Key Inclusion Criteria:

• Subject must have been <11 years of age at the onset of LGS
• Subject must have LGS
• Subject must be on at least 1 antiepileptic drug (AED).
• Parent or caregiver must be able to keep an accurate seizure diary.

Key Exclusion Criteria:

• Etiology of subject’s seizures is a progressive neurologic disease. Subjects with tuberous sclerosis will not be excluded from study participation.
• Subject has had an episode of status epilepticus within 12 weeks of baseline.
• Subject has had an anoxic episode requiring resuscitation within 1 year of screening.
• Subject has a history of an allergic reaction or significant sensitivity to benzodiazepines.
• Subject is taking more than 3 concurrent AEDs. Note: VNS or ketogenic diet is allowed and each will be counted as one of the three allowed AEDs.
• If the subject is on the ketogenic diet, has been for less than 4 weeks prior to screening or suffers from frequent stooling.
• If the subject has a VNS, the settings have not been stable for at least 4 weeks prior to screening.
• Subject has taken corticotropins in the 6 months prior to screening.
• Subject is currently taking long-term systemic steroids (excluding inhaled medication for asthma treatment) or any other daily medication known to exacerbate epilepsy. An exception will be made of prophylactic medication, for example, for urinary tract infections or asthma.
• If the subject is taking felbamate, has been taking it for less than 1 year prior to screening or previous treatment with felbamate resulted in withdrawal due to liver or bone marrow adverse events.