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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice.
Brand Name
Zonisamide
Generic Name
Zonisamide
Active Ingredient
ZonisamideCategory
Anti-epileptic Agent [EPC]
Variants
47
Different strengths and dosage forms
| Strength | Form | Route | NDC |
|---|---|---|---|
| 100 mg/1 | CAPSULE | ORAL | 68788-4004 |
| 50 mg/1 | CAPSULE | ORAL | 70771-1143 |
| 100 mg/1 | CAPSULE | ORAL | 71205-727 |
References used for this content
This page is for informational purposes only and does not replace medical advice. Before using any prescription or over-the-counter medication for Zonisamide, you must consult a qualified healthcare professional.
| 25 mg/1 | CAPSULE | ORAL | 76282-226 |
| 50 mg/1 | CAPSULE | ORAL | 76282-227 |
| 25 mg/1 | CAPSULE | ORAL | 29300-428 |
| 100 mg/1 | CAPSULE | ORAL | 60687-230 |
| 100 mg/1 | CAPSULE | ORAL | 63187-583 |
| 100 mg/1 | CAPSULE | ORAL | 0615-8266 |
| 100 mg/1 | CAPSULE | ORAL | 62756-260 |
| 25 mg/1 | CAPSULE | ORAL | 68001-242 |
| 100 mg/1 | CAPSULE | ORAL | 70518-3180 |
+ 35 more variants
Detailed information about Zonisamide
Zonisamide is a benzisoxazole anticonvulsant (seizure medication) used as adjunctive therapy for partial-onset seizures in adults. It functions as a sodium and calcium channel blocker with weak carbonic anhydrase inhibitory activity.
For the treatment of partial-onset seizures in adults and adolescents over the age of 16, the dosing of Zonisamide follows a careful titration (gradual increase) schedule to minimize side effects.
Zonisamide is not FDA-approved for use in pediatric patients under the age of 16. However, it is sometimes used 'off-label' by pediatric neurologists.
Since Zonisamide is eliminated primarily by the kidneys, patients with kidney disease require extra caution. For patients with a glomerular filtration rate (GFR) less than 50 mL/min, the drug should be titrated more slowly, and the final maintenance dose may need to be lower. Zonisamide is contraindicated in patients with severe renal failure.
Because the liver (specifically the CYP3A4 enzyme) is responsible for metabolizing the drug, patients with liver impairment may experience slower clearance. Slower titration and frequent monitoring are required for these individuals.
Older adults often have reduced renal and hepatic function. Healthcare providers typically start elderly patients at the lowest possible dose and monitor closely for CNS side effects like confusion or dizziness, which can increase the risk of falls.
If you miss a dose, take it as soon as you remember. However, if it is almost time for your next scheduled dose, skip the missed dose and return to your regular schedule. Do not double the dose to catch up. Because Zonisamide stays in your system for a long time, a single missed dose is unlikely to trigger a seizure immediately, but consistency is key for long-term control.
Signs of a Zonisamide overdose may include extreme drowsiness, slowed heart rate (bradycardia), low blood pressure (hypotension), respiratory depression (shallow breathing), or loss of consciousness (coma).
Emergency Measures: If an overdose is suspected, call 911 or your local emergency services immediately. There is no specific antidote for Zonisamide. Treatment in a hospital setting typically involves gastric lavage (stomach pumping), intravenous fluids, and supportive care to maintain breathing and heart function. Due to its low protein binding, hemodialysis may be partially effective in removing the drug from the bloodstream.
> Important: Follow your healthcare provider's dosing instructions exactly. Do not adjust your dose or stop taking the medication without medical guidance, as sudden discontinuation can trigger status epilepticus (continuous seizures).
Most patients taking Zonisamide will experience some mild to moderate side effects, especially during the first few weeks of treatment or after a dose increase. These often include:
Zonisamide is a potent neurological medication that requires careful management. Patients must be aware that because it is a sulfonamide derivative, it carries risks similar to 'sulfa' antibiotics. If you have ever had a severe reaction to a sulfa drug, you must inform your doctor before starting Zonisamide.
No FDA black box warnings for Zonisamide as of 2024. However, the FDA requires a general warning for all anti-epileptic drugs regarding the increased risk of suicidal thoughts and behaviors.
While there are few absolute contraindications based solely on drug interactions, Zonisamide should not be used with other potent carbonic anhydrase inhibitors unless absolutely necessary.
There are specific circumstances where Zonisamide must never be used because the risks far outweigh any potential benefits:
Zonisamide is classified as Pregnancy Category C (by older FDA standards). Data from animal studies have shown that Zonisamide can cause structural abnormalities, including cardiovascular defects and skeletal variations, at doses similar to human therapeutic levels.
Zonisamide is excreted into human breast milk. The concentration in breast milk is similar to the concentration in the mother's plasma. Because of the potential for serious adverse reactions in nursing infants (such as somnolence or poor feeding), a decision should be made whether to discontinue nursing or discontinue the drug, taking into account the importance of the drug to the mother.
Zonisamide is a benzisoxazole anticonvulsant. Its primary molecular targets are voltage-gated sodium channels and T-type calcium channels. By binding to the sodium channels in their inactive state, Zonisamide prolongs the refractory period of the neuron, preventing the rapid, repetitive firing that leads to a seizure. Its action on T-type calcium channels in the thalamus helps to suppress the synchronized firing patterns often seen in generalized seizure activity. Additionally, Zonisamide provides a weak inhibition of carbonic anhydrase, which may alter the pH environment of neurons, further reducing excitability.
The pharmacodynamic effect of Zonisamide is characterized by a broad-spectrum stabilization of neuronal membranes. There is a clear dose-response relationship, with higher doses generally providing better seizure control but also a higher incidence of CNS side effects. Because of its long half-life, the clinical effects of a dose change may not be fully apparent for 14 days. Tolerance to the anti-seizure effects is rarely reported, making it a viable long-term treatment option.
Common questions about Zonisamide
Zonisamide is primarily used as an add-on treatment for partial-onset seizures in adults and adolescents aged 16 and older. It belongs to a class of medications called anticonvulsants, which help control the electrical activity in the brain to prevent seizures. Beyond its approved use, some doctors may prescribe it off-label for conditions like migraine prevention or weight management. It is considered a broad-spectrum agent, meaning it may be effective for several different types of seizures. Always consult your healthcare provider to see if this specific medication is appropriate for your diagnosis.
The most common side effects reported by patients taking Zonisamide include drowsiness (somnolence), dizziness, loss of appetite, and weight loss. Many people also experience a feeling of being 'slowed down' or having difficulty concentrating, often described as brain fog. Some patients may notice increased irritability or agitation during the first few weeks of treatment. Gastrointestinal issues like nausea or diarrhea are also relatively frequent. Most of these symptoms are dose-dependent and may improve as your body adjusts to the medication over time.
It is generally advised to avoid or strictly limit alcohol consumption while taking Zonisamide. Both Zonisamide and alcohol act as central nervous system depressants, meaning they slow down brain activity. Combining them can lead to extreme drowsiness, severe dizziness, and a significantly increased risk of falls or accidents. Furthermore, alcohol can lower the seizure threshold, potentially making your medication less effective at preventing seizures. If you choose to drink, it is vital to discuss the risks with your doctor first.
Zonisamide is generally not recommended during pregnancy unless the benefits of seizure control clearly outweigh the potential risks to the fetus. Animal studies have shown that the drug can cause birth defects, including heart and bone abnormalities. In humans, there is evidence that it may lead to infants being born smaller than average for their gestational age. If you are planning to become pregnant or find out you are pregnant while taking Zonisamide, contact your doctor immediately. They may suggest switching to a safer alternative or will monitor your pregnancy very closely.
Because Zonisamide has an exceptionally long half-life, it takes a significant amount of time to reach a steady level in your bloodstream. It usually takes about two weeks of consistent daily dosing to reach a 'steady state' where the drug's concentration remains stable. Consequently, you may not notice a full reduction in seizure frequency immediately after starting the medication or changing your dose. Your doctor will typically wait at least two weeks between dose increases to accurately assess how well the current dose is working. Patience is required during the titration phase of this treatment.
No, you should never stop taking Zonisamide suddenly unless specifically instructed by your doctor due to a severe allergic reaction. Abruptly discontinuing an anti-seizure medication can cause 'rebound' seizures, which may be more frequent or severe than those you had before. In some cases, it can lead to status epilepticus, a medical emergency where seizures do not stop. If you need to stop the medication, your doctor will provide a schedule to gradually taper your dose over several weeks. This allows your brain to adjust safely to the change.
If you miss a dose of Zonisamide, take it as soon as you remember. However, if it is almost time for your next scheduled dose, you should skip the missed dose and simply take the next one at your regular time. Do not take two doses at once to make up for the one you missed, as this can increase the risk of side effects. Because Zonisamide stays in your system for a long time, a single missed dose is unlikely to cause an immediate seizure, but you should strive for consistency. If you miss more than one dose, contact your healthcare provider for advice.
Unlike many other anti-seizure medications that are associated with weight gain, Zonisamide is actually more likely to cause weight loss. It often acts as an appetite suppressant, leading patients to feel less hungry and eat smaller portions. In clinical trials, a significant percentage of patients experienced noticeable weight loss while taking the drug. While this can be a beneficial side effect for some, it is important to monitor your weight and nutrition. If weight loss becomes excessive or leads to weakness, you should discuss it with your healthcare provider.
Zonisamide can interact with several other medications, so it is crucial to provide your doctor with a full list of everything you take. It is especially important to mention other seizure drugs like Phenytoin or Carbamazepine, as these can lower Zonisamide levels in your blood. You should also avoid taking it with Topiramate, as the combination increases the risk of kidney stones and metabolic acidosis. Because Zonisamide is processed by the liver's CYP3A4 enzyme, many common antibiotics and antifungals can also affect its levels. Always check with a pharmacist before starting any new prescription or over-the-counter drug.
Yes, Zonisamide is available as a generic medication and is generally much more affordable than the original brand-name version, Zonegran. Generic versions are required by the FDA to have the same active ingredient, strength, dosage form, and route of administration as the brand-name drug. Most insurance plans prefer the generic version. When switching from brand to generic, or between different generic manufacturers, some patients with very sensitive seizure disorders prefer to stay with one consistent supplier. Discuss with your pharmacist if you have concerns about the manufacturer of your generic Zonisamide.
Other drugs with the same active ingredient (Zonisamide)
> Warning: Stop taking Zonisamide and call your doctor immediately if you experience any of these serious symptoms.
With prolonged use, Zonisamide may affect bone mineral density due to chronic metabolic acidosis. This can increase the risk of osteomalacia or osteoporosis (weak bones). Regular monitoring of serum bicarbonate levels is recommended to mitigate this risk. Additionally, the long-term impact on cognitive function should be assessed periodically by a healthcare provider.
Currently, Zonisamide does not carry a specific FDA Black Box Warning. However, it does carry prominent 'Warnings and Precautions' regarding serious skin reactions, suicidality, and metabolic acidosis, which are considered nearly as critical as a black box designation.
Report any unusual symptoms or changes in your health to your healthcare provider immediately. Early intervention is key to managing side effects effectively.
Healthcare providers will typically order the following tests periodically:
Zonisamide may cause significant somnolence (drowsiness) and dizziness. Patients should not drive, operate heavy machinery, or engage in dangerous activities until they are certain the medication does not impair their ability to perform these tasks safely.
Alcohol should be avoided or strictly limited while taking Zonisamide. Alcohol can worsen the sedative effects of the medication, increasing the risk of respiratory depression, severe dizziness, and loss of coordination.
Never stop taking Zonisamide abruptly. Sudden discontinuation of any anti-seizure medication can lead to a rapid increase in seizure frequency or status epilepticus, a life-threatening condition of continuous seizures. If the drug must be stopped, it should be tapered (gradually reduced) over a period of at least two weeks under medical supervision.
> Important: Discuss all your medical conditions, especially kidney disease, liver disease, or a history of depression, with your healthcare provider before starting Zonisamide.
Zonisamide does not typically interfere with standard laboratory tests. However, it will cause a physiological decrease in serum bicarbonate and may cause a slight increase in serum creatinine and BUN levels due to its effect on the kidneys, which should be interpreted carefully by a physician.
For each major interaction, the mechanism usually involves the CYP3A4 enzyme pathway (metabolic interaction) or carbonic anhydrase inhibition (pharmacodynamic interaction). The clinical consequence is either reduced seizure control or increased drug toxicity. Management typically involves adjusting the dose of Zonisamide or selecting an alternative medication.
> Important: Tell your doctor about ALL medications, supplements, and herbal products you are taking, including over-the-counter pain relievers and cold medicines.
These are conditions where the drug should be used only if the benefit clearly outweighs the risk, and with extreme caution:
Patients should be aware of cross-sensitivity between Zonisamide and other sulfonamide-derived drugs. This includes certain antibiotics (like Bactrim), certain diuretics (like Furosemide or Hydrochlorothiazide), and certain diabetes medications (sulfonylureas). While not every patient with a 'sulfa' allergy will react to Zonisamide, the risk is high enough to warrant extreme caution or avoidance.
> Important: Your healthcare provider will evaluate your complete medical history, including all past allergic reactions, before prescribing Zonisamide.
As previously noted, Zonisamide is not approved for children under 16. The primary concern in children is oligohydrosis (lack of sweating) and hyperthermia. Children are more susceptible to heat-related illnesses while on this drug. Healthcare providers must educate parents to ensure children stay hydrated and avoid excessive heat exposure during play or sports.
Clinical studies of Zonisamide did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently than younger subjects. However, because elderly patients are more likely to have decreased renal function, dose selection should be cautious, usually starting at the low end of the dosing range. There is also a higher risk of CNS side effects like confusion and incoordination, which can lead to dangerous falls.
For patients with mild to moderate renal impairment, Zonisamide should be titrated more slowly. The drug's clearance is reduced by approximately 35% in patients with creatinine clearance between 20-50 mL/min. It is contraindicated in severe renal failure. Patients should have their serum bicarbonate and creatinine levels checked frequently.
In patients with mild to moderate hepatic impairment, the half-life of Zonisamide may be prolonged. While specific 'Child-Pugh' based dosing guidelines are not established in the official labeling, clinical practice dictates a slower titration (e.g., increasing the dose every 3-4 weeks instead of every 2 weeks) and close monitoring for signs of toxicity.
> Important: Special populations require individualized medical assessment. Never share your medication with others, especially those in these high-risk groups.
| Parameter | Value |
|---|---|
| Bioavailability | ~100% (Oral) |
| Protein Binding | 40% (primarily to albumin) |
| Half-life | 63 - 105 hours |
| Tmax | 2 - 6 hours |
| Metabolism | Hepatic (CYP3A4) |
| Excretion | Renal (62%), Fecal (3%) |
Zonisamide is classified as an Anti-epileptic Agent and specifically a Benzisoxazole derivative. It is often grouped with other 'second-generation' anticonvulsants. While it shares some functional similarities with Topiramate (such as carbonic anhydrase inhibition and weight loss effects), its chemical structure is distinct, providing an alternative for patients who may not tolerate other medications in the class.