A Pharmacokinetics (PK), Pharmacodynamics (PD), Safety and Tolerability Study of Fenebrutinib in Children and Adolescents With Relapsing Multiple Sclerosis (RMS)

This study is testing a drug called fenebrutinib in children and teenagers who have relapsing multiple sclerosis (MS) — a condition where the immune system attacks the nervous system, causing episodes of symptoms that come and go. The study looks at how the drug moves through the body and whether it is safe for young people. **You may be eligible if...** - You are a child or adolescent diagnosed with relapsing MS - You have had at least one MS flare-up in the past year, or two in the past two years, or an active lesion on MRI - Your disability level falls within an accepted range on a standard MS scale - You are up to date on all recommended childhood vaccines **You may NOT be eligible if...** - You have a type of MS that is primarily progressive (never gets better) - You have significant other neurological, psychiatric, or serious medical conditions - You have had cancer, an organ transplant, or a bleeding disorder - You cannot have an MRI - You are currently on certain MS medications or immune-suppressing drugs - You are pregnant or at significant risk of suicide Talk to your doctor to see if this trial is right for you.