The inclusion and exclusion criteria for the patients who participated in lead-in Study 14362A will be transferred from the 14362A study and for the patients who did not participate in lead-in Study 14362A the inclusion/exclusion is separately listed below.

Inclusion Criteria:

1. The patient has a diagnosis of Dravet Syndrome supported by:
   1. onset of seizures in the first year of life
   2. history of fever-induced prolonged seizures as determined by the Investigator
      • these may include prolonged (approximately 15 minutes or longer) hemi-clonic seizures
   3. multiple seizure types which may include:
      • generalised tonic-clonic (required for inclusion)
      • clonic (required for inclusion)
      • myoclonic jerks/seizures
   4. history of normal development prior to seizure onset followed by development delay or regression after seizure onset
   5. abnormal EEG consistent with Dravet Syndrome
2. The patient is currently receiving a stable dose of clobazam of at least 0.5 mg/kg/day (maximum 20 mg/day) for at least 3 months

Exclusion Criteria:

1. The patient is taking stiripentol, verapamil, or felbatol. If patients have taken these drugs in the past, they need to have been off drug for 5 half-lives
2. The patient is taking a sodium channel blocker including but not limited to phenytoin, fosphenytoin, carbamazepine, oxcarbazepine, lamotrigine, lacosamide, and rufinamide. If patients have taken these drugs in the past, they need to have been off drug for 5 halflives
3. The patient must not have been on any benzodiazepine chronically (≥2 weeks for any indication) except clobazam for a period of at least 5 half-lives prior to screening
4. The patient is on cannabidiol, medical marijuana, or any drug that contains cannabinoids
5. The patient is currently taking long-term systemic steroids (>2 weeks)

Other protocol-defined inclusion and exclusion criteria may apply.