Zonisamide

Zonisamide (brand name Zonegran®) is a sulfonamide anticonvulsant approved for use as an adjunctive therapy in adults with partial-onset seizures. It was discovered by researchers at Dainippon Sumitomo Pharma (大日本住友製薬: Dainippon Sumitomo Seiyaku (formerly Dainippon Pharmaceutical (大日本製薬: Dainippon Seiyaku)), who launched it in 1989 as Excegran® in Japan. It was marketed by Élan in the United States starting in 2000 as Zonegran®, before Élan transferred their interests in zonisamide to Eisai (エーザイ) in 2004. more...

Eisai also markets Zonegran® in Asia (China, Taiwan, and fourteen others) and Europe (starting in Germany and the United Kingdom).

Uses

Approved

Zonisamide is approved in the United States, United Kingdom, and Japan for adjunctive treatment of partial seizures in adults.

Unapproved/Off-Label/Investigational

An open trial on zonisamide in seven Parkinson's disease patients had positive results, according to this 2001 report. Since then, it has been reported to treat the resting tremor that other therapies may leave behind. By early November of 2005, Dainippon Sumitomo had filed a NDA for the use of zonisamide in Parkinson's disease; it is to be marketed as Tremode®.

Metabolism

Zonisamide is metabolized mostly by the CYP3A4 isoenzyme, but also CYP3A7 and CYP3A5, to 2-(sulphamoylacetyl)-phenol via reductive cleavage of the 1,2-benzisoxazole ring.

Mechanism of Action

The exact mechanism of action is not known for zonisamide. According to Leppik, while zonisamide may be a carbonic anhydrase inhibitor like acetazolamide, this is not one of the primary mechanisms of action, which might be blocking repetitive firing of voltage-gated sodium channels and reduction of T-type calcium channel currents, or by binding allosterically to GABA receptor like the benzodiazepines and muscimol, or increasing the levels of the glutamate transport protein in the brain while decreasing the amount of GABA transport protein, in other words, inhibiting the uptake of the inhibitory neurotransmitter GABA while enhancing the uptake of the excitatory neurotransmitter glutamate.

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