- Subject has a stable dose regimen of 1 to 3 marketed antiepileptic drug(s) (AEDs) with or without additional concurrent stable Vagus Nerve Stimulation (VNS). The VNS must have been in place for at least 6 months prior to study entry with constant settings for at least 28 days prior to the screening visit and during the Baseline Phase. Benzodiazepines will be counted as an AED