If you have multiple myeloma, your doctor might suggest Blenrep as a treatment option for you. Blenrep is a prescription medication that’s used in adults to treat this type of cancer in certain situations. Learning more about the possible side effects of Blenrep can help you and your doctor better personalize your treatment plan.

The active ingredient in Blenrep is belantamab mafodotin-blmf. An active ingredient is what makes a drug work. Blenrep is a biologic drug, which means it’s made from living cells.

This drug is given by a healthcare professional as an intravenous (IV) infusion (an injection given slowly into a vein) at a doctor’s office or clinic.

For more information about Blenrep, including details about its use, see this in-depth article.

Like other drugs, Blenrep can cause mild to serious side effects (also known as adverse effects). Keep reading to learn more.

You may experience mild or serious side effects during treatment with Blenrep.

Some examples of Blenrep’s commonly reported side effects include:

* To learn more about this side effect, see the “Side effects explained” section below.

Keep reading to learn about Blenrep’s other possible mild and serious side effects.

Blenrep treatment can cause some mild side effects.

Examples of mild side effects that have been reported with Blenrep include:

* To learn more about this side effect, see the “Side effects explained” section below.

In most cases, these side effects should be short term. And some may be easily managed. But if you have any symptoms that are ongoing or bother you, talk with your doctor or pharmacist. They can discuss your concerns and any changes to your treatment plan.

Blenrep may cause mild side effects other than the ones listed above. See the Blenrep prescribing information for details.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks side effects of the medication. If you’d like to notify the FDA about a side effect you’ve had with Blenrep, visit MedWatch.

In some people, Blenrep may cause serious side effects, a few being more common than others. How severe a side effect is varies. It can depend on factors such as a person’s overall health and other medications they may be taking.

Serious side effects include:

* Blenrep has a boxed warning for this side effect. This is the most serious warning from the Food and Drug Administration (FDA). To learn more, see the “Side effects explained” section below.
† To learn more about this side effect, see the “Side effects explained” section below.
‡ An allergic reaction is possible after using Blenrep. But it’s not clear whether this side effect occurred in studies.

If you develop serious side effects while taking Blenrep, 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.

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

Risk of serious eye problems

Blenrep has a boxed warning for risk of serious eye problems (also known as ocular side effects). A boxed warning is the most serious warning from the Food and Drug Administration (FDA). It alerts doctors and patients about drug effects that may be dangerous.

Blenrep may cause changes to the cornea, which is the outer layer in the front part of the eye. These changes may result in corneal ulcers (sores), dryness, blurred vision, and, in serious cases, loss of vision.

What might help

Before you begin treatment with Blenrep, your doctor will ask you to visit an eye doctor to check your eyes. This is part of a safety program called the Blenrep Risk Evaluation and Mitigation Strategy (REMS). For more information about this program, see the section just below.

As long as you’re receiving Blenrep, you’ll have your eyes checked before each dose of the drug.

If you have any eye-related side effects during Blenrep treatment, contact your doctor right away. They’ll ask an eye specialist to examine your eyes. Depending on the results, your doctor may lower your dose or stop treatment if needed.

Blenrep REMS Program

The Blenrep REMS Program is a safety program designed to manage eye-related risks associated with Blenrep. Your doctor must be specially trained, and the clinic where you receive Blenrep must be certified to give the drug. You will also have to enroll in the Blenrep REMS program to receive this drug.

If you have questions about the Blenrep REMS Program, talk with your doctor.

Nausea

Blenrep may cause nausea. In studies of the drug, this was a commonly reported side effect.

For most people, nausea eases with time. But in some cases, nausea may be more serious or long lasting.

What might help

A healthcare professional will give you Blenrep as an intravenous (IV) infusion (an injection given slowly into a vein) at a doctor’s office or clinic. They’ll monitor you during and after you receive your dose.

If you experience severe nausea during your infusion, the healthcare professional may pause or slow your treatment. For most people, the nausea is not serious.

For mild nausea, try eating smaller, more frequent meals and avoiding greasy foods. Drinking ginger tea or peppermint team may also ease this side effect.

Your doctor can offer other suggestions to help manage this side effect, including medications you may take.

If you have severe nausea or vomiting with dizziness during Blenrep treatment, talk with your doctor. They can discuss your treatment plan and whether Blenrep is suitable for you.

Fatigue

In studies of Blenrep, fatigue (low energy) was one of the more commonly reported side effects. Fatigue eases over time for most people during Blenrep treatment. But in some cases, it can last longer and be more serious.

Fatigue may also be caused by multiple myeloma, the condition you’re using this drug to treat, or other medications you may be taking.

What might help

While you’re receiving Blenrep, your doctor will check your blood cell count. Low levels of blood cells can cause fatigue.

To help ease this side effect, try getting adequate rest, eating a healthy diet, and not overexerting yourself. Your doctor can offer other suggestions to manage fatigue while you’re using Blenrep.

If you have serious fatigue that is affecting your daily life, talk with your doctor. They may recommend other treatment options that are more suitable for you.

Fever

Blenrep can often cause fever, which is usually considered a mild side effect. But in some cases, fever may be a sign of an infection, which can be serious. Blenrep can cause severe infections such as pneumonia or sepsis (serious blood infection).

What might help

If you have a fever while receiving Blenrep treatment, contact your doctor right away. They may order blood tests to check for an infection. If you have an infection, they’ll likely have you temporarily stop receiving Blenrep and treat the infection.

If you have a mild fever, your doctor may suggest taking an over-the-counter (OTC) fever reducer to ease this side effect. An example is Tylenol (acetaminophen). Before taking any OTC products, always talk with your doctor. They can recommend a fever reducer that is safe for you.

Low platelet levels

Treatment with Blenrep may cause low platelet counts. (Platelets are a type of blood cell that helps your blood to clot.) This was a common side effect in studies of the drug.

This condition may increase your risk of severe bleeding problems, including hemorrhage (serious internal bleeding).

Symptoms of low platelet levels include:

What might help

Your doctor will monitor your blood cell levels while you’re receiving Blenrep treatment. If your platelet counts are low, your doctor may:

  • lower your dose
  • skip or delay your treatment to let your platelet levels increase
  • stop treatment permanently, in rare cases of a serious reaction

If you have symptoms such as bruising easily or bleeding, contact your doctor. They can order blood tests and, based on your platelet levels, discuss options for your treatment plan.

Allergic reaction

Like most drugs, Blenrep can cause an allergic reaction in some people. But it’s not clear whether this side effect occurred in studies.

Symptoms can be mild to serious and can include:

  • skin rash
  • itchiness
  • flushing (temporary warmth, redness, or deepening of skin color)
  • swelling under your skin, usually in your eyelids, lips, hands, or feet
  • swelling of your mouth, tongue, or throat, which can make it hard to breathe

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. Examples include:

  • an over-the-counter antihistamine you take by mouth, such as Benadryl (diphenhydramine)
  • a product you apply to your skin, such as hydrocortisone cream

If your doctor confirms you’ve had a mild allergic reaction to Blenrep, they’ll decide if you should continue using it.

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

If your doctor confirms you’ve had a serious allergic reaction to Blenrep, they may have you switch to a different treatment.

Keeping track of side effects

During your Blenrep 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 taking new drugs or using a combination of treatments.

Your side effect notes can include things such as:

  • what dose of the drug you were taking when you had the side effect
  • how soon you had the side effect after starting that dose
  • what your symptoms were
  • how it 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 Blenrep affects you. They can then use this information to adjust your treatment plan if needed.

Below are answers to some frequently asked questions about Blenrep’s side effects.

Can treatment with Blenrep cause liver damage?

It’s possible. Blenrep can increase liver enzyme levels. This can cause liver damage if it’s severe. But it’s currently not known whether you have higher risk of liver damage from Blenrep if you have liver disease.

Tell your doctor if you have a history of liver disease or symptoms of liver damage, such as:

  • jaundice (yellowing of the skin or whites of the eyes)
  • fatigue (low energy)
  • belly pain

Your doctor will order blood tests to check your liver function while you’re receiving Blenrep. If your liver enzymes are high, they may pause Blenrep treatment and do more testing. In serious cases, they may stop treatment permanently.

For more information about liver damage and Blenrep, talk with your doctor.

Does Blenrep cause shortness of breath?

It’s possible. Although shortness of breath was not reported in studies of Blenrep, the drug may cause infusion-related reactions. These are side effects that can happen during treatment or within a short time after. Shortness of breath is a possible serious reaction of infusions. Other serious infusion-related side effects include headache, chest pain, changes in blood pressure, and seizures.

The healthcare professional giving your infusion will monitor you while you receive the drug. If you develop infusion-related side effects, they’ll likely pause the infusion and treat your reaction. They may resume the infusion at a slower rate while monitoring you. If you have another reaction, they may stop Blenrep treatment permanently.

Before you start using Blenrep, your doctor will discuss possible serious side effects of the drug. This includes what you may experience with an infusion.

Can I drive after receiving treatment with Blenrep?

It depends on your reaction to treatment. Blenrep can cause eye problems, including blurred vision. Before you start using Blenrep and before you receive each dose, your doctor will have an eye doctor check your vision. They’ll also send you to an eye doctor if there are any changes or problems with your vision.

Due to potential eye-related side effects, you need to use caution when driving after treatment with Blenrep. It may be helpful to plan for someone to drive you home after the first few infusions until you know how you react to the drug.

For more information about this side effect and whether it’s safe for you to drive after receiving treatment, talk with your doctor.

Blenrep comes with several warnings. Discussing these warnings with your doctor can help you decide whether this drug is a good treatment option for you.

Boxed warning: Risk of serious eye problems

Blenrep has a boxed warning for the risk of serious eye problems. A boxed warning is the most serious warning from the Food and Drug Administration (FDA).

Blenrep may cause changes to the cornea, which is the outer layer in the front part of the eye. If you already have eye problems, let your doctor know. Treatment with Blenrep may increase your risk of eye problems.

Due to this risk, Blenrep is only available through a safety program called the Blenrep Risk Evaluation and Mitigation Strategy (REMS).

To learn more, see the “Side effects explained” section above.

Other warnings

Blenrep may not be right for you if you have certain medical conditions or other factors that affect your health. Talk with your doctor about your health history before starting Blenrep. The list below includes factors to consider.

Bleeding problems. Blenrep may cause low platelet levels. For people who have bleeding disorders, the drug may increase the risk of severe bleeding problems. This includes hemorrhage (serious internal bleeding). If you have a history of bleeding problems, tell your doctor. They’ll discuss whether Blenrep is safe for you.

Allergic reaction. If you’ve had an allergic reaction to Blenrep or any of its ingredients, your doctor will likely not prescribe Blenrep. Ask them what other medications are better options for you.

Alcohol use and Blenrep

It is not known if Blenrep interacts with alcohol. If you plan to drink, ask your doctor how much is safe for you to consume during Blenrep treatment.

Pregnancy and breastfeeding while taking Blenrep

Blenrep may cause harm to a developing fetus, so it is not safe to use during pregnancy. If you can become pregnant, your doctor will give you a pregnancy test before you start Blenrep treatment.

Females* should use an effective form of birth control during treatment and for 4 months after their last dose of the drug. Males* with partners who can become pregnant should also use birth control during treatment and for 6 months afterward.

If you become pregnant while using Blenrep, tell your doctor right away. Also let your doctor know if you’re planning a pregnancy. They’ll discuss other treatment options with you.

It’s not known if Blenrep passes into breast milk. Because of possible harm to a breastfed child, you should not breastfeed during Blenrep treatment. And you should wait 3 months after stopping treatment before breastfeeding.

If you’re currently breastfeeding, ask your doctor about safer treatment options for your condition.

* In this article, we use the terms “male” and “female” to refer to someone’s sex assigned at birth. For information about the difference between sex and gender, see this article.

Blenrep is used in adults to treat multiple myeloma in certain situations.

Like many drugs, Blenrep can cause mild and serious side effects. To help you decide whether Blenrep is a good treatment option for you, ask your doctor questions about the drug, including its possible side effects.

Here are a few questions you might want to ask:

  • What can I do to manage side effects of Blenrep?
  • Can other medications I take worsen my risk of side effects of this drug?
  • Will my side effects lessen as I continue Blenrep treatment?

Q:

How can I lower my risk of an infection during Blenrep treatment?

Anonymous

A:

Multiple myeloma is a type of cancer that affects your white blood cell levels. White blood cells help fight infections. So lower levels of these blood cells can make it harder for your immune system to work against an infection. Also, in studies of Blenrep, the drug was found to increase the risk of infections.

While you’re using Blenrep, your doctor will check your blood cell counts. If you have low white blood cell levels, your doctor will discuss whether you need treatment to improve these levels. Or they may recommend decreasing your dose of Blenrep, or temporarily or permanently stopping treatment with this drug.

A few things you can do to lower the risk of infection include regular handwashing, avoiding crowds, and not being in close contact with people who are sick.

If you have a fever or other symptoms of an infection, tell your doctor right away. They’ll likely order tests to check for infection. If you have an infection, they’ll treat it.

For more information on the risk of infection with Blenrep and other ways to lower this risk, talk with your doctor.

The Healthline Pharmacist TeamAnswers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.

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.