Key Points

• Kesimpta (ofatumumab) is an injectable medication that may be used to treat relapsing forms of multiple sclerosis. It belongs to a group of medications called anti-CD20 monoclonal antibodies.
• Common side effects of Kesimpta include upper respiratory tract infections, injection-related reactions, headache, injection-site reactions, urinary tract infection, and back pain.
• Serious allergic reactions can occur with any Kesimpta injection. It’s also possible to develop a life-threatening infection during treatment. Both require immediate medical attention.

What is Kesimpta?

Kesimpta (ofatumumab) is an FDA-approved anti-CD20 monoclonal antibody used to treat relapsing forms of multiple sclerosis (MS) in adults. It works by targeting and reducing B-cells, which are believed to contribute to MS-related inflammation. Kesimpta is administered as a monthly under-the-skin injection after an initial dosing period.

8 side effects of Kesimpta and how to manage them

Here are eight side effects* of Kesimpta that you should be aware of, along with management tips to help you continue treatment smoothly.

1. Upper respiratory tract infection

Kesimpta can affect part of your immune system, making it more difficult to fight off infections. Upper respiratory tract infections occur in around 39% of people who take Kesimpta. These include the common cold, influenza, and sinus infections. Most of the time, these infections get better on their own within a few days or weeks.

Tips for managing upper respiratory tract infection

• Get plenty of rest to help your body fight off the infection
• Stay hydrated with water, tea, and broth to help loosen mucus
• Use over-the-counter fever reducers, decongestants, or pain relievers to help with your symptoms
• Run a cold-mist humidifier in your sleeping room to moisten the air and soothe your airways
• Gargle salt water if you have a sore throat

Contact your doctor if you notice signs of infection such as fever, cough, sore throat, body aches, sinus pain, or chills. They can make sure it’s still safe for you to continue to take Kesimpta. You might need to delay your treatment if your infection is severe.

2. Injection-related reactions

Injection-related reactions are a common side effect from taking Kesimpta. These reactions include fever, headache, muscle pain, chills, and fatigue. They usually happen within 24 hours of the first injection. This is why your doctor will supervise your first injection. However, it’s possible to experience injection-related reactions after later injections too.

Tips for managing injection-related reactions

• Use an over-the-counter pain reliever to treat headache, muscle pain, and fever
• Rest until your energy returns
• Use a warm or cold compress on your forehead to relieve headache

Most injection-related reactions that occur after taking Kesimpta are mild or moderate, and not life-threatening. It can be difficult to know the difference between an injection-related reaction and an allergic reaction. If your symptoms are getting worse, or if you have new severe signs of reactions after later injections, this could be an allergic reaction. If this happens, get medical help right away. Tell your prescriber if you notice any reactions after injecting a dose of Kesimpta.

3. Headache

It’s common to experience a headache while taking Kesimpta. Around 13% of people taking Kesimpta during studies reported it as a side effect. Headaches can usually be treated at home. However, if your headache seems severe or isn’t going away, you should get medical attention.

Tips for managing headaches

• Drink plenty of fluids throughout the day
• Decrease the noise in your environment
• Rest in a dark room
• Try some relaxation techniques, like deep breathing, yoga, or meditation
• Use over-the-counter pain relievers to manage pain
• Apply a warm or cold compress to your forehead

4. Injection-site reactions

Injections can sometimes cause pain, redness, swelling, and itching afterward, including Kesimpta. You might notice one or more of these symptoms near the place where you injected your dose. They usually get worse during the first day, and then improve within a few days. Most of the time, injection-site reactions can be managed at home.

Tips for managing injection-site reactions

• Apply an ice pack for 10 to 15 minutes to reduce swelling
• Use an anti-itch medication around the injection site
• Try an over-the-counter pain reliever, like ibuprofen (Advil), to help with pain and swelling

If your symptoms aren’t getting better within a few days or continue to get worse, talk to your doctor. They can rule out more serious conditions, like a skin infection.

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5. Urinary tract infection

Another common side effect of Kesimpta is urinary tract infection (UTI), with 10% of people getting at least one during treatment. If you notice pain or burning when you urinate, the urge to go to the bathroom more often, cloudy urine, or urine that smells strange, you might have a UTI. A fever, chills, or feeling tired is more common with severe infections. If you suspect that you have a UTI, it’s important to consult your doctor and get treatment if needed.

Tips for preventing urinary tract infections

• Don’t hold it in - go to the bathroom as soon as you feel the urge
• Always wipe from front to back after using the toilet
• Avoid feminine products such as douches or deodorant sprays
• Urinate after sex to flush out any bacteria that may have entered the urethra
• Drink plenty of fluids
• Take showers instead of baths

6. Back pain

Back pain is common in people with multiple sclerosis (MS). This might be due to weakness in the legs, or stiff muscles caused by MS. In a systematic review of 14 studies, up to 52% of people with MS reported experiencing back pain.

In studies of Kesimpta, 8% of people reported back pain as a side effect. While it isn’t clear if this is truly a side effect of Kesimpta or a symptom of MS, there are some things you can do to feel better.

Tips for managing back pain

• Practice good posture
• Maintain a healthy weight
• Wear supportive footwear
• Try an over-the-counter pain reliever
• Apply heat or cold therapy
• Do stretches from a physical therapist to improve muscle strength in your back

Sometimes, back pain can be a sign of an infection or another serious medical condition. If your back pain isn’t getting better or seems severe, contact your doctor for further evaluation.

7. Severe allergic reaction

Severe allergic reactions can occur after any injection of Kesimpta. If you notice hives, swelling in your face, trouble breathing, or difficulty swallowing, get medical attention right away. Your doctor will need to stop Kesimpta and switch you to a different medication.

8. Life-threatening infections

Serious fungal, bacterial, or viral infections can occur in people taking anti-CD20 B-cell depleting medications like Kesimpta. This is because these medications weaken part of your immune system, which makes it harder to fight off infections. Some of these infections can be life-threatening or fatal.

In clinical studies of Kesimpta, the most common infections were upper respiratory tract infections and urinary tract infections. However, reactivation of previous infections (e.g., hepatitis B) or getting a serious brain infection called progressive multifocal leukoencephalopathy is a risk with treatments like Kesimpta.

In a long-term study that followed people taking Kesimpta for up to 3.5 years, the incidence of serious infections was low. It’s recommended to get all appropriate live vaccines at least 4 weeks before starting Kesimpta and inactivated vaccines at least 2 weeks before to help lower your risk of infections.

It’s important to contact your doctor right away if you have any signs of an infection, such as fever, chills, cough, or pain with urination. Also let them know if you notice weakness on one side of your body, vision changes, confusion, or personality changes. They can determine if you have an infection and recommend an appropriate treatment.

* This is not a complete list of side effects. See here for more information.

References

Kesimpta [package insert]. Revised 04/2024. Novartis Pharmaceuticals Corporation - https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=6a8a3f53-2062-48ff-9dbe-b939df133ca3

De Seze, J., et. al. (2023). Anti-CD20 therapies in multiple sclerosis: From pathology to the clinic. In: Frontiers in Immunology. Available from: https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2023.1004795/full

Hauser, S., et. al. (2022). Safety experience with continued exposure to ofatumumab in patients with relapsing forms of multiple sclerosis for up to 3.5 years. In: Multiple Sclerosis. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9330270/

Massot, C., et. al. (2020). Low back pain in patients with multiple sclerosis: A systematic review and the prevalence in a French multiple sclerosis population. In: Revue Neurologique. Available from: https://pubmed.ncbi.nlm.nih.gov/33032798/

National Multiple Sclerosis Society. (n.d.). Pain and Itching. Accessed 05/12/2024. Available from: https://www.nationalmssociety.org/understanding-ms/what-is-ms/ms-symptoms/pain-itching

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Drug information

• Kesimpta Information for Consumers
• Kesimpta prescribing info & package insert (for Health Professionals)
• Side Effects of Kesimpta (detailed)
• Kesimpta user reviews (77)

Related support groups

• Kesimpta (7 questions, 3 members)
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