RMS stands for relapsing multiple sclerosis, a category of MS where symptoms flare up in episodes called relapses, then partially or fully fade during periods of remission. Kesimpta (ofatumumab) is an injectable medication approved to treat RMS by targeting immune cells that drive these attacks. Together, the search term refers to the disease Kesimpta is designed for and how the drug works to slow it down.
What Relapsing Multiple Sclerosis Includes
RMS is not a single diagnosis. It’s an umbrella term covering two related forms of MS. The first and most common is relapsing-remitting MS (RRMS), where you experience distinct flare-ups of neurological symptoms followed by recovery periods. During a relapse, inflammation damages the protective coating around nerve fibers in the brain and spinal cord, causing symptoms like vision problems, numbness, fatigue, or difficulty walking. Between relapses, symptoms may improve partially or completely.
The second form under the RMS umbrella is active secondary progressive MS (SPMS). Many people with RRMS eventually transition to SPMS, where disability gradually worsens over time even as full-blown relapses become less frequent. When SPMS still involves occasional relapses or new inflammatory activity visible on MRI, it qualifies as “active” SPMS and falls under the RMS category. Kesimpta is approved for both of these forms.
How Kesimpta Works
Kesimpta is a targeted antibody that depletes a specific type of immune cell called B-cells. In MS, certain B-cells become overactive and contribute to the inflammatory attacks that damage nerve insulation. These B-cells carry a surface marker called CD20, and Kesimpta locks onto that marker to flag the cells for destruction by the rest of the immune system.
Other MS therapies target the same CD20 marker, but Kesimpta binds to a different spot on it than older drugs in the same class. Once attached, it triggers multiple pathways that eliminate the problematic B-cells, reducing the immune system’s ability to launch the inflammatory attacks responsible for relapses and new brain lesions. Because it selectively targets CD20-positive B-cells rather than the entire immune system, it leaves other immune defenses more intact than broader immunosuppressants.
How Effective It Is
In pooled clinical trials comparing Kesimpta to another MS therapy (teriflunomide), Kesimpta reduced the risk of confirmed disability worsening at three months by about 34%, and by roughly 33% at six months. These numbers reflect sustained, measurable changes in disability rather than temporary symptom fluctuations, which makes them a meaningful gauge of long-term benefit. Kesimpta also significantly reduced the number of relapses and new inflammatory lesions on MRI in these same trials.
How You Take It
Unlike some other B-cell therapies that require IV infusions at a clinic, Kesimpta is a self-administered injection you give yourself at home using a prefilled pen similar to devices used for insulin or biologic medications for arthritis. The pen delivers a small, fixed dose under the skin of the thigh, abdomen, or outer upper arm.
The schedule starts with three weekly loading doses at weeks zero, one, and two. After a one-week break, you switch to once-monthly injections starting at week four. Each injection delivers 20 mg. For most people, the injection itself takes only seconds, though the first few doses carry a higher chance of injection-related reactions like redness, swelling, or mild pain at the site.
Side Effects and Safety Risks
The most common side effect is a reaction at the injection site: redness, pain, itching, or swelling where the needle went in. These reactions tend to be most noticeable with the first injection and generally become milder over time.
Because Kesimpta suppresses part of the immune system, it carries a few serious risks worth knowing about. The first is an increased susceptibility to infections. Upper respiratory infections, urinary tract infections, and other common illnesses may occur more frequently or take longer to resolve.
A rare but serious concern is progressive multifocal leukoencephalopathy (PML), a brain infection caused by a virus that can become active when the immune system is weakened. Symptoms to watch for include vision changes, loss of coordination, memory problems, difficulty speaking, or sudden leg weakness. PML is uncommon with Kesimpta, but it has occurred with other drugs in the same class.
Kesimpta can also reactivate hepatitis B in people who carry the virus, potentially causing liver damage. Symptoms of reactivation include yellowing of the skin or eyes, dark urine, pain on the right side of the abdomen, fever, or severe fatigue. This is why hepatitis B screening is required before starting the medication.
Testing Before You Start
Before your first dose, your doctor will order several baseline tests. Hepatitis B screening is mandatory, including tests for surface antigen and core antibody, because Kesimpta is not appropriate for anyone with active hepatitis B. Blood tests measuring your immunoglobulin levels (the antibodies your body uses to fight infections) are also required. If your levels are low, your doctor may consult with an immunology specialist before proceeding. Liver function blood work is checked as well to establish a baseline for monitoring during treatment.
These pre-treatment tests are not just formalities. They identify people who may face higher risks from immune suppression and help your medical team catch problems early if they develop after you begin treatment.