• Etiology of seizures is a degenerative neurological disease. • History of hemiclonic seizures in the first year of life. • Subject only has drop seizures in clusters, where individual seizures cannot be counted reliably. • Pulmonary arterial hypertension. • Current or past history of cardiovascular or cerebrovascular disease, such as cardiac valvulopathy, myocardial infarction or stroke. • Receiving concomitant therapy with: centrally-acting anorectic agents; monoamineoxidase inhibitors; any centrally-acting compound with clinically appreciable amount of serotonin agonist or antagonist properties, including serotonin reuptake inhibition; atomoxetine, or other centrally-acting noradrenergic agonist; cyproheptadine. • Taking felbamate for less than 1 year prior to screening and/or does not have stable liver function and hematology laboratory tests, and/or the dose has not been stable for at least 60 days prior to the Screening Visit. • Currently receiving an investigational product. • Institutionalized in a general nursing home (ie, in a facility that does not specialize in epilepsy care). • A clinically significant condition, or has had clinically relevant symptoms or a clinically significant illness in the 4 weeks prior to the Screening Visit, other than epilepsy, that would negatively impact study participation, collection of study data, or pose a risk to the subject.