Prescription ·Strong evidence ·Reviewed May 2026
Zonisamide is an antiseizure medication used for focal-onset seizures. It is a sulfonamide and carbonic anhydrase inhibitor, so serious rash, metabolic acidosis, kidney stones, oligohidrosis, and heat illness are key safety concerns. Folate lowering has been reported with some antiseizure therapies, and bicarbonate monitoring is clinically important because zonisamide can reduce serum bicarbonate.
The bottom line
Evidence rating strong. Most-documented uses: adjunctive treatment of focal-onset seizures, reduction in seizure frequency, once-daily or twice-daily dosing because of long half-life. 3 sources indexed (2002–2026), with 4 interaction records on file.
Core mechanism
Zonisamide appears to reduce seizure activity through voltage-gated sodium-channel blockade, T-type calcium-channel effects, and carbonic anhydrase inhibition. Carbonic anhydrase inhibition can cause renal bicarbonate loss and chronic metabolic acidosis, increasing risk of kidney stones and bone effects. Sulfonamide-related hypersensitivity can lead to severe skin, hepatic, hematologic, or multiorgan reactions.2,3
May be taken with or without food. Adequate hydration is important to reduce kidney stone risk.2
Nutrients this medication can lower over time, and what to replace.
Carbonic anhydrase inhibition increases renal bicarbonate loss, producing a non-anion-gap metabolic acidosis with reduced serum bicarbonate.
Long-term antiseizure therapy has been associated with reduced folate status in some patients; the evidence is stronger for older enzyme-inducing drugs but folate monitoring is reasonable when risk factors or deficiency signs are present.
High-dose vitamin C can increase urinary oxalate in some patients. Zonisamide increases kidney stone risk.
Recommendation: Avoid high-dose vitamin C in patients with kidney stone history or zonisamide-related stone risk unless approved by the clinician.
Potassium citrate or alkali therapy may be used medically for acidosis or stones, but unsupervised potassium can be unsafe.
Recommendation: Use potassium-containing alkali only under clinician guidance with electrolyte and kidney monitoring.
Ginkgo has seizure case reports and may undermine antiseizure therapy.
Recommendation: Avoid ginkgo in people using zonisamide for seizures unless the neurologist approves.
Melatonin can add to zonisamide-related somnolence, dizziness, or cognitive slowing.
Recommendation: Use cautiously and monitor next-day alertness.
Numbered references. Citations throughout the page link here.
Review discusses folate considerations in people receiving long-term antiseizure therapy.
Capsule labeling reports a plasma half-life of about 63 hours and cautions that steady state may take up to 2 weeks after dose changes.
Labeling specifies 100 mg daily initiation, metabolic acidosis warnings, sulfonamide reactions, kidney stones, and hydration considerations.
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