Pronunciation: key-simp-ta
Generic name: ofatumumab
Dosage form: single-dose prefilled Sensoready pen for subcutaneous use (20 mg/0.4 mL), single-dose prefilled syringe for subcutaneous use (20 mg/0.4 mL)
Drug classes: CD20 monoclonal antibodies, Selective immunosuppressants

Medically reviewed by Carmen Pope, BPharm. Last updated on Jun 16, 2025.

What is Kesimpta?

Kesimpta is used to treat relapsing forms of multiple sclerosis (MS), including clinically isolated syndrome, relapsing-remitting disease, and active secondary progressive disease, in adults. It is self-administered once a month by subcutaneous injection after an initial dosing period. 

Exactly how Kesimpta works is unknown, but it is thought to involve binding to CD20, a protein present on pre-B and mature B lymphocytes (lymphocytes are a type of white blood cell that are more abundant in people with MS). Once bound to the B-cell, Kesimpta triggers the destruction of the cell. Clinical trials report that Kesimpta slows MS progression and reduces the rate of relapse, but it is not a cure. Kesimpta belongs to the drug class called CD20-directed cytolytic antibodies. It may also be called a selective immunosuppressant.

Kesimpta (ofatumumab) gained FDA approval on October 26, 2009. There is no generic or biosimilar. Kesimpta is not interchangeable with another brand of ofatumumab called Arzerra used for CLL.

Side effects

The most common side effects of Kesimpta are:

• upper respiratory tract infections with symptoms such as a sore throat, runny nose, and headache
• headache.

Serious side effects and warnings

Kesimpta can cause the following serious side effects:

• Infections. Serious infections, which can be life-threatening or cause death, can happen during treatment with Kesimpta. If you have an active infection, your healthcare provider should delay your treatment until your infection is gone. Kesimpta taken before or after other medicines that weaken the immune system may increase your risk of getting infections. Tell your healthcare provider right away if you have any infections or get any symptoms, including painful and frequent urination, nasal congestion, runny nose, sore throat, fever, chills, cough, or body aches.
  • Hepatitis B virus (HBV) reactivation. Before starting treatment, your healthcare provider will do blood tests to check for HBV. If you have ever had an HBV infection, the HBV may become active again during or after treatment. Hepatitis B virus becoming active again (called reactivation) may cause serious liver problems, including liver failure or death. You should not receive this medicine if you have active hepatitis B liver disease. Your healthcare provider will monitor you for HBV infection during and after you stop using this medicine.

Tell your healthcare provider right away if you get worsening tiredness or yellowing of your skin or the white part of your eyes during treatment.

• • Progressive Multifocal Leukoencephalopathy (PML). PML may happen with this medicine. PML is a rare, serious brain infection caused by a virus that may get worse over days or weeks. PML can result in death or severe disability. Tell your healthcare provider right away if you have any new or worsening neurologic signs or symptoms. These may include weakness on one side of your body, loss of coordination in arms and legs, vision problems, and changes in thinking and memory which may lead to confusion and personality changes.
  • Weakened immune system. Kesimpta taken before or after other medicines that weaken the immune system could increase your risk of getting infections.
• Injection-related reactions. Injection-related reactions are a common side effect of Kesimpta. These can happen within 24 hours (1 day) following the first injection and with later injections. There are 2 kinds of reactions:
  • at or near the injection site: redness of the skin, swelling, itching and pain. Talk with your healthcare
    provider if you have any of these signs and symptoms.
  • those that may happen when certain substances are released in your body: fever, headache, pain in the muscles, chills, tiredness, rash, hives, trouble breathing, swelling of the face, eyelids, lips, mouth, tongue and throat, and feeling faint, or chest tightness. Contact your healthcare provider right away if you experience any of these signs and symptoms, especially if they become worse or you have new severe signs of reactions after subsequent injections. It could be a sign of an allergic reaction, which can be serious.
• Low immunoglobulins. Kesimpta may cause a decrease in some types of antibodies. Your healthcare provider will do blood tests to check your blood immunoglobulin levels.

These are not all the possible side effects of Kesimpta. Call your healthcare provider for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

Related/similar drugs

Before using Kesimpta

Do not use Kesimpta if you:

• have an active hepatitis B virus infection
• have had an allergic reaction to ofatumumab, Kesimpta, or any of the inactive ingredients in the injection
• have had a life-threatening injection-related reaction to Kesimpta.

Before using this medicine, tell your healthcare provider about all of your medical conditions, including if you:

• have or think you have an infection including HBV or PML
• have ever taken, currently take, or plan to take medicines that affect your immune system. These medicines could increase your risk of getting an infection
• have had a recent vaccination or are scheduled to receive any vaccinations.
  • You should receive any required ‘live’ or ‘live-attenuated’ vaccines at least 4 weeks before you start treatment. You should not receive ‘live’ or ‘live-attenuated’ vaccines while you are being treated with this medicine and until your healthcare provider tells you that your immune system is no longer weakened.
  • Whenever possible, you should receive any ‘non-live’ vaccines at least 2 weeks before you start treatment with Kesimpta.
  • Talk to your healthcare provider about vaccinations for your baby if you used Kesimpta during your pregnancy.
• are pregnant, think you might be pregnant, or plan to become pregnant
• are breastfeeding or plan to breastfeed.

Pregnancy

It is not known if this medicine will harm your unborn baby. Females who can become pregnant should use birth control (contraception) during treatment with this medicine and for 6 months after your last treatment. Talk with your healthcare provider about what birth control method is right for you during this time.

Pregnancy Registry: There is a registry for women who become pregnant during treatment with Kesimpta. If you become pregnant while taking Kesimpta, tell your healthcare provider right away. Talk to your healthcare provider about registering with the MotherToBaby Pregnancy Study in Multiple Sclerosis.

The purpose of the registry is to collect information about your health and your baby’s health. For more
information or to register, contact MotherToBaby by calling 1-877-311-8972, by sending an email to MotherToBaby@health.ucsd.edu, or go to www.mothertobaby.org/join-study.

Breastfeeding

 It is not known if this medicine passes into your breast milk. Talk to your healthcare provider about the best way to feed your baby if you take this medicine.

How should I use Kesimpta?

See the detailed Instructions for Use that come with the Kesimpta Package Insert for information about how to prepare and inject a dose of this medicine and how to properly throw away (dispose of) used Sensoready pens or prefilled syringes.

• Use Kesimpta exactly as your healthcare provider tells you to use it.
• Kesimpta is given as an injection under your skin (subcutaneous injection), in your thigh or stomach area (abdomen) by you or a caregiver. A caregiver may also give you an injection in your upper outer arm. See Where and how is Kesimpta injected? for more information.
• Your healthcare provider will show you how to prepare and inject this medicine the right way before you use it for the first time.
• Do not inject into areas where the skin is tender, bruised, red, scaly, or hard. Avoid areas with moles, scars, or stretch marks.

Dosing information

Dosage of Kesimpta for relapsing forms of Multiple Sclerosis

• Weeks 0, 1, 2: 20 mg subcutaneously (SC) 
• Week 3: No injection
• Week 4 and monthly thereafter: 20 mg subcutaneously (SC) 

What happens if I miss a dose?

If you miss a monthly injection, give it as soon as possible without waiting until the next scheduled dose. After that, use your injections a month apart.

What other drugs will affect Kesimpta?

Tell your doctor about all your other medicines, especially drugs that weaken the immune system such as

• cancer medicine
• steroids
• medicines to prevent organ transplant rejection.

This list is not complete. Other drugs may affect Kesimpta, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible drug interactions are listed here. Tell your healthcare provider about all the medicines you take, including prescription and over-the-counter medicines, vitamins, and herbal supplements. Know the medicines you take. Keep a list of them to show your healthcare provider and pharmacist when you get a new medicine.

Storage

Store Kesimpta in a refrigerator between 36°F to 46°F (2°C to 8°C). Keep it in the original carton until ready for use to protect it from light.

If needed, Kesimpta may be stored for up to 7 days at room temperature, up to 86°F (30°C ). Write the date taken out of the refrigerator in the space provided on the carton.

If stored below 86°F (30°C), unused Kesimpta may be returned to the refrigerator and must be used within the next 7 days. If this Kesimpta is not used within those 7 days, then discard the medicine.

Do not freeze. Do not shake.

Keep out of the reach of children.

Ingredients

Active ingredient: ofatumumab
Inactive ingredients (pen and prefilled syringe): arginine, disodium edetate, polysorbate 80, sodium acetate trihydrate, sodium chloride, and Water for Injection. Hydrochloric acid may be added.

Available as:

• Single-dose prefilled Sensoready Pen 20 mg/0.4 mL
• Single-dose prefilled syringe 20 mg/0.4 mL.

Manufacturer

Kesimpta is made by Novartis, with its headquarters in Basel, Switzerland.

Kesimpta Biosimilars

Biosimilar and interchangeable products are biological products that are highly similar to and have no clinically meaningful differences from the reference product.

Reference products

These are biological products that have already been approved by the FDA, against which biosimilar products are compared. There are 2 for Kesimpta.

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Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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