A Study to Investigate the Efficacy and Safety of ZX008 (Fenfluramine Hydrochloride) as an Adjunctive Therapy in Children and Adults With Lennox-Gastaut Syndrome

Key Inclusion Criteria: * Male or non-pregnant, non-lactating female, age 2 to 35 years, inclusive as of the day of the Screening Visit. * Clinical diagnosis of Lennox-Gastaut syndrome, where seizures that result in drops are not completely controlled by current antiepileptic treatments. * Onset of seizures at 11 years of age or younger. * Abnormal cognitive development. * Must be receiving at least 1 concomitant AED and up to 4 concomitant anti-epileptic treatments. Key Exclusion Criteria: * 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. * I…