Kesimpta (ofatumumab) is a prescription medication used to treat relapsing forms of multiple sclerosis (MS) in adults. It was approved by the FDA for three specific subtypes: clinically isolated syndrome (a first episode of MS-like symptoms), relapsing-remitting MS, and active secondary progressive MS. It belongs to a class of drugs that work by targeting and depleting certain immune cells involved in the nerve damage MS causes.
How Kesimpta Works
MS occurs when the immune system mistakenly attacks the protective coating around nerve fibers in the brain and spinal cord. B cells, a type of white blood cell, play a key role in driving this damage. Kesimpta is a fully human monoclonal antibody that latches onto a protein called CD20, which sits on the surface of B cells. Once it binds, it flags those B cells for destruction, effectively clearing them from circulation.
By reducing the number of these harmful B cells, Kesimpta lowers the immune system’s ability to launch attacks on nerve tissue. Studies using blood tests to track B cell levels show that the percentage of circulating B cells drops significantly within the first month of treatment and stays suppressed at 3, 6, and 12 months.
What the Clinical Trials Showed
Kesimpta’s approval was based on the ASCLEPIOS I and II phase 3 trials, which enrolled over 600 patients with early relapsing MS who had not been treated before. Compared with teriflunomide (an older oral MS drug), Kesimpta cut the annualized relapse rate by about 50%, bringing it down from 0.18 relapses per year to 0.09. That’s roughly half as many flare-ups over the course of a year.
The trials also tracked disability progression. Patients on Kesimpta had a 46% lower risk of confirmed disability worsening at six months compared with those on teriflunomide. At the three-month mark, the reduction was 38%, though that result didn’t quite reach statistical significance. These numbers suggest Kesimpta not only reduces relapses but also slows the accumulation of long-term disability, which is one of the most important goals in MS treatment.
How It’s Given
One of Kesimpta’s distinguishing features is that it’s a self-administered injection you give yourself at home using a prefilled autoinjector pen. You inject it under the skin of the thigh, abdomen, or outer upper arm. This sets it apart from a closely related drug, Ocrevus (ocrelizumab), which also targets CD20 but requires an intravenous infusion at a medical facility every six months.
Treatment starts with a loading phase: one injection per week for the first three weeks (at weeks 0, 1, and 2). After that, you skip a week and then move to one injection per month for as long as you stay on the medication. Your first injection is typically done under the guidance of a healthcare provider so you can learn the technique and be monitored for any immediate reactions.
Side Effects
The most commonly reported side effects are injection site reactions and upper respiratory infections like colds and sinus infections. Injection reactions tend to be most noticeable after the very first dose and often become milder or disappear entirely with subsequent injections. Symptoms can include redness, pain, itching, or swelling at the injection site, along with fever, headache, or muscle aches.
Because Kesimpta suppresses B cells, it lowers part of your immune defense. This means infections can occur more easily or be harder to shake. Signs to watch for include prolonged fevers, unusual fatigue, painful urination, or a cough that won’t clear up. In rare cases, serious allergic reactions including difficulty breathing and facial swelling have been reported.
Shingles (caused by reactivation of the chickenpox virus) is another known risk. Painful blisters on the trunk of the body are the hallmark symptom. Your doctor may recommend vaccination against shingles before you start treatment, since live vaccines shouldn’t be given once you’re on the drug.
Screening Before You Start
Before your first dose, your healthcare team will run several tests. Hepatitis B screening is required because drugs that deplete B cells can reactivate a dormant hepatitis B infection, which can be dangerous. You’ll also have your immunoglobulin levels checked through a blood test to make sure your baseline immune function is adequate. Additional tests your provider may order include a complete blood count, liver and kidney function panels, tuberculosis screening, and a urinalysis.
Storage and Handling
Kesimpta pens need to be kept in the refrigerator between 36°F and 46°F. If you need to travel or don’t have refrigerator access, the pen can sit at room temperature (up to 86°F) for up to 7 days. An unused pen that’s been at room temperature can go back in the fridge, but it must then be used within 7 days or discarded. Keeping the pen in its original carton protects it from light.
How Kesimpta Compares to Other MS Treatments
Kesimpta occupies a unique space in the MS treatment landscape. It’s a high-efficacy therapy, meaning it’s among the most effective options available, but it doesn’t require clinic visits for infusions. For people who want the potent B cell depletion that drugs like Ocrevus provide but prefer the convenience of a monthly at-home injection, Kesimpta fills that gap. Both drugs target the same protein on B cells and belong to the same therapeutic class, so their effectiveness profiles are broadly similar. The main practical difference is the route: a self-injection pen versus an IV infusion every six months.
Compared to older oral or injectable MS therapies, Kesimpta’s 50% reduction in relapse rate in treatment-naive patients represents a meaningful step up in efficacy. This is why many neurologists now consider it a first-line option for patients with active relapsing MS, rather than reserving it for people who haven’t responded to milder treatments.