What is pembrolizumab (Keytruda®)?

Pembrolizumab (Keytruda®) is used to treat:

It may sometimes be used to treat other cancers. It is best to read this information with our general information about the type of cancer you have.

Pembrolizumab is an immunotherapy drug. It may also be called a checkpoint inhibitor. Your doctor will talk to you about this treatment and the possible side effects before you agree (consent) to have treatment.

How pembrolizumab is given

You are given pembrolizumab at a day unit as an outpatient. Pembrolizumab can be given on its own, or with other cancer drugs.

During treatment you usually see a cancer doctor, a specialist nurse, and a specialist pharmacist. This is who we mean when we mention doctor, nurse or pharmacist in this information.

Before, or on the day of, treatment, a nurse or person trained to take blood (phlebotomist) may take a blood sample from you.

You see a doctor or nurse before you have treatment. They will talk to you about your blood results and ask you how you have been feeling. If your blood results are okay, the pharmacist will prepare your treatment.

A nurse gives you pembrolizumab into a vein as a drip (intravenous infusion). The drip is usually run through a pump, which gives you the treatment over a set time. It is given over about 30 minutes.

Your course of treatment

You may have pembrolizumab every 3 weeks, or every 6 weeks. You usually keep having it for as long as it is working. Your doctor, nurse or pharmacist will discuss your treatment plan with you.

About side effects

We explain the main side effects of this treatment here. We also include some other possible side effects.

You may get some of the side effects we mention, but you are unlikely to get all of them. If you are also having treatment with other cancer drugs, you may have some side effects that we have not listed here. Always tell your doctor, nurse or pharmacist about any side effects you have.

Your doctor can give you drugs to help control some side effects. It is important to take them exactly as your nurse or pharmacist explains. This means they will be more likely to work for you. Your nurse will give you advice about managing your side effects. After your treatment is over, most side effects start to improve.

Serious or delayed side effects

Some cancer treatments can cause severe side effects. Rarely, these may be life-threatening. Your doctor or nurse can explain the risk of these side effects to you.

This treatment may cause delayed side effects. These can start weeks, months, or sometimes more than a year, after you finish treatment.

If you have any symptoms or side effects that start during treatment or after treatment finishes, contact your doctor or hospital straight away. Side effects can become serious if they are not treated.

Your patient alert card

Your doctor, nurse or pharmacist will give you a card with information about your treatment on it. It is important to always have the card with you during treatment and after treatment finishes. You should show it to any doctor or healthcare professional you need to see.

Contact the hospital

Your nurse will give you telephone numbers for the hospital. If you feel unwell or need advice, you can call at any time of the day or night. Save these numbers in your phone or keep them somewhere safe.

Sometimes side effects can become serious very quickly. It is important to contact the hospital straight away if you have new symptoms or side effects.

More information

We cannot list every side effect for this treatment. There are some rare side effects that are not listed. You can visit the electronic Medicines Compendium (eMC) for more detailed information.

Side effects while treatment is being given

Some people may have side effects while they are being given the treatment or shortly after they have it:

Allergic reaction

Some people have an allergic reaction while having this treatment. Signs of a reaction can include:

  • feeling hot or flushed
  • a skin rash
  • itching
  • shivering
  • feeling dizzy
  • a headache
  • feeling breathless
  • swelling of your face or mouth
  • pain in your back, tummy or chest.

Your nurse will check you for signs of a reaction during your treatment. If you feel unwell or have any of these signs, tell them straight away. If you do have a reaction, it can be treated quickly.

Sometimes a reaction can happen a few hours after treatment. If you get any signs or feel unwell after you get home, contact the hospital straight away.

Main side effects

Some of these side effects are rare. But it is important to know about them. They can become serious if you try to treat them yourself. Always contact your doctor or the hospital straight away if you have these side effects during treatment or after it finishes.

Diarrhoea or tummy pain

You may have diarrhoea or tummy pain.

Contact the hospital straight away if you have any of these symptoms during treatment or after it finishes:

  • passing stools (pooing) more than 4 times a day
  • waking up at night to pass stools
  • pain in your tummy (abdomen)
  • being sick
  • blood or mucus in your stools
  • a fever, with a temperature over 37.5°C (99.5°F).

You may need to go into hospital to have fluids through a drip (infusion) or other treatments, such as steroids.

Effects on the lungs

This treatment can cause changes to the lungs. Contact the hospital straight away if you notice any of these changes during treatment or after it finishes:

  • breathlessness
  • a cough
  • wheezing
  • a fever, with a temperature over 37.5°C (99.5°F).

You should also tell them if any existing breathing problems get worse. You may have tests to check your lungs. You may need steroids or other treatments.

Skin changes

This treatment may cause skin changes, including:

  • a rash
  • itching
  • patches of white or paler skin.

If you are out in the sun, use a sun cream with a high sun protection factor (at least SPF 30) to protect your skin. Always tell your doctor or nurse straight away if you notice any skin changes during treatment or after it finishes. You may need creams, steroids or other medicines. Your doctor may stop your treatment until the skin changes improve.

Rarely, a much more serious skin condition can develop. You may have a skin rash which then blisters, and your skin can peel. You may also feel unwell with flu-like symptoms such as a high temperature and joint pain. If you have any of these symptoms, contact your doctor or hospital immediately.

Muscle and joint pain

This treatment can cause sore or weak muscles and stiff, sore or swollen joints. Contact your doctor straight away if you have any of these symptoms during treatment or after it finishes:

  • new aches or pains
  • new stiffness in a joint
  • swollen or red joints.

You may need steroids or other treatments such as painkillers.

Hormone changes

This treatment may affect how your body makes hormones. Hormones control many different processes in the body. You will have regular blood tests to check some of your hormone levels. Your doctor may give you drugs to control your hormone levels, and to reduce the risk of side effects such as:

  • increased sweating
  • weight gain or weight loss
  • dizziness or fainting
  • feeling more hungry or thirsty than usual
  • loss of sex drive
  • passing urine (peeing) more often than usual
  • headaches that do not go away.

If you have any of these symptoms during treatment or after it finishes, tell your doctor straight away.

Effects on the liver

This treatment can affect how your liver works. You will have regular blood tests to check this. Your doctor may give you steroids if the blood tests show liver changes.

Sometimes liver changes can be serious. Contact the hospital straight away if you have any of these symptoms during treatment or after it finishes:

  • yellow skin or eyes
  • feeling very sleepy
  • dark urine (pee)
  • unexplained bleeding or bruising
  • loss of appetite.

You may need steroids or other treatments, and may be monitored until your liver recovers.

Weakness, numbness and tingling

This treatment can affect the nerves. This is not common but can become serious if it is not treated. These side effects may be mild to start with. Contact your doctor straight away if you have any of these symptoms during treatment or after it finishes:

  • problems fastening buttons or doing other fiddly tasks
  • any weakness, numbness or tingling in your arms, legs or face
  • headaches
  • any unexplained pain in other parts of your body.

You may need steroids and other treatments.

Effects on the kidneys

This treatment can affect how your kidneys work. This is not common but can become serious if it is not treated. You will have regular blood tests to check how your kidneys are working. Your doctor may give you steroids or other treatments if tests show kidney changes.

Contact the hospital straight away if you have either of these symptoms during treatment or after it finishes:

  • not passing urine (peeing)
  • only passing very small amounts of urine.

Raised blood sugar levels

This treatment may raise your blood sugar levels. You will have regular blood tests to check this. Symptoms of raised blood sugar include:

  • feeling thirsty
  • needing to pass urine (pee) more often
  • feeling tired.

Tell your doctor or nurse if you have these symptoms during treatment or after it finishes.

If you have diabetes, your blood sugar levels may be higher than usual. Your doctor will talk to you about how to manage this.

Eyesight changes

This treatment can affect your eyes and eyesight. If you have any of these symptoms during treatment or after it finishes, contact your doctor straight away:

  • sore or swollen eyes
  • eyes that are sensitive to light
  • changes to your eyesight.

You may need steroids or other treatments. You may also have an eye check with a specialist eye doctor (ophthalmologist).

Effects on the heart

This treatment can affect the way the heart works. This is not common, but can be serious. You may have tests to see how well your heart is working. These may be done before, during, and sometimes after treatment.

Contact your doctor straight away if you have any of these symptoms during treatment or after it finishes:

  • pain or tightness in your chest
  • feeling breathless or dizzy
  • feeling that your heart is beating too fast or too slowly.

If your symptoms are caused by this treatment, you may need steroids. You may be monitored in hospital for a time. Other conditions can cause these symptoms, but it is important to get them checked straight away.

Other possible side effects

Feeling sick

If you feel sick, take small sips of fluids and try to eat small amounts often. Your doctor can prescribe anti-sickness drugs. Take the drugs exactly as your nurse or pharmacist explains to you. If you continue to feel sick, contact the hospital. They will give you advice and may change the anti-sickness drug to one that may work better for you.

Loss of appetite

This treatment can affect your appetite. Do not worry if you do not eat much for a day or two. But if your appetite does not come back after a few days, tell your nurse or dietitian. They will give you advice. They may give you food or drink supplements.

Constipation

This treatment can cause constipation. Here are some tips that may help:

  • Drink at least 2 litres (3½ pints) of fluids each day.
  • Eat high-fibre foods, such as fruit, vegetables and wholemeal bread.
  • Do regular gentle exercise, like going for short walks.

If you have constipation, contact the hospital for advice. Your doctor can give you drugs called laxatives to help.

Feeling tired

Feeling tired is a common side effect. But sometimes tiredness is a sign that treatment is affecting your hormone levels or nerves, and you may need treatment.

Contact your doctor straight away if you have either of these symptoms during treatment or after it finishes:

  • tiredness that gets worse
  • feeling weak or shaky.

If you feel sleepy, do not drive or use machinery.

Anaemia (low number of red blood cells)

This treatment can reduce the number of red blood cells in your blood. These cells carry oxygen around the body. If the number of red blood cells is low, you may be tired and breathless. Tell your doctor or nurse if you feel like this. If you are very anaemic, you may need a drip to give you extra red blood cells. This is called a blood transfusion.

Headaches

This treatment may cause headaches. If this happens, tell your doctor or nurse. They can give you painkillers.

Fluid build-up

You may gain weight, or your face, ankles and legs may swell. This improves slowly after your treatment has finished. Your doctor may give you drugs to help reduce the swelling.

Less common side effects

Low number of white blood cells

This treatment can reduce the number of white cells in your blood. These cells fight infection. Tell your doctor or nurse if you have any signs of an infection. These include:

  • a cough
  • a sore throat
  • diarrhoea
  • needing to pass urine (pee) often.

Contact your doctor or the hospital straight away if:

  • your temperature goes over 37.5°C (99.5°F)
  • you suddenly feel unwell, even with a normal temperature

Bruising and bleeding

This treatment can reduce the number of platelets in your blood. Platelets are cells that help the blood to clot. 

Tell your doctor if you have any bruising or bleeding that you cannot explain. This includes:

  • nosebleeds
  • bleeding gums
  • tiny red or purple spots on the skin that may look like a rash.

Some people may need a drip to give them extra platelets. This is called a platelet transfusion.

Dry mouth

You may get a dry mouth. Drink plenty of fluids and add sauces and gravies to your food to keep it moist. If you have dry lips, using a lip balm can help.

Changes to your taste

You may get a bitter or metal taste in your mouth. Sucking sugar-free sweets may help with this. Some foods may taste different or have no taste. Try different foods to find out what tastes best to you. Taste changes usually get better after treatment finishes. Your nurse can give you more advice.

Helpful hints to improve taste

  • Season food or add spices and herbs to add flavour when cooking.
  • Use strong, flavoured sauces or gravies to make food tastier.
  • Eat sharp-tasting fresh fruit and juices or try sugar-free sweets to leave a pleasant taste in your mouth.
  • Try cold foods as they may have a stronger taste than hot foods.

High blood pressure

This treatment can cause high blood pressure. Tell your doctor or nurse if you have ever had any problems with your blood pressure. Your nurse will check it regularly during your treatment. Let them know if you have any headaches.

Other information about pembrolizumab

Driving

Do not drive if you feel dizzy or tired, or if your vision is affected. Talk to your doctor if you are not sure whether it is safe for you to drive.

Other medicines

Some medicines can affect how this treatment works or be harmful when you are having it. Always tell your cancer doctor about any drugs you are taking or planning to take, such as:

  • medicines you have been prescribed
  • medicines you buy in a shop or chemist
  • vitamins, herbal drugs and complementary therapies.

Tell other doctors, pharmacists or dentists who prescribe or give you medicines that you are having this cancer treatment.

You can visit the electronic Medicines Compendium (eMC) for more detailed information about your treatment.

Vaccinations

Vaccinations can reduce your risk of getting certain infections. Your doctor or nurse may talk to you about having vaccinations.

Doctors usually recommend that people with cancer have a flu vaccination and a coronavirus vaccination. These are both inactivated vaccinations that can help reduce the risk of infection. People with weak immune systems can have these, as they are not live vaccinations.

If your immune system is weak, you need to avoid live vaccinations. This is because they can make you unwell. Live vaccines, such as shingles, contain a very weak version of the illness they are vaccinating you against. Your cancer doctor or GP can tell you more about live and inactivated vaccinations.

Contraception

Your doctor will advise you not to get pregnant or make someone pregnant while having this treatment. The drugs may harm a developing baby. It is important to use contraception during your treatment and for a while after treatment finishes. Your doctor, nurse or pharmacist can tell you more about this.

Breastfeeding

Women are advised not to breastfeed while having this treatment. This is because the drugs could be passed to the baby through breast milk.

Fertility

Some cancer drugs can affect whether you can get pregnant or make someone pregnant. If you are worried about this, it is important to talk with your doctor before you start treatment.

Medical and dental treatment

If you need medical treatment for any reason other than cancer, always tell the doctor and nurse that you are having cancer treatment. Show them your Patient Alert Card. Give them the contact details for your cancer doctor so they can ask for advice.

If you think you need dental treatment, talk to your cancer doctor or nurse. Always tell your dentist you are having cancer treatment.