A Study to Learn About the Safety of Diroximel Fumarate (DRF) and Dimethyl Fumarate (DMF) and Their Effects on Relapses in Pediatric Participants With Relapsing Forms of Multiple Sclerosis (RMS)

The primary objectives of this study are to evaluate the safety, tolerability of diroximel fumarate (DRF), the noninferiority of the clinical efficacy of monomethyl fumarate (MMF) (pooled DRF and dimethyl fumarate [DMF] treatment) compared to that of fingolimod and long-term safety and tolerability of DRF in participants who completed Week 96 of the Treatment Period. The secondary objectives of this study are to characterize the pharmacokinetic (PK) profile of DRF metabolites (MMF and 2-hydroxyethyl succinimide [HES]), additional safety and tolerability of DRF, noninferiority of the radiological efficacy of MMF (pooled DRF and DMF treatment) compared to that of fingolimod, and to further describe the safety and long-term multiple sclerosis (MS) outcomes of DRF in participants who completed Week 96 of the Treatment Period.

Key Inclusion Criteria:

Treatment Period:

• Must have a diagnosis of pediatric MS (as defined by the revised consensus definition of pediatric MS).
• Must have an Expanded Disability Status Scale (EDSS) score between 0 and 5.0, inclusive.
• Must have experienced at least 1 of the following conditions:

• greater than or equal to 1 relapse in the 12 months prior to the Baseline Visit (Day 1),
• greater than or equal to 2 relapses in the 24 months prior to the Baseline Visit (Day 1), or
• evidence of gadolinium (Gd)-enhancing lesions of the brain on magnetic resonance imaging (MRI) within 6 months prior to the Baseline Visit (Day 1).
• Participants must be neurologically stable with no evidence of relapse within 30 days prior to the Baseline Visit (Day 1).

Open-Label Extension Period:

• Participants who completed the study treatment in Cohorts A or B through the Week 96 Visit.

Key Exclusion Criteria

Treatment Period:

• History of progressive MS.
• History of disorders mimicking MS, such as other demyelinating disorders (e.g., acute disseminated encephalomyelitis and neuromyelitis optical spectrum disorder), systemic autoimmune disorders (e.g., Sjögren's disease and lupus erythematosus), metabolic disorders (e.g., dystrophies), and infectious disorders.
• History of severe allergic or anaphylactic reactions or any allergic reactions that in the opinion of the Investigator are likely to be exacerbated by any component of the study treatment.
• History of, or ongoing, malignant disease, including solid tumors, skin malignancies, and hematologic malignancies.
• History of gastrointestinal (GI) surgery (except appendectomy or cholecystectomy that occurred more than 6 months prior to the Screening Visit), inflammatory bowel disease (Crohn's disease, ulcerative colitis), or another clinically significant and active GI condition at the Investigator's discretion.
• Known hypersensitivity to fumaric acid derivatives or any excipients of DRF or DMF.
• Diagnosis of macular edema prior to randomization.

Open-Label Extension Period:

• Any significant changes in medical history occurring after enrollment in the Treatment Period, including laboratory test abnormalities or current clinically significant conditions that, in the opinion of the Investigator, would have excluded the participant's participation in the Treatment Period. The Investigator must reassess the participant's medical fitness for participation and consider any factors that would preclude treatment.
• Participants who discontinued study treatment due to tolerability issues.
• Other unspecified reasons that, in the opinion of the Investigator or the Sponsor, make the participant unsuitable for participation in the OLE Period.

NOTE: Other protocol-defined Inclusion/Exclusion criteria may apply.