Enhertu (fam-trastuzumab deruxtecan-nxki) is a brand-name intravenous (IV) infusion that’s prescribed for certain types of cancer in adults. As with other drugs, Enhertu can cause side effects such as hair loss and low white blood cell levels.

Specifically, Enhertu treats the following HER2-positive cancers (cancers with a high level of a protein called HER2) in certain situations:

Enhertu is an antibody-drug conjugate. This means it contains two active ingredients: fam-trastuzumab, which is an HER2 antibody, and deruxtecan-nxki, which is a topoisomerase I inhibitor (a type of chemotherapy). The drug is not available in a generic version.

Read on to learn about potential common, mild, and serious side effects of Enhertu. For a general overview of the drug, including details about its uses, see this article.

* For this use, Enhertu received accelerated approval from the Food and Drug Administration (FDA). This means its approval is based on information from early trials. The FDA will decide about full approval after more trials are completed.

Enhertu can cause certain side effects, some of which are more common than others. These side effects may be temporary, lasting a few days to weeks. If the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

These are just a few of the more common side effects reported by people who took Enhertu in clinical trials:

* For more information about this side effect, see “Side effect specifics” below.

Mild side effects can occur with Enhertu. This list doesn’t include all possible mild side effects of the drug. For more details, you can refer to Enhertu’s prescribing information.

Mild side effects that have been reported with Enhertu include:

These side effects may be temporary, lasting a few days to weeks. If the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks side effects of the medication. If you develop a side effect with Enhertu and want to tell the FDA about it, visit MedWatch.

* For more information about this side effect, see “Side effect specifics” below.

Enhertu may cause serious side effects. The list below may not include all possible serious side effects of the drug. For more details, you can refer to Enhertu’s prescribing information.

If you develop serious side effects with Enhertu, 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.

Serious side effects that have been reported with Enhertu and their symptoms include:

* To learn more, see the “Side effect specifics” section below.
† Enhertu has a boxed warning for this side effect. A boxed warning is the most serious warning from the Food and Drug Administration (FDA).
‡ For more information, see “Pregnancy and breastfeeding while receiving Enhertu” in the “Precautions for Enhertu” section below.
§ An allergic reaction is possible after receiving Enhertu. However, it’s not clear whether this side effect occurred in clinical trials.

Read below to learn more about some of the side effects Enhertu may cause. To find out how often side effects occurred in clinical trials, see the prescribing information for Enhertu.

Hair loss

People who received Enhertu in clinical trials commonly reported hair loss. Several other medications that treat breast cancer and non-small cell lung cancer also commonly cause hair loss. (Enhertu also treats certain forms of stomach and esophageal cancer.)

Hair loss may include thinning hair, losing hair in patches, or losing all your hair.

In addition to the loss of hair on your head, it’s possible that Enhertu treatment can cause hair loss on other body parts. These can include your arms and legs. The drug may also affect eyebrows and eyelashes.

Hair loss from Enhertu is usually temporary. Once you have finished Enhertu treatment, your hair should start to grow back.

What you can do

If you’re concerned about hair loss during your Enhertu treatment, talk with your doctor. They may be able to suggest ways to help manage this side effect.

Digestive side effects

Constipation, diarrhea, and indigestion were common digestive side effects of Enhertu in clinical trials.

Symptoms of constipation include lumpy or hard stools and difficulty passing stools. Diarrhea may cause watery stools, stomach pain, bloating, and cramps. Symptoms of indigestion can include pain or burning in the digestive system and feeling too full after eating.

What you can do

If you’re concerned about digestive problems during your Enhertu treatment, talk with your doctor. They can suggest ways to ease your symptoms without medication. These can include drinking plenty of water to help relieve constipation and diarrhea. Also, eating slowly helps prevent indigestion.

Your doctor may also recommend over-the-counter or prescription medication. If your digestive side effects are severe, your doctor may switch you to a drug other than Enhertu.

Decreased heart function

During Enhertu treatment, the left side of the heart may not function correctly. This can cause blood to become backed up in the lungs, which sometimes leads to heart failure. Decreased heart function was a rare side effect in people who received Enhertu in clinical trials.

To see whether the left side of your heart (left ventricle) is pumping properly, your doctor will look at your left ventricular ejection fraction (LVEF) periodically while you’re receiving Enhertu.Ejection fraction refers to how much blood your heart pumps with each contraction.

It’s possible for decreased LVEF to not cause noticeable symptoms. Or you may have symptoms such as cough, trouble breathing, and rapid weight gain. Other possible symptoms can include lightheadedness or dizziness, tiredness, and fluid buildup that’s mostly in the legs or ankles.

What you can do

While you receive Enhertu, your doctor will check your LVEF from time to time. If your LVEF decreases, your doctor will usually have you switch to a different drug.

Severe lung problems

Enhertu has a boxed warning about the risk of severe lung problems. A boxed warning is the most serious warning from the Food and Drug Administration (FDA).

Enhertu may increase the risk of serious lung conditions, including pneumonitis and interstitial lung disease (ILD). They can cause scarring and inflammation in your lungs. In severe cases, the conditions may lead to a hospital stay and, sometimes, death.

Note: Enhertu is approved* to treat non-small cell lung cancer, and this condition can cause symptoms of severe lung problems. You and your doctor will determine whether the possible benefits of Enhertu treatment for lung cancer outweigh the risk of other serious lung problems.

* For this use, Enhertu received accelerated approval from the Food and Drug Administration (FDA). This means its approval is based on information from early trials. The FDA will decide about full approval after more trials are completed.

What you can do

Your doctor will monitor you for symptoms of pneumonitis and ILD during your Enhertu treatment. You should watch for them as well. Possible symptoms can include cough, fever, shortness of breath, and any other change in breathing. If you develop any of these symptoms, talk with your doctor right away.

If you develop a serious lung condition, your doctor will likely have you stop Enhertu treatment. They may recommend a different drug to treat your condition.

Allergic reaction

As with most drugs, Enhertu can cause an allergic reaction in some people. However, this side effect wasn’t reported in clinical trials.

Symptoms can be mild or serious and can include:

  • skin rash
  • itching
  • flushing
  • swelling under your skin, typically in your lips, eyelids, feet, or hands
  • swelling of your mouth, tongue, or throat, which can make it hard to breathe

What you can do

For mild symptoms of an allergic reaction, call your doctor right away. They may recommend ways to ease your symptoms and determine whether you should keep receiving Enhertu. If your symptoms are serious and you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Enhertu has several precautions you should consider.

Boxed warnings

Enhertu has boxed warnings about risks of harm to a fetus and severe lung problems. These are serious warnings from the Food and Drug Administration (FDA).

For details about the risk of harm to a fetus, see “Pregnancy and breastfeeding while receiving Enhertu” below.

For details about the risk of severe lung problems, see the “Side effect specifics” section above.

Other precautions

Be sure to talk with your doctor about your health history before starting Enhertu treatment. This drug may not be right for you if you have certain medical conditions or other factors that affect your health. The conditions and factors to consider include:

Allergic reaction. If you’ve had an allergic reaction to Enhertu or any of its ingredients, your doctor will likely not prescribe Enhertu. Ask them about other medications that may be better options for you.

Heart problems. Severe heart problems, including heart failure, may occur with Enhertu. If you have or have had heart disease, talk with your doctor before starting treatment with the drug. Enhertu may increase your risk of heart-related side effects. Your doctor can advise you on whether the medication is right for you.

Breathing or lung condition. Enhertu can cause severe and life threatening lung problems. The drug has a boxed warning regarding this. If you have or have had a breathing or lung condition, talk with your doctor before you receive the medication. Enhertu may worsen your condition. See the “Side effect specifics” section above for more information.

Blood disorders. If you have or have had a blood disorder, such as neutropenia, talk with your doctor. The drug can lower the levels of certain blood cells, which may worsen your condition. Your doctor may monitor your blood test results more closely than usual while you receive Enhertu. Or they may recommend a different treatment.

Infection. If you currently have symptoms of an infection,you should not start receiving Enhertu. The drug may weaken your immune system, which can make it harder to fight infection. Your doctor can advise you on what treatment options are best for you.

Alcohol with Enhertu

Certain side effects of Enhertu, such as diarrhea or headache, can worsen if you drink alcohol during your treatment.

If you drink alcohol, talk with your doctor about how much, if any, is safe to consume with Enhertu.

Pregnancy and breastfeeding while receiving Enhertu

Here’s some information about pregnancy, breastfeeding, and Enhertu.

Enhertu and pregnancy

Enhertu has a boxed warning about the risk of harm to a fetus. A boxed warning is the most serious warning from the FDA. It alerts doctors and patients about drug effects that may be dangerous.

Enhertu treatment while pregnant may cause toxicity in the fetus. (Toxicity is the amount of a drug that’s unsafe.) This may cause congenital anomalies (commonly known as birth defects) or pregnancy loss. Your doctor will order a pregnancy test to make sure you aren’t pregnant before starting Enhertu treatment.

If you can become pregnant, you’ll need to use effective birth control while receiving Enhertu. You should continue to use birth control for at least 7 months after you have completed your Enhertu treatment.

If you decide to become pregnant after your Enhertu treatment has ended, talk with your doctor about when it’s safe to do so.

Enhertu and males

If you’re a male and your sexual partner can become pregnant, you should use birth control during Enhertu treatment. You should keep using birth control for at least 4 months after your last dose of Enhertu.

Keep in mind that based on findings from animal studies, Enhertu may cause fertility problems in males. (Fertility in males refers to the ability to make someone pregnant.) Your doctor can help address any concerns about how Enhertu may affect your fertility.

Note: Sex and gender exist on spectrums. Use of the term “male” in this article refers to sex assigned at birth.

Enhertu and breastfeeding

Whether Enhertu passes into breast milk is not known. Because of the risk of serious harm to a child who is breastfed, you should not breastfeed during Enhertu treatment. You should also not breastfeed for at least 7 months after receiving your last dose. This is because Enhertu can stay in your body for several months after your final treatment.

If you’re breastfeeding or planning to breastfeed, talk with your doctor. They can suggest healthy feeding options for your child and medications other than Enhertu.

If you’d like to learn more about Enhertu, talk with your doctor or pharmacist. They can help answer any questions you have about side effects from the drug. Here are a few questions you may want to discuss with your doctor or pharmacist:

  • Based on my health history, do I have a greater risk of developing certain side effects?
  • Are there other ways I can manage side effects from Enhertu?

Besides talking with your doctor, you can do some research on your own. These articles might help:

Disclaimer: Medical News Today 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.