Zonisamide: new drug. No advantage in refractory partial epilepsy.

Prescrire international 2007 Jun

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1) The first-line treatment for patients with partial epilepsy is carbamazepine monotherapy. Second-line options include monotherapy with valproic acid, gabapentin, lamotrigine or oxcarbazepine. Other antiepileptics are also available for combination therapy of refractory partial epilepsy. (2) Zonisamide is a sulphonamide derivative that inhibits carbonic anhydrase; it resembles topiramate, a drug already approved for use for this indication in the European Union. (3) The main clinical trial, a double-blind study lasting 36 weeks, compared the addition of zonisamide or placebo to ongoing treatment in 351 patients with refractory partial epilepsy. The "response rate" (the proportion of patients with at least a 50% reduction in the frequency of seizures) was significantly higher with zonisamide plus the previous treatment than with placebo plus the previous treatment (46.6% versus 17.6%). An indirect comparison suggests that this is no better than treatment with a second-line antiepileptic drug. (4) Results of three other placebo-controlled trials of third-line combinations in a total of 499 patients treated for 12 weeks were similar. (5) The main adverse effects of zonisamide are those typically seen with topiramate: neuropsychological disorders and disorders due to carbonic anhydrase inhibition (kidney stones, reduced perspiration, and hyperthermia). There are various other adverse effects, including a risk of severe skin rash. (6) The profile of interactions is complex. There is a risk of pharmacokinetic interactions, and of pharmacodynamic interactions with other carbonic anhydrase inhibitors. (7) In France, treatment with zonisamide costs nearly 20 times more than treatment with carbamazepine or valproic acid. (8) Zonisamide has no therapeutic advantages over other antiepileptics available for combination therapy of partial epilepsy.