7 Darzalex Side Effects and How to Manage Them

Darzalex side effects at a glance

Your oncology team is the best resource for learning about Darzalex side effects. But here are two lists you can use to get the conversation started with them.

Common Darzalex side effects include:

• Upper respiratory tract infections

• Infusion- or injection-related reactions

• Low white blood cell counts

• Low red blood cell counts

• Low platelets

• Fatigue

• Weakness

• Nausea

• Diarrhea

• Constipation

• Nerve pain

• Back pain

• Cough

• Fever

• Swelling in feet and/or hands

Rare side effects of Darzalex include:

• Severe infusion-related reactions

• Serious infections

• Heart problems (with Darzalex Faspro only)

Here, we'll dive deeper into seven notable Darzalex side effects. 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. This side effect is more likely during the first infusion and becomes less likely with the following infusions.

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

• Fever

• Cough

• Chills

• Stuffy nose

• Trouble breathing

• Nausea

• Changes in blood pressure

Your care team should monitor you during and after your Darzalex infusions to keep an eye out for this side effect. But let them know right away if you’re having any of the above symptoms.

While rare, you may develop symptoms of an infusion-related reaction up to 48 hours after a treatment — known as a delayed infusion reaction. If you experience a fever, trouble breathing, or changes in your heart rate in the days after an infusion, seek emergency medical attention right away.

2. Low blood cell counts

Darzalex can lower the number of red blood cells, white blood cells, or platelets in your body. Your oncologist should regularly monitor your blood cell counts while you're receiving Darzalex because of this. 

Red blood cells carry oxygen in the blood. Low levels of red blood cells can lead to anemia, which can make you feel weak or more tired than usual.

White blood cells play a key role in fighting off infections. So low levels of white blood cells increase your risk of developing infections (discussed below). If your white blood cell counts become too low, your oncologist may recommend taking antibiotics or antiviral medications to help prevent certain bacterial or viral infections.

Platelets are important for blood clotting. When platelets are low, you’re at a higher risk of unwanted 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. Infections

As mentioned, Darzalex can increase your risk of infections. Common examples include mild upper respiratory tract infections, such as the common cold. But more serious infections, such as the flu or pneumonia, are also possible.

To help protect yourself from getting an infection:

• Wash your hands (or use hand sanitizer) often.

• Try to avoid crowded places.

• Stay away from other people who are sick.

• Wash raw fruit and vegetables well before eating them.

Getting flu, pneumonia, and COVID-19 vaccines before you start Darzalex can also help protect you against these infections.

Let your oncologist know right away if you have a fever of 100.4℉ or higher at any point during Darzalex treatment. 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 treatment with prescription medication, as well as a pause in your cancer treatment.

4. Diarrhea or constipation

Darzalex can affect your bowel movements, causing diarrhea or constipation.

If you have diarrhea while you’re receiving 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, drink lots of fluids and try to eat a high-fiber diet full of fruits and vegetables. 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 also help ease constipation when needed.

Good to know: In general, you should only take OTC diarrhea and constipation products short term. Long-term use requires approval from your oncology team. Be sure to let them know about any stool changes that don’t improve or get worse while you’re receiving Darzalex.

5. Nerve pain

Darzalex can sometimes cause nerve pain, also known as peripheral neuropathy. The pain is 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 and exposure to cold temperatures, as extreme temperatures can make nerve pain worse. Also, keep your hands and feet covered in the cold.

If your nerve pain becomes excessive, speak with your oncologist. They may prescribe a medication such as gabapentin (Neurontin) or duloxetine (Cymbalta) to help manage it. Alternative therapies, such as physical therapy and acupuncture, may also help.

6. Fatigue

Feeling weak or low on energy is common with Darzalex.

To help manage fatigue from Darzalex, rest and take short naps when needed. You can also try gentle exercises, such as walking, to help 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 can check for low blood cell counts or pain that may be contributing to fatigue and suggest a treatment if warranted.

7. Back pain

Back pain is another potentially bothersome Darzalex side effect. There are several possible causes:

• It’s believed that your body releases inflammatory proteins in the body, which can contribute to back pain, as a reaction to Darzalex.

• Back pain may be a symptom of an infection related to low white blood cell levels.

• Infusion-related reactions can also contribute to back pain.

• Back pain may also be caused by multiple myeloma itself.

Several medications can help relieve symptoms of back pain. Your oncologist can recommend one that is appropriate for you. You can also try nonmedication remedies. Some options include getting a massage, applying heat or ice to the area, and 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 to traditional Darzalex infusions. But it can cause injection-related reactions instead of infusion-related reactions. Symptoms of an injection-related reaction include redness and swelling at the injection site. Injection reactions are more common with your first Darzalex Faspro injection, but they should get better over time.

Unlike Darzalex, Darzalex Faspro is also approved to treat a condition called light chain amyloidosis. Some people who have 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.

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Written by:

Sonja Jacobsen, PharmD, BCPS, BCOP

Sonja Jacobsen, PharmD, BCPS, BCOP,  is a clinical oncology pharmacy specialist currently practicing in Seattle. She has been practicing as a pharmacist since 2015 and is licensed to practice in Washington state and North Carolina.

Edited by:

Stacia Woodcock, PharmD

Stacia Woodcock, PharmD, is a pharmacy editor for GoodRx. She earned her Doctor of Pharmacy degree from the University of Kentucky and is licensed in New York and Massachusetts.

Reviewed by:

Joshua Murdock, PharmD, BCBBS

Joshua Murdock, PharmD, BCBBS, is a licensed pharmacist in Arizona, Colorado, and Rhode Island. He has worked in the pharmacy industry for more than 10 years and currently serves as a pharmacy editor for GoodRx.

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