- Subject must have been observed to have Partial-Onset Seizures for at least the previous 2 years despite prior therapy with at least 2 Anti-Epileptic Drugs (AEDs)(concurrently or sequentially) and must have been observed to have on average at least 4 Partial-Onset Seizures per 28 days with a seizure-free phase no longer than 21 days in the 8-Week Period prior to entry into the Baseline Period. In the case of Simple Partial Seizures, only those with motor signs will be counted towards meeting the inclusion criterion