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Let's learn about the Pembrolizumab vaccine used to treat cancer.

MBBS
Medically Reviewed by MBBS ✓ Medically Reviewed
📅 Updated: Jul 14, 2026 • ⏱ 6 min read • Editorial policy
Let's learn about the Pembrolizumab vaccine used to treat cancer.
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When you find out that you or someone close to you has cancer, it's normal to feel curious, and perhaps even nervous, about the treatment options. It can be scary, especially when you hear about new, complicated medications. Today we're going to talk about one such new cancer treatment, Pembrolizumab. Let's talk in a simple, friendly way about what's really going on and what we need to be aware of.

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What is Pembrolizumab?

Simply put, Pembrolizumab is a drug that is used to treat several specific types of cancer . It is known in the market as Keytruda. This is not like a regular drug, it belongs to a type of monoclonal antibody.

Imagine, our own body has an army that protects us from disease, we call it the immune system. Sometimes cancer cells are very cunning, they hide from this immune army. What Pembrolizumab does is give our immune system a signal, "Wake up, there's an enemy here," and help it find cancer cells and attack them. That is, it is a way to use our own defense system to fight cancer.

Things you need to tell your doctor before starting treatment

It is very important to tell your doctor about your complete health history, as this medicine is not the same for everyone. Be sure to tell your doctor about these things in particular:

  • Immune system diseases: If you have autoimmune diseases, such as Crohn's disease, ulcerative colitis, or lupus, in which the body's immune system attacks its own cells.
  • Organ transplants: If you have previously had an organ transplant or if you have had or are planning to have an allogeneic stem cell transplant.
  • Other medical conditions: If you have had radiation treatment to the chest area, or if you have a nervous system disease, such as myasthenia gravis or Guillain-Barre syndrome.
  • Allergies: If you have an allergy to this medicine, Pembrolizumab, or any other medicine, food, or dye.
  • Pregnancy and breastfeeding: If you are pregnant, trying to get pregnant, or breastfeeding, it is important to tell your doctor. This is very important.

How can I give you this medicine?

This medicine is not something you can take home.

This is an infusion that is given into a vein, like saline. That means it is given to you by trained medical staff in a hospital or clinic.

Before each treatment session, you will be given a special information leaflet (MedGuide) about this medicine. It is very important for your safety to always read and understand it carefully.

This medicine is also recommended for children over 6 months of age in some special cases. However, special care should be taken, so discuss it carefully with your doctor.

What if I take too much medicine?

This is a hospital-based drug, so the chances of this happening are low. However, if you think you have taken too much of this medicine, go to a hospital's Emergency Unit (ETU) immediately . Or call the National Poisons Information Centre at the Colombo National Hospital for advice.

What if I miss a treatment session?

It is very important to take this medicine on the scheduled date and time. If you are unable to go to the hospital on the scheduled date, call your doctor immediately and let them know so they can advise you on what to do next.

What are the possible side effects?

Like any medicine, Pembrolizumab can have side effects. But not everyone gets them. It's important to be aware of these. Let's break these down into two categories.

Side effect Description and what to do
Things to tell your doctor immediately
Allergic reactions Skin rash, itching, swelling of the face, lips or tongue.
Difficulty breathing Cough, chest pain, difficulty breathing.
Digestive system problems Severe stomach pain, diarrhea, blood in the stool, or black stool.
Liver problems Yellowing of the eyes or skin, dark urine, pain in the upper right side of the stomach, nausea.
Kidney problems Decreased urine output or difficulty urinating.
Increased blood sugar levels Intense thirst, dry mouth, frequent urination, and fruity breath odor.
Other serious symptoms Severe headache, vision changes, joint pain, muscle weakness, numbness in the limbs, fever, swollen lymph nodes.
Usually not serious (but tell your doctor if it persists)
Tiredness The usual tiredness.
Appetite Decreased desire to eat.
Hair loss Hair loss.

What else should I pay attention to when taking this medicine?

Your doctor will monitor your condition closely throughout your treatment. You will also need to have regular blood tests (blood work) to see how the medicine is affecting your body.

This is very important: You should completely avoid getting pregnant while taking this medicine and for 4 months after stopping treatment. Also, avoid breastfeeding during this time. This can seriously harm the baby in the womb. So talk to your doctor about this.

Finally, this medicine is for you only. Never share it with anyone else.

💡 Take-Home Message

  • Pembrolizumab is a modern drug that stimulates our body's own immune system to attack cancer cells.
  • Before starting treatment, it is essential to tell your doctor your complete health history, especially about other illnesses, allergies, and pregnancy.
  • This medicine is given through a vein in a hospital. It is very important to receive treatment on time.
  • It is very important to avoid pregnancy and breastfeeding completely during and for 4 months after treatment.
  • If you experience any serious side effects such as difficulty breathing, severe diarrhea, or yellowing of the skin, inform your doctor immediately.
  • You are not on this journey alone. Your doctor and medical team are with you. Don't hesitate to talk to them about any questions or concerns you may have.
❓ FAQ

FAQ

Evidence-based clinical answers to common patient questions

What if I take too much medicine?

This is a hospital-based drug, so the chances of this happening are low. However, if you think you have taken too much of this medicine, go to a hospital's Emergency Unit (ETU) immediately . Or call the National Poisons Information Centre at the Colombo National Hospital for advice.

What if I miss a treatment session?

It is very important to take this medicine on the scheduled date and time. If you are unable to go to the hospital on the scheduled date, call your doctor immediately and let them know so they can advise you on what to do next.

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⚠️ Important: Medical articles and information on Nirogi Lanka are strictly for educational and awareness purposes and do not substitute professional medical advice, diagnosis, or treatment. Always consult a qualified physician for any medical concerns.