After reviewing the feasibility and projected completion date of the study, UCB has made the decision to stop the study

The purpose of the study is to evaluate the safety and tolerability, the pharmacokinetics and the efficacy of radiprodil in abolishing clinical spasms in subjects with drug-resistant infantile spasms

The study is divided into 3 parts:

Part A - exploratory, Part B - confirmatory, Part C - open label extension

Inclusion Criteria:

Part A and B:

• Subject is male or female between 2 and 14 months of age
• The diagnosis of infantile spasms (IS)
• Subject has drug-resistant IS

Part C:

• Subject participated in EP0078 Part A and received 2 radiprodil treatment cycles
• Subject experienced a relapse of spasms during the down taper or within 5 half-lives (3 days) discontinuation of radiprodil treatment in Cycle 2 of Part A
• Electroencephalogram (EEG) on baseline Part C is compatible with the diagnosis of infantile spasms

Exclusion Criteria:

Part A and B:

• More than 6 months have passed since the diagnosis of Infantile Spasms (IS)
• Current treatment with cannabinoids
• Subject has hematocrit greater than 60
• Subject has any medical condition that, in the opinion of the Investigator, could jeopardize or would compromise the subject's ability to participate in this study
• Subject has a history or current condition predisposing to respiratory dysfunction
• Current treatment with felbamate
• Current treatment with perampanel
• Ketogenic diet
• Clinically significant lab abnormalities
• Clinically significant abnormality on ECG that, in the opinion of the Investigator, increases the safety risks of participating in the study
• Subject has a lethal or potentially lethal condition other than IS, with a significant risk of death before 18 months of age such as non-ketotic hyperglycinemia
• Body weight is below 4 kg
• Known history of severe anaphylactic reaction secondary to medication intake or serious blood dyscrasias

Part C:

• Subject experienced any acute tolerability issues in either treatment cycle in Part A which the investigator and the sponsor medical monitor consider a risk for further participation
• Subject met any withdrawal criteria in Part A
• Subject has experienced any adverse effects or developed any new medical conditions since enrollment in Part A which the investigator considers could significantly increase the safety risks of participating in Part C