Elrexfio (elranatamab-bcmm) is a prescription drug that’s used to treat multiple myeloma. Elrexfio can cause side effects that range from mild to serious. Examples include fatigue, diarrhea, and injection site reaction.

Specifically, Elrexfio is used in adults to treat multiple myeloma that is considered relapsed or refractory. (Relapsed means the cancer has come back after signs and symptoms lessened or couldn’t be found. Refractory means the cancer doesn’t respond to treatment or stops responding to it.) Typically, you would have tried four other therapies for multiple myeloma before starting Elrexfio.

Elrexfio is a biologic drug. The active ingredient in Elrexfio is elranatamab-bcmm. The drug comes as a liquid solution that a healthcare professional injects under your skin.

Keep reading to learn about the common, mild, and serious side effects that Elrexfio can cause. For a general overview of the drug, including details about its uses, see this article.

Elrexfio has boxed warnings. A boxed warning is the most serious warning from the Food and Drug Administration (FDA). For details, see the “Side effects explained” section below.

Some people may experience mild to serious side effects during their Elrexfio treatment. Examples of the drug’s commonly reported side effects include:

  • injection site reaction
  • fatigue (low energy)
  • diarrhea
  • muscle aches and pain
  • decreased appetite

The following sections include more side effects of Elrexfio. Each person’s experience with side effects may differ.

Mild side effects have been reported with Elrexfio. These include:

In most cases, these side effects should be temporary. And some may be managed easily. But if you have symptoms that are ongoing or bothersome, talk with your doctor or pharmacist. And do not stop Elrexfio treatment unless your doctor recommends it.

Elrexfio may cause mild side effects other than those listed above. See the drug’s prescribing information for details.

Serious side effects have been reported with Elrexfio. These include:

To learn more about CRS and neurologic toxicity, see the “Side effects explained” section below.

If you develop serious side effects during Elrexfio 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 call your local emergency number.

Note: After the FDA approves a drug, it tracks and reviews side effects of the medication. If you’d like to notify the FDA about a side effect you’ve had with Elrexfio, visit MedWatch.

Allergic reaction

For some people, Elrexfio can cause an allergic reaction. But this side effect wasn’t reported in the drug’s studies.

In general, symptoms of allergic reaction can be mild or serious. You can learn more about possible symptoms in this article.

What might help

If you have mild symptoms of an allergic reaction, such as a mild rash, call your doctor right away. They may suggest a treatment to manage your symptoms and can determine whether you should keep receiving Elrexfio.

If you have symptoms of a severe allergic reaction, such as swelling or difficulty breathing, call 911 right away. Or call your local emergency number. These symptoms could be life threatening and require immediate medical care.

Your doctor can confirm whether you’ve had a serious allergic reaction to Elrexfio. If they do, they may have you switch to a different treatment.

Learn more about some of the side effects Elrexfio may cause.

CRS

Elrexfio has a boxed warning for the risk of CRS. CRS involves the release of certain proteins into your blood. This leads to an overactive immune system. CRS can present with either mild or severe symptoms.

In studies of Elrexfio, both mild and severe symptoms have been reported. Usually, Elrexfio causes mild symptoms of CRS. But in rare cases, it can be severe or life threatening.

Mild symptoms of CRS include:

  • fever or chills
  • headache
  • dizziness

Severe symptoms of CRS can include:

What might help

Elrexfio is available for use through certified healthcare professionals and facilities under a restricted program. The program is ELREXFIO Risk Evaluation and Mitigation Strategy (REMS). It ensures that healthcare professionals are appropriately trained to give Elrexfio and manage its side effects. Additional information is available at the ELREXFIO REMS website or by telephone at 844-923-7845.

Following early doses of Elrexfio, you’ll likely need to remain in the facility where you received them. After your first dose, this may be at least 48 hours. After your second dose, this may be at least 24 hours. This allows your doctor to watch you closely for any serious side effects that could develop, such as CRS.

Your doctor may also prescribe medications to be given immediately prior to your Elrexfio injection. These medications can decrease your risk of CRS and include:

  • antihistamines, such as diphenhydramine (Benadryl)
  • fever reducers, such as acetaminophen (Tylenol) or ibuprofen (Motrin)
  • anti-inflammatories, such as prednisone (Rayos)

Watch for symptoms of CRS after receiving Elrexfio injections. If you develop CRS symptoms (noted above), talk with your doctor immediately. If the side effects seem life threatening or you think you’re having a medical emergency, immediately call 911. Or call your local emergency number.

Neurologic toxicity

Elrexfio has a boxed warning for risk of neurologic toxicity, including immune effector cell-associated neurotoxicity syndrome (ICANS). ICANS is a serious form of neurologic toxicity caused by an overactive immune system. Both neurologic toxicity and ICANS have been reported in studies of Elrexfio.

Neurologic toxicity can damage your nervous system, including your brain and spinal cord. These symptoms can be either mild or severe. In rare cases, neurologic toxicity can be life threatening.

Mild symptoms of neurologic toxicity include:

  • headache
  • numbness or tingling in the arms and legs

Severe symptoms of neurologic toxicity, such as ICANS, include:

  • confusion
  • difficulty speaking or writing
  • tiredness or sleepiness
  • muscle weakness
  • tremor
  • memory problems

What might help

Elrexfio is available for use through certified healthcare professionals and facilities under a restricted program. The program is ELREXFIO Risk Evaluation and Mitigation Strategy (REMS). It ensures that healthcare professionals are appropriately trained to give Elrexfio and manage its side effects. Additional information is available at the ELREXFIO REMS website or by telephone at 844-923-7845.

Following early doses of Elrexfio, you’ll likely need to remain in the facility where you received them. After your first dose, this may be at least 48 hours. After your second dose, this may be at least 24 hours. This allows your doctor to watch you closely for any serious side effects that could develop, such as neurologic toxicity and ICANS.

Avoid any activities that require alertness for at least 48 hours after receiving each of your first three doses of Elrexfio. These include driving and operating heavy machinery. If you have symptoms of neurologic toxicity, you should continue to avoid these activities until the symptoms resolve.

Watch for symptoms of neurologic toxicity, including ICANS, during Elrexfio treatment. If you develop symptoms of neurologic toxicity (noted above), talk with your doctor immediately. If the side effects seem life threatening or you think you’re having a medical emergency, immediately call 911. Or call your local emergency number.

Keeping track of side effects

During your Elrexfio treatment, consider taking notes on any side effects you’re having. You can then share this information with your doctor. This is especially helpful when you first start using a new drug or a combination of treatments.

Your side effect notes can include things such as:

  • what dose of the drug you were receiving when you had the side effect
  • how soon you had the side effect after starting that dose
  • what your symptoms were
  • how your symptoms affected your daily activities
  • what other medications you were taking
  • any other information you feel is important

Keeping notes and sharing them with your doctor will help them learn more about how Elrexfio affects you. They can then use this information to adjust your treatment plan if needed.

Below is important information you should consider before starting Elrexfio treatment.

Boxed warning: Risk of cytokine release syndrome (CRS) and neurologic toxicity

Elrexfio has boxed warnings. A boxed warning is the most serious warning from the FDA. For details, see the “Side effects explained” section above.

Other warnings

Elrexfio can sometimes cause harmful effects in people who have certain conditions. This is known as a drug-condition interaction. Other factors may also affect whether Elrexfio is a good treatment option for you.

Talk with your doctor about your health history before you begin Elrexfio treatment. Be sure to tell them if any of the following factors apply to you:

Disclaimer: Healthline 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.