats appeared to have no side effects from zonisamide. However, the drug’s efficacy or benefit and safety as a single treatment were considered weak.
Zonisamide is considered a teratogen, which means it can cause birth defects if used in a pregnant woman. This has not been specifically documented in cats, but has been found in mice, rats, dogs and humans.
For this reason, it is recommended that any oral zonisamide medication be administered to your cat using disposable gloves.
Since zonisamide is primarily metabolized by the liver and excreted by the kidneys, it should be used with caution in pets with any pre-existing liver or kidney disease.
If you are concerned that your kitten may experience side effects from zonisamide, or if you suspect an overdose, please contact your veterinarian, the ASPCA Animal Poison Control Center (1-888-426-4435), or the Pet Poison Helpline (1 -855-764-7661) for further advice immediately.
Zonisamide cat dosage
The dosage of zonisamide for cats varies widely. Your veterinarian may adjust the dose based on whether it is used alone or in combination with another drug. It is also possible to start with a lower dose to see how the kitten tolerates it before increasing the dose further.
Because of these variations and precautions, it is best to have the appropriate oral dose of zonisamide for cats determined by the attending veterinarian, and for these reasons no specific dose is provided.
Of note, unlike canine zonisamide, which is usually given every 12 hours, feline zonisamide is usually given only once a day.
Although zonisamide can certainly have adverse effects, it is important not to stop the drug suddenly, especially if your cat has been taking it for a long time. Always talk to your veterinarian first.
Stopping any antiseizure medication suddenly may cause rebound seizures.
Zonisamide is unlikely to have any drug interactions with other commonly prescribed medications. Most notably, however, if the kitten is also taking phenobarbital for seizures, the dosage may need to be adjusted.
Zonisamide is a drug commonly used to help with epilepsy in pets. In cats, it may be considered more as a backup or add-on therapy for seizures than as a primary first-line option.
Cats may be at higher risk for adverse reactions, so a cat’s tolerance to a drug may be an important factor in deciding whether to use it as a treatment option.
frequently asked questions
Is zonisamide safe for cats?
All medicines carry a risk of side effects, but zonisamide may be more frequent in kittens. According to one study, approximately 50% of cats experience adverse reactions such as loss of appetite, vomiting, diarrhea, and lethargy. Zonisamide also may not be an advisable choice in cats with pre-existing liver or kidney disease.
In cats with no pre-existing liver or kidney disease who appear to tolerate drug therapy well, it may otherwise be considered a safe drug to continue, especially if it helps control epilepsy.
How long does it take for zonisamide to work in cats?
In cats, the onset of action of zonisamide is about 4 hours. Like many anticonvulsant drugs, it may take time for the dose to reach a “steady state,” a state in which drug levels are consistently high enough to prevent seizures.
Seek immediate veterinary care anytime a patient convulses violently for more than three minutes. Also, never attempt oral anticonvulsant medication while the pet is actively grasping, as this greatly increases the risk of being bitten by the person attempting to administer the medication, is less likely to be swallowed correctly by the patient, and may present a choking hazard.
What are the side effects of zonisamide?
Zonisamide may have several side effects, including decreased appetite, vomiting, diarrhea, problems with balance when walking (called ataxia), and drowsiness (excessive sleepiness).
In some studies, these effects were seen in approximately 50% of cats, while in others, the percentage was found to be lower.
What types of seizures does zonisamide treat?
Zonisamide is most commonly used in pets as an add-on therapy for epilepsy. Seizures are caused by overexcited electrical activity in the brain. In idiopathic epilepsy, there is no known cause, but it can sometimes be related to external triggers such as stress or loud noises.
Seizures can also be caused by lesions within the brain, such as tumors or inflammatory masses. Previous trauma that caused damage to brain tissue may also lead to seizures.
Like all anticonvulsants, zonisamide can be used in any situation where a seizure occurs, as a way to reduce the likelihood of a seizure by calming electrical excess activity in the brain through different mechanisms.
However, different anticonvulsants have different mechanisms of action and different degrees of efficacy. While zonisamide can be used to treat any type of epilepsy, it is most commonly used in cats as an adjunct or secondary option to help control seizures.
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