Zonisamide (Zonegran)
Generic Name: Zonisamide
Brand Names: Zonegran, Zonisade
Drug Class: Anti-seizure medication (sulfonamide derivative; sodium/calcium channel blocker and carbonic anhydrase inhibitor)
Primary Uses: Focal (partial) seizures
Common Side Effects: Sleepiness, decreased appetite, dizziness, unsteadiness, irritability, difficulty with memory/concentration
What is Zonisamide?
Zonisamide is an anti-seizure medication used to help control seizures in people with epilepsy. It is typically used as an add-on (adjunctive) medication alongside other seizure medicines. It has the advantage of a long duration of action, which allows for once- or twice-daily dosing.
How It Works
Zonisamide works through several mechanisms in the brain. It blocks sodium channels and a type of calcium channel (T-type), which helps stabilize nerve cells and prevent the abnormal electrical activity that causes seizures. It is also a mild carbonic anhydrase inhibitor, which can affect the body’s acid-base balance.
Who Might Take This Medication?
Zonisamide is FDA-approved for:
- Adjunctive (add-on) therapy for focal (partial-onset) seizures in adults and patients 16 years and older
It is also sometimes used off-label for other seizure types, including generalized tonic-clonic seizures, absence seizures, and myoclonic seizures, under medical supervision.
Common Side Effects
Many people tolerate zonisamide well, especially after the first few weeks. Common side effects include:
- Sleepiness or fatigue (especially when starting)
- Decreased appetite and weight loss
- Dizziness
- Unsteadiness (ataxia)
- Irritability or agitation
- Difficulty with memory or concentration
Weight loss is common with zonisamide, particularly in people who are overweight before starting treatment. Maintaining a balanced diet and staying well-hydrated is important. Discuss any significant weight changes with your healthcare provider.
Less common but important side effects:
- Mood or behavioural changes, including depression, anxiety, or suicidal thoughts
- Kidney stones (increasing fluid intake may help reduce this risk)
- Decreased sweating (oligohidrosis), especially in children, which can lead to overheating
- Skin rash
- Nausea, abdominal pain, or constipation
- Speech difficulties or mental slowing
- Tingling or numbness (paresthesia)
If you experience a skin rash, decreased sweating with fever, sudden back or abdominal pain, blood in the urine, blurred vision, or concerning mood changes, contact your healthcare provider promptly.
Monitoring and Special Considerations
- Blood tests may be needed periodically, including serum bicarbonate (to check for metabolic acidosis), kidney function, and sometimes drug levels.
- Increasing fluid intake is recommended to help reduce the risk of kidney stones.
- Avoid using zonisamide with other carbonic anhydrase inhibitors (such as topiramate or acetazolamide) without close medical supervision, as this combination can worsen metabolic acidosis and increase kidney stone risk.
- Zonisamide is a sulfonamide derivative, so it is contraindicated in patients with a known sulfonamide allergy.
- Dose adjustments may be needed for people with kidney or liver problems.
- Avoid alcohol and other sedating medications, as they may increase drowsiness.
- Children should be monitored closely for decreased sweating and overheating, especially in warm weather.
Frequently Asked Questions
Q: How long does it take to work?
A: Zonisamide is usually started at a low dose and increased gradually over several weeks. Full seizure control may take several weeks as the dose is adjusted. Steady-state blood levels are typically reached within about 2 weeks at a stable dose.
Q: What if I miss a dose?
A: Take it as soon as you remember. If it is close to the next dose, skip the missed dose and continue your regular schedule. Do not double doses. If you miss several doses, call your doctor before restarting.
Q: Can zonisamide affect my mood or behaviour?
A: Yes. Some people may experience irritability, depression, anxiety, or difficulty concentrating. Report any concerning changes to your healthcare provider promptly.
Q: Can I drink alcohol while taking zonisamide?
A: Alcohol may increase drowsiness and other side effects. Moderation is recommended, and discuss any concerns with your doctor.
Q: Will this medication affect my weight?
A: Zonisamide commonly causes decreased appetite and weight loss. About one-third of patients may lose more than 5% of their body weight. Weight loss tends to be greater in people who are overweight before starting treatment and is usually reversible after stopping the medication.
Q: Can I take zonisamide during pregnancy or breastfeeding?
A: Animal studies suggest potential risks to the developing baby, and some human data raise concerns about babies being born small for gestational age. Zonisamide does pass into breast milk. Always discuss the risks and benefits with your doctor if you are pregnant, planning to become pregnant, or breastfeeding. Women of childbearing potential should use effective contraception during treatment and for one month after stopping.
Q: Do I need to drink more water while taking this medication?
A: Yes. Staying well-hydrated is recommended to help reduce the risk of kidney stones, which can occur with zonisamide use.
Q: How do I know if zonisamide is working?
A: Track your seizures and any side effects in a simple log. Discuss changes with your healthcare provider to adjust dosing if needed.
All of the possible uses, cautions, side effects, or interactions of this drug are not covered in this handout. If you want more information about this medication, ask your child’s doctor, pharmacist, or nurse. This information handout does not pertain to pregnancy or breastfeeding. Talk to your doctor if this is a concern.
This information is for educational purposes only and does not replace medical advice. Always consult your healthcare provider about medications and treatment decisions.