7 Darzalex Side Effects and How to Manage Them

GoodRx Health

Darzalex (daratumumab) is a monoclonal antibody medication that's used to treat multiple myeloma in adults. In fact, Darzalex was the first monoclonal antibody to be FDA approved for this specific form of blood cancer.

This medication is given as an intravenous (IV) infusion through your vein. But it's also available as a subcutaneous (under the skin) injection in a different formulation, called Darzalex Faspro (daratumumab / hyaluronidase).

Both forms of daratumumab affect myeloma cancer cells, but they can also affect healthy cells. This can lead to side effects. In some cases, side effects can become serious and warrant immediate medical attention.

Darzalex side effects at a glance

Your oncologist is the best resource for learning about Darzalex side effects. But here's a list you can use to get the conversation started with them.

Common Darzalex side effects include:

• Infusion-related reactions (Darzlex specifically)

• Injection-related reactions (Darzalex Faspro specifically)

• Low white blood cell counts

• Low red blood cell counts

• Low platelets

• Tiredness

• Nausea

• Diarrhea

• Constipation

• Nerve pain

• Back pain

• Cough

• Fever

• Upper respiratory tract infections

Rare but serious side effects of Darzalex include:

• Severe infusion-related reactions

• Serious infection

• Heart problems (Darzalex Faspro specifically)

Here, we'll dive deeper into seven notable Darzalex side effects to know about. We'll also walk through how to manage them and what to expect if you receive Darzalex versus Darzalex Faspro.

1. Infusion reactions

Darzalex commonly causes infusion-related reactions. A little over one-third of people who receive Darzalex experience some degree of a reaction. Infusion reactions are more likely during the first infusion and are less likely to happen with infusions after that.

Infusion-related reactions are similar to an allergic reaction to a medication. Symptoms of an infusion reaction to be aware of include:

• Fever

• Cough

• Chills

• Stuffy nose

• Trouble breathing

• Nausea

• Changes in blood pressure

Let your care team know right away if you're having symptoms of an infusion-related reaction. But if you experience a fever, trouble breathing, or changes in blood pressure, you should seek medical attention right away. Symptoms like these are a sign of a more severe reaction.

Managing infusion reactions

To lower your risk of infusion reactions, your oncologist will likely give you acetaminophen (Tylenol), diphenhydramine (Benadryl), and a corticosteroid as "premedications" before each infusion. Montelukast (Singulair) may also be recommended to lower your risk further.

Your oncologist may also want you to take a corticosteroid, such as methylprednisolone or dexamethasone, for a couple days after each infusion to prevent a delayed infusion reaction. A delayed infusion reaction is one that can happen up to 2 days after receiving Darzalex.

To lower your risk of an infusion-related reaction even more, your first few Darzalex infusions will be given at a slower rate. If you tolerate your first few Darzalex infusions well, you can receive future infusions at a faster rate.

If you experience a mild or moderate infusion-related reaction, your oncologist will likely restart your Darzalex infusions at a slower rate moving forward. If you experience a severe infusion-related reaction, you may need to stop Darzalex permanently.

2. Low blood cell counts

Darzalex can cause low blood cell counts, including low white blood cells and low platelets. White blood cells are an important part of the immune system and play a key role in fighting off infections. Platelets are important for blood clotting and preventing excessive or accidental bleeding.

When white blood cells are low, you have a higher risk of developing an infection. Your oncologist should regularly monitor your blood cell counts while you're receiving Darzalex because of this. If your white blood cell counts become too low, they may recommend taking antibiotics or antiviral medications to prevent certain viral or bacterial infections.

When platelets are low, you may not be able to stop bleeding. Signs of low platelets include nosebleeds and bleeding and bruising more easily. If you notice bleeding that's hard to stop or see blood in your urine or stool, contact your oncologist right away.

3. Infection

Mild upper respiratory tract infections, such as colds, are common with Darzalex. But some infections can become serious, such as the flu or pneumonia.

To help protect yourself from getting an infection, do your best to wash your hands frequently, avoid crowded places, and stay away from other people who are sick. It's also helpful to wash raw fruit and vegetables well before eating them. And consider getting flu, pneumonia, and COVID-19 vaccines before you start Darzalex.

Let your oncologist know right away if you have a fever of 100.4℉ or higher. This may be a sign of an infection. Milder infections can usually be treated with over-the-counter (OTC) medications. But severe infections will likely require prescription medications - as well as a pause in your cancer treatment - to treat the infection.

4. Diarrhea or constipation

Darzalex can affect your bowel movements. It may cause diarrhea or constipation, depending on the person.

If you have diarrhea while you're taking Darzalex, try to stay well hydrated by drinking plenty of fluids throughout the day. Avoid sugary drinks, though, because they can make diarrhea worse. You can also try an OTC diarrhea medication, such as loperamide (Imodium A-D), if needed.

For constipation, try to eat a high fiber diet with plenty of fruits and vegetables. Drink lots of fluids, too. Physical exercise can also help get things moving. OTC medications for constipation, such as stool softeners like docusate (Colace) and laxatives like senna (Senokot, Ex-Lax), can help ease constipation when needed.

Good to know: OTC diarrhea and constipation products should only be used short term. Based on your medical history, your oncologist can tell you how long and how often you can take them safely.

5. Nerve pain and nerve weakness

Darzalex can sometimes cause nerve pain, also known as peripheral neuropathy. It's caused by nerve damage and can lead to symptoms such as tingling sensations and pain or numbness in your hands or feet.

One way to help manage nerve pain from Darzalex is by wearing shoes that aren't too tight and protect your feet well. Avoid overly hot showers or cold temperatures - these temperature extremes can make nerve pain worse. Also, keep your hands and feet covered in cold temperatures.

If your nerve pain becomes excessive, speak with your oncologist. They may be able to suggest ways to manage nerve pain with medications such as gabapentin (Neurontin) or duloxetine (Cymbalta). Alternative therapies, such as physical therapy and acupuncture, may also help.

6. Fatigue

Tiredness, or feeling like you have no energy, is common with Darzalex. Nearly 40% of people who received Darzalex infusions in clinical trials reported some level of fatigue.

To help manage fatigue from Darzalex, rest and take short naps when you need them. You can also try gentle exercises, such as walking, to boost your energy levels. If you feel very tired after your Darzalex treatments, it's a good idea to have a caregiver or family member assist with driving, cooking, and other attention-oriented tasks.

Let your oncologist know if you feel too tired or weak to complete your normal daily activities. They may be able to suggest other ways to help cope with fatigue, such as treating low blood cell counts or pain that may be contributing to fatigue.

7. Back pain

Back pain is another side effect of Darzalex that can be bothersome. Back pain is thought to happen because of the release of inflammatory proteins in the body as a reaction to Darzalex.

About a quarter of people who received Darzalex reported having back pain in initial studies. Speak with your oncologist if you experience back pain with Darzalex. Several medications can help relieve symptoms of back pain. Your oncologist can recommend one that may be appropriate for you.

Natural remedies are another option. Some options to manage back pain include getting a massage, applying heat or ice to the area, or seeing a chiropractor for spinal manipulation.

Do Darzalex and Darzalex Faspro cause the same side effects?

Darzalex and Darzalex Faspro both contain daratumumab. But they have a few differences. The main distinction is that Darzalex Faspro contains an enzyme (protein) called hyaluronidase. This allows daratumumab to be given as an injection under the skin rather than as an IV infusion.

Darzalex Faspro has similar side effects as traditional Darzalex infusions. However, Darzalex Faspro isn't an infusion. So it doesn't cause infusion-related reactions. Rather, it can cause injection-related reactions. Symptoms of an injection-related reaction include redness and swelling at the injection site. Injection reactions are also more common with your first Darzalex Faspro injection, but they should get better over time.

What's more, in addition to multiple myeloma, Darzalex Faspro is approved to treat light chain amyloidosis. Some people who received Darzalex Faspro for amyloidosis have experienced serious heart problems, such as heart failure. If you have a history of heart problems, you may be at a higher risk of this side effect if you receive Darzalex Faspro for amyloidosis.

Traditional Darzalex isn't approved for amyloidosis. So we don't know if there is a higher risk of heart problems with it.

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