Antiepileptic with multiple mechanisms
ATC code: N03AX15 (Zonisamide)
A sulfonamide derivative with multiple mechanisms: voltage-gated sodium channel and T-type calcium channel blockade, weak carbonic anhydrase inhibition. Also modulates GABAergic and dopaminergic transmission. Compared with other antiepileptics, has a long half-life (60 hours) allowing once or twice daily dosing. CYP3A4-metabolized.
Second line
Second-line in focal epilepsy in adults and children over 6, as monotherapy or combination per ILAE 2017 and SEN 2024. First-line is lamotrigine, levetiracetam, lacosamide. Starting dose 50 mg once daily, titrated to 300–500 mg daily. Long half-life provides stable concentration.
The drug is promoted for these uses outside international guidelines. Each entry below is analyzed against AEMPS, FDA, EMA, Cochrane and major RCTs.
Not recommended
Zonisamide is a sulfonamide-class antiepileptic. It is prescribed for focal epilepsy and Lennox-Gastaut syndrome ( 2018, AEMPS Ficha Técnica). Zonisamide is used off-label for weight loss based on the weight-loss side effect. In people without epilepsy, zonisamide is not approved for weight loss. The drug has serious risks: severe skin reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis, DRESS), nephrolithiasis (kidney stones), metabolic acidosis, oligohidrosis with heat stroke risk, cognitive disturbances, depression, and suicidal ideation. If zonisamide was prescribed for weight loss, consider seeking a second opinion.
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T1 use raises malformation risk (cleft lip/palate, cardiac defects) 2–3 fold. In pregnant epilepsy patients, decisions are made with an epileptologist; switch to lamotrigine or levetiracetam.
High milk concentrations. Use during lactation cautiously with monitoring of infant sedation and weight gain.
Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.
Zonisamide is evaluated for the following indications with varying evidence strength: Focal epilepsy (evidence tier A), Weight loss (evidence tier F). See the full indication matrix with dosing and citations above on this page.
Common side effects of Zonisamide (≥ 1 in 100): Drowsiness, Dizziness, Ataxia, Anorexia and weight loss, Paraesthesia, Cognitive impairment. See the Safety section for uncommon and serious reactions.
FDA category C. T1 use raises malformation risk (cleft lip/palate, cardiac defects) 2–3 fold. In pregnant epilepsy patients, decisions are made with an epileptologist; switch to lamotrigine or levetiracetam.
High milk concentrations. Use during lactation cautiously with monitoring of infant sedation and weight gain.
Zonisamide is contraindicated in: Hypersensitivity to zonisamide or sulfonamides; Severe hepatic or renal impairment; Pregnancy – with caution; Age under 6. Full list in the Safety section.