Darzalex (daratumumab) is a prescription infusion that’s used to help treat multiple myeloma. Darzalex can cause side effects that range from mild to serious. Examples include atrial fibrillation (AFib) and respiratory infection.

Darzalex comes in two forms: Darzalex and Darzalex Faspro.

  • A healthcare professional gives Darzalex by intravenous (IV) infusion in a doctor’s office or clinic. An IV infusion is an injection into a vein that’s given over a period of time. Infusions of Darzalex take 3 to 7 hours.
  • Darzalex Faspro contains an extra ingredient called hyaluronidase-fihj. A healthcare professional gives this form of Darzalex by subcutaneous injection. This is an injection under your skin, and it takes about 3 to 5 minutes.

This article focuses mainly on the side effects of Darzalex. To read about the differences in side effects between the two forms of Darzalex, see the “FAQ about Darzalex’s side effects” section.

Keep reading to learn about the common, mild, and serious side effects that Darzalexcan cause. And for a detailed overview of this drug, check out this in-depth Darzalex article.

Some people may experience mild or serious side effects during their Darzalex treatment. Examples of Darzalex’s more commonly reported side effects include:

To learn more about some of these side effects, see the “Side effects explained” section.

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

To learn more about some of these side effects, see the “Side effects explained” section.

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

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

Serious side effects that have been reported with Darzalex include:

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

To learn more about some of these side effects, see the “Side effects explained” section.

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 Darzalex, visit MedWatch.

Allergic reaction

For some people, Darzalex can cause an allergic reaction. This side effect was reported in studies of Darzalex and Darzalex Faspro.

In general, symptoms of allergic reaction can be mild or serious.

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 continue treatment with Darzalex.

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 Darzalex, they may have you switch to a different treatment.

Here are the answers to some frequently asked questions about Darzalex’s side effects.

How long do Darzalex’s side effects last? Are there any long-term side effects?

Most mild side effects of Darzalex tend to lessen in a few days or a couple of weeks. If you have side effects that last longer or are troublesome, talk with your doctor.

Some serious side effects of Darzalex, such as infusion-related reactions, can decrease quickly with treatment. But others may last a long time, even with treatment. How long side effects last depends on how they respond to any treatments you have for them.

If you have questions or concerns about how long Darzalex side effects may last, talk with your doctor.

Do Darzalex and Darzalex Faspro have different side effects?

Darzalex is given by IV infusion, while Darzalex Faspro is given by subcutaneous injection. An IV infusion is an injection into a vein that’s given over a period of time. A subcutaneous injection is an injection given under your skin.

Darzalex and Darzalex Faspro can cause allergic reactions, including infusion reactions. These can happen during or shortly after the infusion or injection. Such allergic reactions are more common with Darzalex infusions than with Darzalex Faspro injections. But before you receive either form of Darzalex, you’ll be given medications to reduce your risk of having a reaction.

Darzalex Faspro can also cause mild skin reactions in the area where you have the injection. These can include redness or another change in skin color.

For more information about Darzalex Faspro’s side effects, you can see the drug’s prescribing information.

Can Darzalex cause heart problems?

Yes, Darzalex can sometimes cause cardiac (heart) problems when it’s used to treat multiple myeloma. In studies of Darzalex, a type of irregular heart rhythm called AFib was reported in some people.

Symptoms of AFib can include:

  • dizziness or lightheadedness
  • fainting
  • heart palpitations (feeling like your heart is racing, pounding, or skipping beats)
  • breathlessness, especially when exercising
  • chest pain or discomfort

If you have any of these symptoms, contact your doctor right away.

Learn more about some of the side effects that Darzalex may cause.

Infusion reaction

You’ll receive Darzalex as an IV infusion. An IV infusion is an injection into a vein that’s given over a period of time.

It’s possible to have a reaction to a Darzalex infusion. In fact, infusion reactions were one of the more common side effects reported in studies of Darzalex.

Certain infusion reactions may be caused by an allergic reaction to Darzalex. Typically, these reactions happen during or shortly after your Darzalex infusion.

Other infusion reactions may not occur for up to 3 days after your infusion.

Infusion reactions are usually mild or moderate, but they can be severe or life threatening. On rare occasions, they may even lead to death.

These reactions are most likely to happen with the first dose of Darzalex. You’re much less likely to have this side effect with subsequent doses.

Darzalex infusions can cause reactions such as:

What might help

Before each infusion of Darzalex, you’ll receive medications to reduce your risk of infusion reactions. You’ll usually be given a combination of:

You’ll also be given corticosteroids the day after your Darzalex infusion to reduce your risk of delayed reactions.

To lower your risk of infusion reactions, your first infusion will typically be given over about 7 hours. But after this, your infusions can usually be given over 3 to 5 hours.

A healthcare professional will monitor you closely during each infusion. If you have a mild or moderate reaction, they may pause your infusion to treat your symptoms. After your symptoms have gone away, they’ll restart the infusion at a slower rate. This is so you get the medication more slowly.

If you have a severe or life threatening reaction, your doctor may permanently stop your Darzalex treatment.

If you have a delayed reaction after leaving your doctor’s office or the infusion center, call your doctor right away. But if you have symptoms that feel life threatening or you think you’re having a medical emergency, call 911 right away.

For additional information about dosing for Darzalex, you can visit this Darzalex dosing guide.

Low blood cell counts

Like many cancer treatments, Darzalex commonly causes low blood cell counts. So, you may have low levels of white blood cells, red blood cells, or platelets while you have treatment with Darzalex.

A low level of neutrophils (a type of white blood cell) is called neutropenia. White blood cells help your body protect itself from germs that can cause infections. If you have neutropenia with Darzalex, you may have an increased risk of infections. Symptoms of infections can include:

A low level of red blood cells is called anemia. Red blood cells carry oxygen throughout your body. If you have anemia with Darzalex, you may have symptoms such as:

A low level of platelets is called thrombocytopenia. Platelets help your blood clot after an injury. If you have thrombocytopenia with Darzalex, you may have symptoms such as:

  • bruising easily
  • bleeding, such as nosebleeds or bleeding gums
  • taking longer than usual to stop bleeding

What might help

Your doctor will check your blood cells frequently while you have Darzalex. During or after the treatment, tell your doctor right away if you have symptoms of low blood cell counts.

If you have low blood cell counts, your doctor may delay your next Darzalex infusion until your blood cell levels recover.

Respiratory infection

You may get respiratory infections while you’re having treatment with Darzalex. In fact, upper respiratory infections, such as colds, were commonly reported in studies of the drug.

Respiratory infections are typically mild, but they can sometimes become more serious and affect your lungs. Serious infections, such as the flu, bronchitis, and pneumonia, have been reported in people taking Darzalex.

Symptoms of serious respiratory infections may include:

  • cough
  • coughing up blood or phlegm
  • shortness of breath
  • chest pain
  • fever
  • shivering
  • extreme lack of energy

What might help

You can help protect yourself from respiratory infections while you’re having Darzalex treatment by:

Before you start receiving Darzalex, talk with your doctor about getting vaccines, such as the flu shot, COVID-19 vaccine, or pneumonia vaccine.

If you get a mild respiratory infection, such as a cold, during your treatment, talk with your doctor or pharmacist. If your symptoms are troublesome, they can recommend over-the-counter treatments that are suitable for you.

But if the infection doesn’t get better after a few days or your symptoms start to get worse, contact your doctor. You may need medication to treat the infection and stop it from getting worse.

If you have symptoms of a serious respiratory infection, contact your doctor right away. You’ll need medication to treat the infection.

Peripheral sensory neuropathy

Darzalex can sometimes cause a side effect called peripheral sensory neuropathy. This is nerve damage that causes tingling or burning sensations, numbness, or pain in your hands or feet.

In studies of Darzalex, peripheral sensory neuropathy was one of the more commonly reported side effects.

What might help

If you have symptoms of peripheral sensory neuropathy while you’re having Darzalex treatment, talk with your doctor. They can suggest ways to help manage this side effect.

For example, if you have troublesome pain in your hands or feet, your doctor may prescribe medication to help with this. They may suggest a numbing cream or patch to put directly on the area where you’re having pain. Or they may prescribe certain antidepressants or seizure medications that are also used for nerve pain.

Other treatments that may be helpful for this nerve problem include physical therapy, acupuncture, and electrical nerve stimulation. Your doctor can tell you more about these treatments.

Here are some other tips to help manage this side effect:

  • Hot and cold temperatures can sometimes make neuropathy worse. If this is the case for you, avoid taking hot baths or showers. You may also want to keep your hands and feet covered and warm in cold temperatures.
  • If you have numbness, this can lead to injuries. Take care of your hands and feet, and check them often to make sure you don’t have any sore or damaged areas.
  • If the neuropathy is in your feet, always wear shoes that protect your whole foot, even when you’re at home. And make sure that your shoes aren’t too tight.
  • If the neuropathy is in your hands, take extra care when using sharp objects, such as knives or scissors.
Keeping track of side effects

During your Darzalex treatment, consider keeping notes about any side effects you’re having. Then, you can 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 after starting that dose you had the side effect
  • your specific symptoms from the side effect
  • how it affected your daily activities
  • any other medications you were also taking
  • any other information you feel is important

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

Darzalex 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 Darzalex is a good treatment option for you.

Talk with your doctor about your health history before you receive Darzalex. 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.