Inclusion Criteria:

• Be diagnosed with IS (regardless of etiology- except for a progressive neurologic illness). Diagnostic Criteria: Seizures consisting of single or repetitive short muscular contractions leading to flexion or extension. Spasms may be characterized as tonic or myoclonic contractions, may occur singly or in clusters, and typically occur bilaterally and symmetrically. The EEG pattern must be consistent with the diagnosis of IS (hypsarrhythmia, modified hypsarrhythmia, multifocal spike wave discharges, etc).
• Have a vEEG recording confirming the diagnosis of IS.
• Have had a magnetic resonance imaging (MRI) performed to determine any possible causes of IS.
• Have been previously treated with 3 or fewer AEDs.

• If being treated with concomitant AEDs

  • Current AEDs have been at a constant daily dose for at least 2 weeks; Note: Subjects with minor dose adjustments may be allowed to enter the study after shorter periods after detailed discussion with the medical monitor.
  • Have a stable clinical response/plateau for at least 2 weeks
  • Are able to continue treatment with no more than 2 concomitant AEDs (ACTH, corticosteroids, felbamate, and vigabatrin are not allowed concomitantly).
  • A ketogenic diet is permitted if it can be maintained for the duration of the study.
• Be a male or female, 4 to 24 months of age (inclusive)
• Have a Parent/Guardian who is properly informed of the nature and risks of the clinical study, who is willing and capable of complying with all clinical study procedures, and has given informed consent in writing prior to entering the clinical study
• Be able to participate for the full term of the clinical study.

Exclusion Criteria:

• Treatment with corticosteroids, ACTH, vigabatrin, felbamate, or any AED not approved by Regulatory Agencies, 2 weeks prior to randomization.
• Treatment with more than two AEDs at baseline.
• Have an active CNS infection, demyelinating disease, degenerative neurological disease, or CNS disease deemed progressive (with the exception of tuberous sclerosis) as evaluated by brain imaging (MRI).
• Have any disease or condition (medical or surgical) at screening that might compromise the hematologic, cardiovascular, pulmonary, renal, gastrointestinal, or hepatic systems; or other conditions that might interfere with the absorption, distribution, metabolism, or excretion of the investigational product, or would place the subject at increased risk.
• Aspartate aminotransferase (AST), alanine aminotransferase (ALT), or total bilirubin greater than four times the upper limit of normal (ULN) or clinical laboratory value deemed clinically significant by the Investigator.
• History of recurrent status epilepticus.
• Have been exposed to any other investigational drug within 30 days prior to randomization.