Decorative image

Pembrolizumab (Keytruda)

Pembrolizumab (pronounced pem-bro-lee-zoo-mab) is also known by its brand name, Keytruda. 

It is a treatment for some people with:

  • non small cell lung cancer (NSCLC)
  • melanoma skin cancer
  • Hodgkin lymphoma

You might also have pembrolizumab as part of a clinical trials for another type of cancer. 

How it works

Pembrolizumab is a type of immunotherapy. It stimulates the body's immune system to fight cancer cells. 

Pembrolizumab targets and blocks a protein called PD-1 on the surface of certain immune cells called T-cells. Blocking PD-1 triggers the T-cells to find and kill cancer cells.

How you have it

You have pembrolizumab as a drip into a vein (intravenously).

Into your bloodstream

You have the treatment through a drip into your arm. A nurse puts a small tube (a cannula) into one of your veins and connects the drip to it.

You might need a central line. This is a long plastic tube that gives the drugs into a large vein, either in your chest or through a vein in your arm. It stays in while you’re having treatment, which may be for a few months.

When you have it

You have the treatment over 30 minutes, every 3 weeks. You might have pembrolizumab for up to 2 years as long as it works and the side effects are not too bad.

Some people might have treatment for longer than 2 years.

Tests during treatment

You have blood tests before starting treatment and during your treatment. They check your levels of blood cells and other substances in the blood. They also check how well your liver and kidneys are working.

Side effects

We haven't listed all the side effects. Your doctor or nurse will talk to you about the possible side effects. Tell your doctor or nurse if you notice anything unusual or different during and after treatment.

When to contact your team

Your doctor and nurse will monitor you closely for any side effects. Let your doctor or nurse know as soon as possible if:

  • you have severe side effects 
  • your side effects aren’t getting any better
  • your side effects are getting worse

Early treatment can help manage side effects better. 

Common side effects

Each of these effects happens in more than 1 in 10 people (10%). You might have one or more of them. They include:

Feeling or being sick (nausea)

Feeling or being sick is usually well controlled with anti sickness medicines. Avoid eating fatty or fried foods, eat small meals and snacks, drink plenty of water and relaxation techniques all can help.

Pain and swelling in your joints

Let your doctor or nurse know if you have pain in your joints during or after having treatment. There are lots of ways to treat pain, including relaxation and painkillers.


You might have diarrhoea, that is 4 loose watery poos (stools) in 24 hours. 

Contact your doctor or nurse straight away if you have any signs of diarrhoea or you open your bowels more often than usual.

You might also have:

  • black, tarry, sticky poo
  • blood or mucus in your poo
  • severe tummy pain or tenderness
  • feeling or being sick

Your medical team will tell you what to do.  Depending on how severe your symptoms are, you might need treatment such as anti diarrhoea medicine and fluids into your vein. You may stop treatment for a time or stop altogether.

Make sure you drink plenty. Ask your nurse about soothing creams to apply around your back passage (anus). The skin in that area can get very sore and even break if you have severe diarrhoea.

Skin changes

You might notice skin changes, such as dryness, itching and rashes similar to acne on your face, neck and trunk. 

Tell your doctor if you have any rashes or itching. Don't go swimming if you have a rash because the chlorine in the water can make it worse.

If your skin gets dry or itchy, smoothing in unperfumed moisturising cream may help. Check with your doctor or nurse before using any creams or lotions. Wear a high factor sun block if you’re going out in the sun.

Tiredness and weakness (fatigue)

You might feel very tired and as though you lack energy.

Various things can help you to reduce tiredness and cope with it, for example exercise. Some research has shown that taking gentle exercise can give you more energy. It is important to balance exercise with resting.

Occasional side effects

Each of these effects happens in more than 1 in 100 people (1%). You might have one or more of them. They include:

  • tiredness and looking pale
  • loss of appetite
  • taste changes
  • dry mouth
  • headaches
  • dry eyes
  • feeling dizzy
  • breathlessness, cough or chest pain
  • tummy (abdominal) pain
  • constipation
  • changes to your skin colour
  • flu like symptoms
  • swelling of your arms and legs
  • changes to your thyroid
  • liver changes
  • allergic reaction

Rare side effects

Each of these effects happens in fewer than 1 in 100 people (1%). You might have one or more of them. They include:

  • inflammation of your liver or pancreas
  • type 1 diabetes
  • infections
  • difficulty sleeping
  • muscle weakness (myasthenia)
  • yellow skin and eyse
  • kidney problems
  • bruising, bleeding gums and nosebleeds
  • numbness or tingling in finger and toes
  • weakness of hands and feet
  • hair loss
  • inflammation of the eye
  • high blood pressure
  • skin problems
  • a hole in your small bowel
  • inflammation of your nerves
  • changes to your hormone levels

Information about side effects

We have more information about side effects and tips on how to cope with them.

What else do I need to know

Other medicines, foods and drink

Cancer drugs can interact with some other medicines and herbal products. Tell your doctor or pharmacist about any medicines you are taking. This includes vitamins, herbal supplements and over the counter remedies.

Pregnancy and contraception

This drug may harm a baby developing in the womb. It is important not to become pregnant or father a child while you are having treatment with this drug and for at least 4 months afterwards. Talk to your doctor or nurse about effective contraception before starting treatment.


We don’t know how this treatment might affect fertility. You may not be able to become pregnant or father a child after treatment with this drug. Talk to your doctor before starting treatment if you think you may want to have a baby in the future.

Some men might be able to store sperm before starting treatment. Some women might be able to store eggs or embryos before treatment.


Don’t breastfeed during this treatment because the drug may come through in your breast milk.

Treatment for other conditions

Always tell other doctors, nurses, pharmacists or dentists that you’re having this treatment if you need treatment for anything else, including teeth problems.


Don’t have immunisations with live vaccines while you’re having treatment and for at least 6 months afterwards.

In the UK, live vaccines include rubella, mumps, measles, BCG, yellow fever and shingles vaccine (Zostavax).

You can:

  • have other vaccines, but they might not give you as much protection as usual
  • have the flu vaccine (as an injection)
  • be in contact with other people who've had live vaccines as injections

Avoid close contact with people who’ve recently had live vaccines taken by mouth (oral vaccines) such as oral polio or the typhoid vaccine.

This also includes the rotavirus vaccine given to babies. The virus is in the baby’s poo for up to 2 weeks and could make you ill. So, avoid changing their nappies for 2 weeks after their vaccination if possible. Or wear disposable gloves and wash your hands well afterwards.

You should also avoid close contact with children who have had the flu vaccine nasal spray if your immune system is severely weakened. 

More information about this treatment

For further information about this treatment go to the electronic Medicines Compendium (eMC) website.

You can report any side effect you have to the Medicines Health and Regulatory Authority (MHRA) as part of their Yellow Card Scheme.

iWantGreatCare lets patients leave feedback on their experience of taking a particular drug. The feedback is from individual patients. It is not information, or specialist medical advice, from Cancer Research UK.

Information and help

Dangoor sponsorship

About Cancer generously supported by Dangoor Education since 2010.