Effects of methsuximide and mephenytoin on the behavior of pigeons under a repeated acquisition procedure.

Learning impairment is a potentially serious side effect of antiepilepsy medications. The present study investigated the effects of methsuximide and mephenytoin on learning in pigeons performing under a repeated acquisition procedure. Given acutely, methsuximide (25, 50, 75, and 100 mg/kg) and mephenytoin (60, 120, and 240 mg/kg) produced generally dose-dependent decreases in rates of responding. High doses of each drug increased overall errors; a within-session analysis of error distributions also indicated learning impairment.