Zonisamide-induced behavior disorder in two children.

Zonisamide (ZNS)-induced behavior disorders are reported in a 1-year-old girl and a 3-year-old boy. Both patients, who had no previous developmental or mental problems, displayed secondarily generalized motor seizures. Serum concentrations of ZNS were not high, 8.8 and 12.3 micrograms/ml (effective range 10-30 micrograms/ml) respectively. Although many cases of ZNS-related psychotic reactions and/or behavior disorders have been reported, all affected patients had complex partial seizures (CPS) and had received combination therapy with phenytoin (PHT). Thus, whether the disorders were induced only by ZNS, by an interaction between ZNS and PHT, or by CPS could not be determined. In the children reported, however, ZNS clearly induced behavior disorders at plasma ZNS levels within or even below the therapeutic range.