Side Effects
Like all medicines, KEYTRUDA (pembrolizumab) can cause side effects. Although not everyone gets them, it is important to look out for any signs and/or symptoms. Do not wait until your next appointment. If you notice any symptoms, you should let your healthcare team know straight away. This will help your doctor treat these side effects early and may prevent them from getting worse. Your doctor may give you other medicines to prevent more severe complications and reduce your symptoms.
Many of the possible side effects can be managed without having to permanently stop your treatment. Your doctor will decide how to best manage your side effects. Do not try to diagnose or treat side effects yourself. Always carry your pembrolizumab Patient Alert Card with you at all times and show it to any healthcare professional who treats you. Remember to read the Patient Information Leaflet for all your medicines.
Before you are treated with pembrolizumab, tell your doctor if you:
- have an autoimmune disease (a condition where the body attacks its own cells)
- have pneumonia or inflammation of your lungs (called pneumonitis)
- were previously given ipilimumab, another medicine for treating melanoma, and experienced serious side effects because of that medicine
- had an allergic reaction to other monoclonal antibody therapies
- have or have had chronic viral infection of the liver, including hepatitis B (HBV) or hepatitis C (HCV)
- have human immunodeficiency virus (HIV) infection or acquired immune deficiency syndrome (AIDS)
- have liver damage
- have kidney damage
- have had a solid organ transplant or a bone marrow (stem cell) transplant that used donor stem cells (allogeneic).
Understanding Possible Side Effects
Like all medicines, pembrolizumab can cause side effects. Although not everybody gets them, it is important to look out for any signs and/or symptoms. If you get any side effects, talk to your doctor straight away. This includes any possible side effects even if listed in the Pembrolizumab Patient Information Leaflet.
Being Aware
Your healthcare team should have provided you with materials to help you identify possible side effects you may experience during your treatment.
Tell your healthcare professional immediately about any changes to how you are feeling. Do not attempt to diagnose or treat side effects yourself. Reporting side effects early may stop them from becoming more serious and can make them easier to treat. They may be managed without having to permanently come off treatment and your healthcare professional will be able to better support you.
DO NOT ATTEMPT TO DIAGNOSE OR TREAT SIDE EFFECTS BY YOURSELF
List of Some Possible Side Effects
Below is a list of some possible side effects that you should look out for. If you get any side effects (including any not on the list), talk to your doctor immediately. Not all side effects can be easily recognised, but knowing what side effects are possible with your treatment can help you to notice them when they happen. For this reason, you should familiarise yourself with the pembrolizumab Patient Information Leaflet (PIL).
Below is a list of some signs or symptoms for possible side effects that you should look out for. Side effects may happen anytime during treatment or even after your treatment has ended. You may experience more than one side effect at the same time. If you notice any symptoms, even if not listed below, while receiving your treatment, you should speak to your healthcare professional right away – telling your healthcare professional IMMEDIATELY once you notice any symptoms may stop them from becoming more serious. Do NOT wait for your next appointment. Reporting side effects early can make them easier to treat.
- My eyesight has changed
- I have loss of vision
- My eyes hurt or feel uncomfortable
- I have noticed a yellowing of my eyes
- I have noticed uncomfortable sensitivity to light or seeing spots
- I am more thirsty than usual
- I have a dry mouth
- My sense of taste has changed
- I have a sweet or metallic taste in my mouth
- I have a sweet smell to my breath
- I feel faint or dizzy
- I have headaches that will not go away or are unusual for me
- I have noticed changes to my skin or hair
- I have noticed changes in the colour of my skin
- I have developed a rash or my skin is itchy or dry
- I have skin blistering, peeling or sores
- I have ulcers in my mouth or in the lining of my nose, throat, or genital area
- I am bleeding or bruising more easily than normal
- I am sweating more than normal
- My sweat has a different odour
- My hair is falling out
- I have developed a new or worse cough
- My voice is getting deeper
- I feel more short of breath
- My breathing is faster and deeper
- I have chest pain
- I have noticed a rapid or irregular heartbeat
- The amount, odour or colour of my urine has changed
- I need to urinate more often
- I have urinary incontinence or difficulty urinating
- It is painful when I urinate
- I have blood in my urine
- I feel less or more hungry than usual
- I have been nauseous or vomiting
- I am constipated
- I have diarrhoea or more bowel movements than usual
- My stools are black, tarry, sticky or have blood or mucus
- My stomach area feels sore or tender
- I have pain or pressure in my lower abdomen
- I have a stiff neck
- There is swelling or pain in my legs or arms
- I have muscle cramps, spasms, pain or weakness
- I have joint pains
- I feel numbness, burning, tingling and/or paralysis in my arms or legs
- I feel more tired or confused
- I have memory problems
- I have seizures
- I have trouble sleeping
- I feel unusually sleepy
- I feel colder than normal
- I have chills or flu-like illness
- I have a fever or have hot flushes
- I have lost or gained weight
- I am feeling generally unwell
- I have a reaction related to the infusion of the medicine
What Do I Do If Symptoms Occur
It is important to contact your healthcare professional as soon as symptoms occur. Always carry your pemberolizumab Patient Alert Card which contains important information about reporting any signs of symptoms (including those not listed) immediately to your healthcare professional treating you while you are away from home. It is also important to tell other healthcare professionals that you are being treated with pembrolizumab. Certain medications, such as corticosteroids, may be prescribed to you by your healthcare professional to help manage your adverse events, reduce your symptoms and prevent severe complications. Your healthcare professional may delay or completely stop your treatment if your side effects are too severe.
Always carry your patient alert card, and DO NOT ATTEMPT to diagnose or treat side effects yourself
References:
- KEYTRUDA Patient Information Leaflet.
Supporting documentation
KEYTRUDA® (pembrolizumab)
Summary of Product Characteristics | Patient Information Leaflet
GB-PDO-03632 | Date of Preparation: July 2025
Merck Sharp & Dohme (UK) Limited Registered Office: 120 Moorgate, London, EC2M 6UR, United Kingdom.
Registered in England No. 233687 © 2025 Merck & Co., Inc., Rahway, NJ, USA and its affiliates. All rights reserved.
GB-NON-11683 | Date of Preparation: July 2025
Reporting of side effects: If you get any side effects, talk to your doctor, pharmacist or nurse. This includes any possible side effects not listed in the package leaflet. You can also report side effects directly via the Yellow Card Scheme at https://yellowcard.mhra.gov.uk/. By reporting side effects, you can help provide more information on the safety of this medicine.