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Trastuzumab deruxtecan (Enhertu®) A1373

Information leaflet on Trastuzumab deruxtecan (Enhertu®) A1373

This leaflet provides information for patients having treatment with Enhertu®. The leaflet will explain what Enhertu® is and when and how it is given. It will also tell you about common side effects that you may experience.  Contact telephone numbers and details of how to obtain further information on Enhertu® are given at the end of the leaflet.

This leaflet should be read alongside the general chemotherapy leaflet.  If you do not have one please ask.

What is Enhertu® and how does it work?

Enhertu® is made of 2 different drugs joined together in one drug: 

  1. A monoclonal antibody drug: this stops cancer cells from growing and dividing. It does this by attaching to HER-2 receptors.  HER-2 receptors are found on the outside of some cancer cells and stimulates the cancer cells to grow. 
  2. A chemotherapy drug: This stops all cells including cancer cells from growing and dividing    

How often will I receive Enhertu®?

For this treatment to be most effective, it is given at specific time intervals. It is usual to have Enhertu® every 3 weeks. The exact number of treatments you will receive will be discussed with you. 

How often will I see the specialist team?

We will let you know how often you will need to be reviewed, this will either be in the outpatient clinic or a telephone review. You will need a blood test before each treatment.  At each visit the nurse who gives your Enhertu® will check how you are feeling and discuss any problems you may have. 

How is Enhertu given?

Enhertu is given through a drip into a vein in the back of your hand or arm. However, sometimes, if your veins are difficult to find, it may be suggested that a fine tube called a PICC is inserted into a large vein in your upper arm. This will remain in place throughout the course of your treatment.  Your doctor or nurse will discuss this further with you, if required. We have a leaflet that tells you more about PICC lines.

Where will my treatment be given?

Your treatment may be in one of the day case treatment areas at Velindre or a hospital closer to your home.  

How long will my appointment take?

Your first Enhertu® is given more slowly to ensure that you do not have any reaction to the treatment.

You should allow approximately 3 hours for your first treatment and we will check that you are OK having it.

Your second Enhertu® treatment will be given slightly quicker. This appointment with take approximately up to 2 hours.

Can I bring a relative with me?

You are welcome to bring someone to stay with you during your treatment. Space is limited so there is not usually room for more than one person.  Treatment areas are not suitable for young children.

What are the possible side effects? 

Most people tolerate Enhertu® treatment very well, with very few side effects.  However, there are a number of possible side effects which can occur. The doctors, nurses and pharmacy team can give you advice or answer any questions you may have.

Reactions during the treatment 

Some patients may experience a reaction at the time the Enhertu® is given. This is why the first treatment is given more slowly.  A nurse will monitor you closely during the treatment. 

If you experience any of the following during the treatment please tell your nurse straight away:

  • Feeling hot and feverish
  • Develop a temperature
  • Chills or shivering
  • Headache
  • Dizziness or faintness
  • Problems with breathing
  • Rash or itching
  • Feeling sick or vomiting
  • Swelling of face/mouth ( this is rare) 
  • Pain in back, abdomen or chest

If any of these occur we will slow down or stop the Enhertu until you feel better. If needed, we will give you medication to help with the symptoms .The treatment can then start again, often without any further problems.

Sometimes patients can experience a temperature/shivering/feeling sick at home after the infusion on the first day. If this occurs, ring the treatment helpline. The telephone number is at the end of the leaflet. 


You are at an increased risk of picking up infections because your white blood cells which help fight infections can be reduced by this treatment.  

If you develop an infection whilst your white blood cells are low, you are at risk of sepsis, this can be life threatening. 

Contact Velindre Cancer Centre immediately if you develop any signs of infection, for example flu like symptoms or a temperature above 37.5°centigrade or below 35.5°centigrade.  The telephone number is at the end of the leaflet.

Lung problems (pneumonitis): 

A small number of patients may develop lung problems.  While this is rare if it is not treated quickly it can be very serious and potential life threatening.  If you already have lung problems please tell your Velindre team before you start treatment.
Once you start treatment if you feel short of breath, develop a new persistent cough or chest tightness ring the treatment helpline. The telephone number is at the end of the leaflet.

Skin and tissue damage

Some chemotherapy drugs may damage the skin and surrounding area if they leak outside of your vein.  This is known as extravasation.  It is extremely rare but it is important that you tell us immediately if you notice any swelling, pain or burning at the site of the drip.  If this occurs whilst the chemotherapy is being given, tell your nurse.  If you notice pain, swelling or redness when you’re at home please contact us immediately the telephone number is at the end of the leaflet

Heart problems

Enhertu® treatment may cause some heart problems. These will usually get better when Enhertu® treatment is stopped or has completed. Your doctor will discuss this with you and arrange for your heart function to be tested before you start Enhertu®. We will also check your blood pressure and monitor your weight regularly.  

If you already have a heart condition or you take any heart medication, please tell your Velindre doctor before you start treatment with Enhertu®. If you do develop heart problems whilst on Enhertu® it may be treated with tablets. It is very important not to stop taking any tablets you have been given for heart problems without discussing it with your Velindre doctor or specialist nurse. 

If at any time during your treatment you develop a new or worsening problem with shortness of breath- especially at rest, a cough, chest tightness, fluid retention (swelling) in your arms or legs, palpitations (heart flutter or irregular heart beat), feel dizzy or lightheaded, please contact the treatment helpline. The telephone number is at the end of the leaflet. 
However, if you experience any chest pain, ring 999.

Feeling sick: 

You can be sick with Enhertu® but we will give you anti-sickness medication before your treatment and will give you some to take home. This should prevent you from being sick.  It is important that you ring the treatment helpline if you feel sick and need anti-sickness medication or if the medication isn’t helping. 

Feeling feverish: 

If you feel shivery/cold/ feverish on the evening of your treatment, you can take paracetamol 4-6 hours apart, maximum of 8 in 24 hours. If you need 8 in 24 hours however, ring the treatment helpline. 

Other common side affects you may experience in the first few days after treatment include:


Diarrhoea may occur with Enhertu®. However, if you have 4 or more bowel movements in 24 hours above what is normal for you, contact Velindre Cancer Centre immediately.  The telephone number is at the end of the leaflet. 

Tiredness and fatigue 

You may feel more tired than usual.  It is important to listen to your body and rest if you need to, but carry out your normal activities if you feel able.  Some people find it beneficial to take gentle exercise as well as rest.


You may have headaches with this treatment. It is important you drink plenty of fluids preferably water.

Sore mouth

Your mouth may become sore and develop mouth ulcers. You may be prescribed mouthwash or other medication to help with this.

Anaemia and low platelets: 

If you feel tired, short of breath or notice excessive bruising or bleeding, ring the treatment helpline. 

Dry Eye

Enhertu® can sometimes cause dry eyes. It is important that you inform the team when they review you before your treatment. You may need eye drops. 

Blood clots

A diagnosis of cancer can increase your risk of developing a blood clot (thrombosis), and having cancer treatment may increase this risk further.  It is important to tell your doctor immediately if you have symptoms such as pain, redness and swelling in your leg, or breathlessness and chest pain.  

Blood clots can be very serious.  However, most clots can usually be successfully treated with drugs to thin the blood.  Your doctor or nurse can give you more information.

Other information

It is important you do not become pregnant whilst having Enhertu® treatment, and for 7 months after completing the treatment. Breastfeeding is not recommended during treatment and for a minimum of 7 months following completion of treatment.  Men should use effective contraception for a least 4 months after completing treatment.

Taking other medication with Enhertu®?

Enhertu® can remain in your body for up to 6 months after you finish treatment.  During this time you should tell your doctor or pharmacist that you have had Enhertu® before starting any new medicines.
Do not take over the counter medication, herbal or alternative medicines. 

Sometimes cancer drugs can have very serious side effects which rarely can be life threatening. It is important to inform Velindre cancer centre if you are concerned about any side-effects.  The telephone number is at the end of the leaflet.

Manufacturer’s patient information leaflets

Velindre leaflets provide information about very common and commonly reported side-effects (we are unable to list all of the common side effects), for more information regarding these and the less common side-effects please refer to the manufacturers patient information leaflets, obtained from Velindre pharmacy and/or on the internet at Sometimes patients may find these leaflets difficult to read however. Please ask if you would like a copy from your doctor or from Velindre pharmacy

Contact telephone numbers

Velindre Cancer Centre        029 2061 5888
If you are unwell at home and need immediate advice at any time of the day or night ask for the treatment helpline

Pharmacy department         029 2061 5888 ext 6223
Monday – Friday 9am – 5pm for queries about your medicines

Macmillan freephone Helpline     0808 808 0000

Tenovus freephone                 0808 808 1010
cancer helpline 

This information is also available in Welsh

This leaflet was written by health professionals.  The information contained in this leaflet is evidence based.  The leaflet has been approved by doctors, nurses, pharmacists and patients.  It is reviewed and updated every 2 years.

Written June 2021

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