A 2-Part Study to Investigate the Dose-Ranging Safety and Pharmacokinetics, Followed by the Efficacy and Safety of ZX008 (Fenfluramine Hydrochloride) Oral Solution as an Adjunctive Therapy in Children ≥ 2 Years Old and Young Adults With Dravet Syndrome

The primary purpose of this study is to evaluate the safety, tolerability, and efficacy of ZX008 (fenfluramine hydrochloride) when added to adjunctive antiepileptic stiripentol treatment in children and young adults with Dravet syndrome.

This is a multicenter, 2-cohort trial to first assess the pharmacokinetic and safety profile of a single dose of ZX008 (fenfluramine hydrochloride) oral solution when added to a standard Dravet syndrome treatment regimen containing valproate (VPA) and clobazam (CLB), with or without stiripentol (STP) (Cohort 1), followed by a randomized, double-blind, placebo-controlled parallel group evaluation of the efficacy, safety, and tolerability of ZX008 as adjunctive therapy for seizures in children and young adults with Dravet syndrome (Cohort 2).

Eligibility Criteria:
Key Inclusion Criteria:

* Subject must be male or non-pregnant, non-lactating female, aged 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 stiripentol (STP) plus clobazam (CLB) and/or valproate (VPA), and for at least 4 weeks prior to screening and be expected to remain stable throughout the study (Cohort 2 only).
* Subject must be receiving a stable dose of CLB and VPA, administered twice daily (BID), to be eligible for Dose Regimen 1 and 2, or subject must be receiving a stable dose of CLB, VPA, and STP, administered BID, to be eligible for Dose Regimen 3 (Cohort 1 only).

Key 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 reuptake inhibition; triptans, atomoxetine, or other centrally acting noradrenergic agonists; cyproheptadine, and/or cytochrome P450 (CYP) 2D6/3A4/2B6 inhibitors/substrates.
* Subject is currently taking carbamazepine ,oxcarbazepine, 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 tetrahydrocannabinol (THC) panel or whole blood cannabidiol (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.