This is a phase II clinical trial in which children with refractory infantile spasms (also called epileptic spasms or West syndrome) will be treated with fenfluramine, to evaluate efficacy, safety, and tolerability. Patients with infantile spasms that have not responded to treatment with vigabatrin and ACTH we will be invited to participate. Study participants will undergo baseline video-EEG, receive treatment with fenfluramine for 21 days, and then undergo repeat video-EEG to determine effectiveness. Patients with favorable response will have the opportunity to continue treatment for up to 6 months.

Inclusion Criteria:

• Children ages 12 to 36 months, inclusive
• Clinical diagnosis of infantile spasms
• Continued epileptic spasms despite adequate treatment with ACTH and vigabatrin.

Exclusion Criteria:

• Significant preexisting cardiovascular disease
• Exposure to any cannabinoid product within 14 days of screening
• Initiation or dose-titration of any second-line treatment for infantile spasms in the 14 days prior to screening.
• Implantation of a vagal nerve simulator within 14 days of screening
• Initiation and maintenance of the ketogenic diet within 3 months of screening