Zonisamide: a New Drug for Parkinson's Disease

Zonisamide, a benzisoxazole derivative, is an antiepileptic drug with a long half-life. Three nationwide, double-blind, placebo-controlled studies carried out in Japan prompted the approval of zonisamide as an antiparkinsonian agent in early 2009. The addition of zonisamide at 25-50 mg/day to currently used antiparkinsonian drugs significantly improved cardinal symptoms in patients with advanced Parkinson's disease. The effects were maintained over more than 1 year even in patients with advanced disease. Zonisamide has multiple modes of action, and its effects on Parkinson's disease include activation of dopamine synthesis, inhibition of monoamine oxidase, inhibition of T-type calcium channels and inhibition of an indirect pathway in the basal ganglia through the δ opioid receptor. Furthermore, zonisamide exhibits neuroprotective effects in animal models of Parkinson's disease. It strongly inhibits quinoprotein formation and markedly increases glutathione S-transferase levels in the striatum by enhancing the astroglial cysteine transport system and/or astroglial proliferation via S100beta production and secretion.