Inclusion Criteria:

• Subject must be male or non-pregnant, non-lactating female, age 2 to 18 years (inclusive)
• Subject must have documented medical history to support a clinical diagnosis of Dravet syndrome, where convulsive seizures are not completely controlled by current antiepileptic drugs.
• Subject must be receiving a therapeutically relevant and stable dose of CLB, VP, and STP for at least 4 weeks prior to screening and are expected to remain stable throughout the study (Cohort 2 only).
• Subject must be receiving a stable dose of CLB and VPA, administered twice daily, to be eligible for Dose Regimen 1 and 2 or subject must be receiving a stable dose of CLB, VPA, and STP, administered twice daily, to be eligible for Dose Regimen 3 (Cohort 1 only).

Exclusion Criteria:

• Subject has a known hypersensitivity to fenfluramine or any of the excipients in the study medication.
• Subject has pulmonary arterial hypertension.
• Subject has a current or past history of cardiovascular or cerebrovascular disease, such as cardiac valvulopathy, myocardial infarction or stroke.
• Subject has a current or recent history of anorexia nervosa, bulimia, or depression within the prior year that required medical treatment or psychological treatment for a duration greater than 1 month.
• Subject has a current or past history of glaucoma.
• Subject is receiving concomitant therapy with: centrally-acting anorectic agents; monoamine-oxidase inhibitors; any centrally-acting compound with clinically appreciable amount of serotonin agonist or antagonist properties, including serotonin re-uptake inhibition; triptans, atomoxetine, or other centrally-acting noradrenergic agonist; cyproheptadine, and/or CYP 2D6/3A4/2B6 inhibitors/substrates.
• Subject is currently taking carbamazepine, oxcarbamazepine, eslicarbazepine, phenobarbital, or phenytoin, or has taken any of these within the past 30 days, as maintenance therapy.
• Subject has a positive result on urine THC Panel or whole blood CBD at the Screening Visit.
• Subject has 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.