A Study to Assess Vamorolone in Boys Ages 2 to <4 Years and 7 to <18 Years With Duchenne Muscular Dystrophy (DMD)

This Phase II study is an open-label, multiple dose study to evaluate the safety, tolerability, PK, PD, clinical efficacy, behavior and neuropsychology, and physical functioning of vamorolone administered orally at daily doses of 2.0 mg/kg and 6.0 mg/kg over a treatment period of 3 months in steroid-naïve boys ages 2 to \<4, and glucocorticoid-treated and currently untreated boys ages 7 to \<18 years with DMD.

The study is comprised of a 5-week Pretreatment Screening Period; a 1-day Pretreatment Baseline Period; a 3-month open-label Treatment Period (Weeks 1-12); and a 4-8 week open-label Dose-tapering Period (starting from Weeks 13) for subjects who will not transition directly to further vamorolone or standard of care (SoC) glucocorticoid treatment at the end of the study.

Subjects will be enrolled into the study at the Screening Visit, at the time written informed consent is obtained.

Within the 2 to \<4 years age group, the initial 10 eligible subjects will be assigned to the 2.0 mg/kg/day treatment group at the Baseline Day -1 Visit. The subsequent 10 eligible subjects will be assigned to the 6.0 mg/kg/day treatment group at the Baseline Day -1 Visit.

Within the 7 to \<18 years age group, both corticosteroid-treated and untreated, the initial 12 eligible subjects will be assigned to the 2.0 mg/kg/day treatment group at the Baseline Day -1 Visit. The subsequent 12 eligible subjects will be assigned to the 6.0 mg/kg/day treatment group at the Baseline Day -1 Visit.

The first 6 subjects in each age group at 2 mg/kg will serve as the PK/safety run-in cohorts. PK assessments will be performed at week 2 and together with the safety assessment during the first 4 weeks of treatment this will be the basis to confirm whether 2 and 6 mg/kg/day will be used in the subsequent patients or if a dose adjustment is needed to avoid over or under-exposure in patients for any of the two age groups.

Glucocorticoid-treated subjects in the 7 to \<18 years age group will take their final dose of SoC glucocorticoid therapy for DMD on Baseline Day -1, within 24 hours prior to administration of the first dose of vamorolone study medication.

All subjects in both age groups will begin their assigned vamorolone treatment on Treatment Period Day 1, and will continue to receive their assigned vamorolone treatment throughout the duration of the 3 month Treatment Period (Weeks 1-12).