Kesimpta (ofatumumab) is a brand-name subcutaneous injection prescribed for multiple sclerosis (MS) and clinically isolated syndrome. As with other drugs, Kesimpta can cause side effects, such as upper respiratory infections and injection site reactions.

Kesimpta can cause certain side effects, some of which are more common than others. These side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

These are just a few of the more common side effects reported by people who took Kesimpta in clinical trials:

* For more information about this side effect, see “Side effect specifics.”

Mild side effects can occur with Kesimpta use. This list doesn’t include all possible mild side effects of the drug. For more information, you can refer to Kesimpta’s prescribing information.

Mild side effects that have been reported with Kesimpta include:

These side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks side effects of the medication. If you develop a side effect during Kesimpta treatment and want to tell the FDA about it, visit MedWatch.

* For more information about this side effect, see “Side effect specifics.”

Kesimpta may cause serious side effects. The following list may not include all possible serious side effects of the drug. For more information, you can refer to Kesimpta’s prescribing information.

If you develop serious side effects during Kesimpta treatment, call your doctor right away. If the side effects seem life threatening or you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Serious side effects that have been reported and their symptoms include:

* For more information about this side effect, see “Side effect specifics.”

Kesimpta may cause several side effects. Here are some frequently asked questions about the drug’s side effects and their answers.

Is Kesimpta chemotherapy?

No, Kesimpta is not a chemotherapy drug. It’s an immunosuppressant drug that works by reducing the activity of some parts of the immune system. This can help reduce MS symptoms.

Chemotherapy works by killing cells that multiply rapidly, which includes cancer cells. Some chemotherapy drugs are used to treat MS, such as mitoxantrone.

Will I have hair loss with Kesimpta?

Hair loss was not reported as a side effect of Kesimpta in clinical trials of the drug.

However, hair thinning and hair loss have been reportedTrusted Source to an FDA database by people having other MS treatments. These reports are voluntary and do not include each person’s full medical history. This means it’s not known for sure whether the MS treatments caused the hair loss. It’s also not possible to determine how common this side effect is.

If you’re concerned about hair loss, talk with your doctor. They can suggest ways to help prevent or manage hair loss.

Which lab tests will I need to have done before starting Kesimpta treatment?

Before you start Kesimpta, you’ll have a blood test to check for an active or past HBV infection. The HBV test is done before starting Kesimpta because the drug reduces your immune system’s ability to fight infections. If you’ve had HBV in the past, this treatment may cause reactivation of the infection. This means the virus may become active and cause symptoms again.

HBV reactivation was not seen in clinical trials of Kesimpta for treating MS. However, HBV reactivation did occur in clinical trials involving people with chronic lymphocytic leukemia who took ofatumumab (the active drug in Kesimpta).

If your test is positive for HBV, your doctor may recommend another MS treatment option for you. If they recommend that you start Kesimpta despite the positive test result, they may monitor your liver function on a routine basis.

Learn more about some of the side effects that Kesimpta may cause. To find out how often side effects occurred in clinical trials, see the prescribing information for Kesimpta.

Injection-related side effects

Injection-related reactions may occur with Kesimpta. These reactions were common in clinical trials of Kesimpta.

Injection-related reactions are body-wide reactions that often happen within the first 24 hours after your injection. They are more common with the first injection (first dose of Kesimpta) than with subsequent injections. Injection-related side effects can be a sign of an allergic reaction, which can be severe and life threatening.

Symptoms of an injection-related reaction are typically mild to moderate. They can include:

Because an injection-related reaction is most likely to happen with your first injection of Kesimpta, you will receive the first dose at your doctor’s office or clinic. This allows them to monitor for a reaction. They can then provide support and treatment, if needed.

If you have an injection-related reaction after giving yourself a dose of Kesimpta, call your doctor right away. If you feel you’re having a medical emergency, immediately call 911 or your local emergency number.

Injection site reactions

Injection site reactions were commonly reported in clinical trials of Kesimpta involving people with MS.

Injection site reactions occur near the area of the injection. These reactions are typically mild or moderate and go away within a few days. Symptoms of injection site reactions may include:

  • itching
  • pain
  • swelling
  • skin discoloration

If you experience these symptoms for longer than a few days or if they are severe or bothersome, talk with your doctor. They can recommend ways to relieve your symptoms and help prevent or lessen them in the future.

Low levels of immunoglobulins

Low levels of immunoglobulins occurred in clinical trials of Kesimpta. This side effect was common in trials. Immunoglobulins are a type of antibody protein produced by your immune system. They work to detect and fight bacteria and viruses in order to help prevent infections.

When levels of immunoglobulins are too low, your immune system is not able to fight off infections as effectively. This can lead to more frequent or more severe infections.

Symptoms of low immunoglobulins can include:

  • fever
  • skin rash
  • frequent infections

What you can do

Before starting Kesimpta, talk with your doctor about any current or chronic (long-term) infections you have. If you have a current infection, they may recommend that you wait until the infection is resolved before starting Kesimpta treatment.

If you develop an infection during Kesimpta treatment, tell your doctor. They will decide whether it’s safe to continue the medication.

Your doctor may also monitor your immunoglobulin levels with blood tests. This will help them determine your risk of infection and the safety of the medication for you.

Infections, including serious infections

Serious infections may occur during Kesimpta treatment. This is because Kesimpta reduces your MS symptoms by reducing your immune system’s activity.

Since your immune system activity is reduced during treatment, it’s not able to fight off infection as well. This increases your risk of both mild and serious infections. Mild infections were very common in clinical trials of Kesimpta, while serious infections were less common.

In Kesimpta’s trials, people experienced common mild infections, including:

There is also a risk of uncommon, more serious infections during Kesimpta treatment that may require hospitalization. An example of a very rare, serious infection is PML. This is a brain infection caused by the John Cunningham (JC) virus.

There were no cases of PML in clinical trials of Kesimpta. However, the infection was reported in clinical trials of the drug’s active ingredient (ofatumumab) in people with chronic lymphocytic leukemia. It’s also been reported in people receiving different antibody treatments and other MS treatments.

Most adults have the JC virus in their bodies. However, a healthy immune system typically prevents the virus from causing illness. Because Kesimpta reduces immune system activity, the JC virus could be reactivated and cause a severe brain infection.

Symptoms of PML include general weakness on one side of the body that progressively gets worse, difficulty speaking, memory problems, and personality changes.

What you can do

If you experience symptoms of a mild infection, such as the common cold, tell your doctor. They may want to monitor your symptoms and check that the infection goes away. If your immune system is not able to fight off a mild infection, your doctor will discuss with you the risks and benefits of continuing Kesimpta treatment.

If you have symptoms of a more severe infection, including those described for PML, talk with your doctor immediately. They may recommend that you stop Kesimpta treatment. If you feel that you’re having a medical emergency, immediately call 911 or your local emergency number.

Allergic reaction

As with most drugs, Kesimpta can cause an allergic reaction. A life threatening allergic reaction, called anaphylaxis, is possible with Kesimpta.

Symptoms of an allergic reaction can be mild or serious and can include:

  • skin rash
  • itching
  • flushing
  • swelling under your skin, typically in your eyelids, lips, hands, or feet
  • swelling of your mouth, tongue, or throat, which can make it hard to breathe
  • fast heart rate
  • dizziness
  • nausea

What you can do

For mild symptoms of an allergic reaction, call your doctor right away. They may recommend ways to ease your symptoms and determine whether you should continue Kesimpta treatment. However, if your symptoms are serious and you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Be sure to talk with your doctor about your health history before you start treatment with Kesimpta. This drug may not be the right treatment option for you if you have certain medical conditions or other factors that affect your health. These are known as drug-condition or drug-factor interactions.

The conditions and factors to consider include:

  • hepatitis B virus
  • active infection
  • any recent vaccinations
  • pregnancy
  • breastfeeding
  • previous allergic reaction to Kesimpta or any of its ingredients
  • alcohol consumption

Several common and mild side effects are possible with Kesimpta. They typically go away within a few days. Serious side effects may also be possible, though these are rare. Talk with your doctor about your medical history before starting Kesimpta treatment. They will discuss the risks and benefits of Kesimpta for your condition.

If you’d like to learn more about Kesimpta, talk with your doctor or pharmacist. They can help answer any questions you have about side effects from the drug.

Besides talking with your doctor, you can do some research on your own. These articles might help:

  • More information about Kesimpta: For details about other aspects of Kesimpta, refer to this article.
  • Cost: If you’d like to learn about Kesimpta and cost, refer to this article.
  • Dosage: For information about the dosage of Kesimpta, view this article.
  • A look at MS: For details about your condition, see our MS hub.

Disclaimer: Medical News Today has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.