Also known as pembrolizumab

Key points about Keytruda

  • Keytruda (key-true-duh) is a medicine used to treat certain cancers.
  • Find out how it's given and possible side effects. 
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Keytruda is a medicine that's used to treat certain cancers by working with your body's immune system to detect and destroy cancer cells (called immunotherapy). Keytruda belongs to a group of medicines called immune checkpoint inhibitors. Read more about immune checkpoint inhibitors and how they work.   

In Aotearoa New Zealand, Keytruda is funded for treating metastatic melanoma in people who meet the eligibility criteria.

From 1 April 2023, Keytruda is also funded for the treatment of advanced or metastatic non-small cell lung cancer (NSCLC) for people who meet the eligibility criteria.

Keytruda is given as an intravenous (IV) injection through a vein over 30 minutes (infusion) every 3 or 6 weeks. The dose of Keytruda you will be given depends on many factors, including your weight, your general health or other health problems, and the type of cancer being treated. Your doctor will work out your dose and schedule.

During the infusion

Most people have few side effects during the infusion. On rare occasions Keytruda can cause a reaction while it's being given. This usually happens within 30 minutes to 2 hours after starting the first infusion. You may experience fever, chills, flushing, skin rash, itching, dizziness headache or have trouble breathing.

Tell the nurse immediately if any of these symptoms occur. This reaction is usually mild and can sometimes be controlled by giving Keytruda more slowly. 

Before starting Keytruda, tell your doctor about any other medicines you are taking including prescription, over-the-counter, vitamins, or herbal remedies.

Tell your doctor if you're pregnant or may be pregnant before starting Keytruda. Keytruda isn't recommended for use during pregnancy. You should avoid becoming pregnant while you are on Keytruda. Use effective birth control during treatment and for at least 4 months after your final dose of Keytruda. Ask your doctor when you may safely become pregnant after therapy. 

Tell your doctor if you're breastfeeding or plan to breastfeed. It is advised not to breastfeed during treatment with Keytruda and for 4 months after your final dose.


  • Since Keytruda affects your immune system, you are at increased risk of infection. It's strongly advised that you're up-to-date with the annual flu vaccination and the Covid-19 vaccinations. These are non-live vaccines and they're safe to have while you are receiving immune checkpoint inhibitor treatment.
  • Live vaccines such as MMR (measles, mumps and rubella) and varicella (chickenpox vaccine) should NOT be given while you are receiving immune checkpoint inhibitor treatment and for 6 months after treatment has stopped.

Treatment delays

There may be times when your treatment is delayed. This can happen:

  • if your doctor thinks you may have severe side effects
  • if you get severe side effects
  • if your blood counts are affected
  • if you're finding it hard to cope with the treatment.

Your doctor will tell you if you need any delays to your treatment and the reason why.

Like all medicines, Keytruda can cause side effects, although not everyone gets them. Because Keytruda affects the immune system, it may cause immune cells to attack healthy cells, triggering a variety of side effects.

You may experience side effects at any time during your treatment or even months after treatment has finished. Some side effects go away within a few days or weeks and some may be longer lasting. 

Note: To monitor your side effects, you will need regular reviews and blood tests to check your liver, kidneys and blood before you start treatment and regularly while you are receiving treatment. 

Common side effects

Report any side effects to your healthcare provider straight away even if they appear mild.  Do not manage these side effects on your own:

  • feeling very tired and weak (fatigue)
  • cough
  • feeling sick (nausea)
  • runny poo (diarrhoea)
  • decreased appetite
  • headache
  • skin rash, itch, loss of skin pigmentation (vitiligo).
Rare, serious side effects

In some people, these side effects could be life threatening. If you have any of the side effects mentioned below OR any new or worsening symptoms, contact your healthcare team or Healthline on 0800 611 116 straight away:

  • Dark urine, and pale poo with yellowing of the eyes or skin (signs of inflamed liver).
  • Weight loss, weight gain, changes in mood, changes in eyesight and vision, increased sensitivity to cold or heat, slow or rapid heart rate, hair loss (possible signs of thyroid problems).
  • New or worsening cough, shortness of breath, and chest pain (possible signs of an inflamed lung or heart).
  • Blood in your poo, severe pain in your tummy or back (possible signs of an inflamed gut or pancreas).
  • Neck stiffness, headache, vomiting, eye sensitivity to light, confusion and sleepiness (signs of inflammation of the brain or spinal cord). 
  • Muscle weakness, numbness or tingling in hands and feet (signs of problems with your nerves).
  • Swelling or burning feeling on your skin, ulcers in your mouth or lips, genital or anal areas, purple spots on the skin, blisters or peeling (signs of a severe skin reaction).

Note: This is not a full list of side effects and side effects can vary in different people. If you don't know whether your symptoms are side effects of the medicine, contact your healthcare team straight away.

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Credits: Healthify He Puna Waiora editorial team. Healthify is brought to you by Health Navigator Charitable Trust.

Reviewed by: Healthify clinical advisors

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