Zonisamide

About Zonisamide

How zonisamide prevents seizures is not fully known; it may act on sodium and calcium channels in nerve cells, and it also inhibits the enzyme carbonic anhydrase. The capsules are approved as add-on treatment for partial seizures in adults with epilepsy, and their label says safety and effectiveness under 16 have not been established; Zonisade is approved as add-on treatment for partial-onset seizures in adults and children 16 and older. Both start at 100 mg a day and rise by 100 mg no faster than every two weeks, taken once or twice daily with or without food; the capsule label notes no sign of a greater response above 400 mg a day. Levels can take up to two weeks to settle after each change.

There is no boxed warning, but because zonisamide is a sulfonamide, rare and sometimes fatal reactions have occurred, including Stevens-Johnson syndrome, toxic epidermal necrolysis, sudden severe liver damage, agranulocytosis and aplastic anemia; a rash, fever, sore throat, mouth sores or easy bruising means calling the doctor at once. Children taking it have had reduced sweating and overheating, sometimes heat stroke needing hospital care. It can cause metabolic acidosis (too much acid in the blood), so bicarbonate is measured before and during treatment, and kidney stones, which drinking more fluid may help prevent. Other warnings cover DRESS (a multi-organ allergic reaction), sudden nearsightedness with angle-closure glaucoma, suicidal thoughts, high ammonia levels, and nervous system effects such as depression, slowed thinking and trouble finding words. Sleepiness, loss of appetite, dizziness, unsteadiness, irritability and trouble with memory or concentration are the most common side effects.

Stopping suddenly can bring on seizures, so it is tapered. Zonisamide harmed the fetus in several animal species, so the label advises effective contraception (for Zonisade, during treatment and for one month after); it passes into breast milk, and the Zonisade label advises watching a nursing infant for poor feeding, weight loss, excess sleepiness, decreased muscle tone and a raised temperature. Both labels say not to use it in kidney failure (an estimated GFR below 50 mL/min). Zonisade is a strawberry-flavored liquid, 100 mg per 5 mL, thrown away 30 days after opening. Zonegran is still sold in 25 and 100 mg, but its 50 mg capsule has been discontinued.

Taking Zonisamide

How to take it

Once or twice a day as prescribed, with or without food. Swallow capsules whole, without splitting, chewing or crushing them; shake Zonisade well before every dose and measure it with an accurate measuring device, not a household teaspoon. MedlinePlus advises six to eight glasses of water a day.

If you miss a dose

MedlinePlus says to ask your doctor what to do if you miss a dose, and not to take a double dose to make up for it.

Storage

At room temperature in the original container, tightly closed, away from light, heat and moisture, out of reach of children. Throw away Zonisade 30 days after first opening, even if some is left, and use a take-back program rather than flushing.

Interactions to know about

Phenytoin, carbamazepine, phenobarbital and other drugs that speed up the liver enzyme CYP3A4 lower its levels. Topiramate, acetazolamide and other carbonic anhydrase inhibitors add to the risk of acidosis and kidney stones, and valproate or topiramate can add to the risk of high ammonia. A ketogenic diet adds to acidosis, and the label advises caution with alcohol and other medicines that depress the nervous system.

This summarizes the official prescribing information. Your prescriber’s and pharmacist’s instructions, and the leaflet that comes with your medicine, take priority.

Why the cash price for Zonisamide differs from pharmacy to pharmacy

Generic zonisamide capsules have many makers and cost pharmacies little, so quotes differ mainly by markup and dispensing fee, and the number of capsules matters: a dose of 300 or 400 mg a day is three or four 100 mg capsules. A prescription that names Zonegran and blocks substitution is priced as a brand.

Zonisade has no generic, so it is priced as a brand, and a pharmacy may need to order it. A bottle holds 150 mL and must be used within 30 days of opening, so the number of bottles a month depends on the dose.

Ways to pay less for Zonisamide without insurance

• Ask for generic capsules, and make sure the prescription allows substitution rather than naming Zonegran only.
• Once your dose is settled, ask for a ninety-day supply written with the fewest capsules per dose, such as one 100 mg capsule rather than four 25 mg capsules.
• Ask whether zonisamide is on the pharmacy’s flat-price generic list, and compare more than one pharmacy.
• If Zonisade is prescribed, ask the maker whether its savings or patient assistance program applies to someone paying cash, and ask the prescriber whether capsules would work for you.
• Upload the prescription to Script Unlock so licensed pharmacies can quote their cash price. You pay the pharmacy directly.

Questions to ask your pharmacist about Zonisamide

1. 1.I have reacted to a sulfa drug before; does that rule out zonisamide for me?
2. 2.When will my blood bicarbonate and kidney function be checked?
3. 3.How much should I drink each day to lower my risk of kidney stones?
4. 4.Does it interact with my topiramate, acetazolamide or other seizure medicines?

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