What to Know About Keytruda (Pembrolizumab)

An Immunotherapy Drug Used to Treat Certain Cancers.

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Keytruda (pembrolizumab) is an immunotherapy drug used to treat several types of cancer. It is given to patients as an infusion, which means that the medication goes into a vein slowly over a specified period of time. Most people taking Keytruda to treat cancer will need to have infusions every few weeks.

While it is a treatment for cancer, Keytruda is not the same as chemotherapy or radiation. The drug is made from humanized antibodies that are specifically designed to release the brake put by the cancer cells on the immune system. When someone has cancer, these antibodies help their body's immune system fight cancer cells.

Like many treatments for cancer, Keytruda does have side effects that people taking it will want to know about. There are also some people who should not take Keytruda.

Immunotherapy infusion for cancer patients
 Ulrika / iStock / Getty Images 


If you have certain cancers, your healthcare provider may want you to receive Keytruda. The drug contains a special type of protein (antibody) that can be made by scientists in a lab. These proteins, called monoclonal antibodies (mAbs), can help the body fight cancer cells.

There are different kinds of mAbs. Keytruda is what is sometimes called a targeted therapy for cancer.

Some mAbs are created to go after specific proteins (antigens) found on cancer cells and destroy them. Others, like Keytruda, are designed to specifically inhibit interactions between cancer cells and the immune cells through which cancer cells put a brake on the immune cells.

The goal of targeted therapy is to make sure the body's immune system only attacks cancer cells and does not damage healthy cells.

Keytruda works to block a specific receptor on cells that regulate the body's immune response called PD-1. The main job of PD-1 is to keep the immune system from attacking cells in the body. Usually, this is a good thing, but when there are cancer cells in the body, the immune system needs to be able to attack and destroy them.

When someone receives Keytruda, it blocks PD-1 and allows the person's immune system to attack and destroy cancer cells.

Keytruda can be used alone or with other medications to treat several cancers. Your healthcare provider will need to evaluate your overall health and the specifics of your cancer (such as stage and type) to determine if the treatment is appropriate for you.

You may be prescribed Keytruda if you have:

Researchers are also studying other kinds of cancer (including certain colorectal tumors) to see if Keytruda might be a good option for treatment.

Off-Label Uses

In some cases, a healthcare provider will have a patient take a medication that isn't typically used to treat their disease or condition. This is called off-label use.

Your healthcare provider might prescribe Keytruda off-label in certain circumstances (for example, if your other treatments are not working well or you are taking part in a clinical trial).

In some cases, your healthcare provider might recommend that you receive a different dose of Keytruda or have your infusions on a different schedule than what is usually prescribed.

Before Taking

If your healthcare provider is considering having you take Keytruda, you may need to have some tests done before the medication can be prescribed. These tests are used to find out more about the type of cancer you have, as well as your overall state of health. This information helps your medical team put together the best possible treatment plan for you.

Some of the routine tests your healthcare provider may order include:

You may need to have these tests repeated while you are taking Keytruda. Doing so allows your healthcare provider to monitor your body's response as it adjusts to treatment and ensure it's safe for you to continue receiving Keytruda.

Biomarker Tests

Your healthcare provider might want you to have a special test that can help them learn more about the type of cancer you have been diagnosed with.

A biomarker test is used to look closely at the cells that make up the tumor you have. This information can help healthcare providers predict how well your body will respond to different types of cancer treatment.

Before prescribing Keytruda, your healthcare provider might have you tested for the following biomarkers:

  • PD-L1: Can be found in tumors in all tumors for which Keytruda is currently indicated.
  • MSI-H/dMMR: Can be found in tumors in certain advanced cancers

Your healthcare provider will use the information about your cancer and state of health to determine whether you should take Keytruda, as well as the dose and schedule of your treatment.

Cancer Typing and Staging

The type and stage of your cancer will influence your healthcare provider's decision about treatment. These recommendations may also change over time as your cancer progresses or improves.

For example, Keytruda is part of the first-line treatment for patients with advanced renal cell carcinoma. On the other hand, if you have metastatic small cell lung cancer, your healthcare provider might want you to try other treatments before they prescribe Keytruda.

Precautions and Contraindications

You will need to have an appointment (or more than one) with your healthcare provider and other members of your cancer care team before you begin treatment. In addition to ordering tests, your healthcare providers will perform exams and ask you questions about your health.

Other Health Conditions

It's important that your healthcare provider knows about any other health conditions you have. People who have certain medical conditions may be more likely to have side effects from Keytrud, or the drug might not work as well.

Medications and Supplements

You'll also need to tell them about all the medications you take—including over-the-counter medications, vitamins, supplements, and alternative remedies. You may need to stop taking certain medications or change your dose while you are receiving Keytruda.


Keytruda and immunizations both affect how your immune system works. While healthcare providers typically recommend that their patients receive immunizations, such as the annual influenza vaccine or a tetanus booster, you may not be able to have these vaccines while you are being treated. Your healthcare provider will let you know which, if any, immunizations you can receive during your treatment.

Pregnancy and Breastfeeding

It's not safe to get pregnant or try to conceive while you are taking Keytruda. If you are capable of becoming pregnant or impregnating someone, you'll need to discuss fertility and birth control options with your healthcare provider before you start treatment.

It's not known if Keytruda passes into breast milk. Therefore, it is recommended that patients do not breastfeed while they are being treated with the medication. Most patients are asked to wait an additional four months after they stop treatment to start breastfeeding.


Keytruda can be given by itself or with other cancer treatments (adjuvant therapy). How much Keytruda you receive as well as how often you receive it will depend on several factors.

Your healthcare provider will consider the type and stage of your cancer, other health conditions you have, the medications you are taking, your age, how much you weigh, and other factors to determine your dose of Keytruda.


If you are allergic to certain medications or ingredients, you may be given some medicine before you receive your infusion of Keytruda to help prevent side effects or an allergic reaction.

Depending on how you respond to treatment, your healthcare provider might change the dose of Keytruda you receive, or increase or decrease the number of infusions you get over the course of your treatment.

If you need to start or stop taking other medications (especially those that affect your immune system, like corticosteroids) or develop other health conditions while you are taking Keytruda, your healthcare provider can adjust your dose and treatment schedule if necessary.

If you are receiving other therapies for cancer, such as radiation and chemotherapy, your healthcare provider may make changes to your Keytruda dose or schedule as part of your overall treatment plan.

How to Take and Store

Patients typically receive Keytruda every three weeks. Recently, it has also been approve d for use every six weeks. The medication is slowly infused into a vein in their arm through an IV (usually over the course of 30 minutes).

You will need to go to the hospital, your healthcare provider's office, a cancer care center, or an infusion clinic to receive your treatment. You will not need to store or prepare the medication at home.

The length of time you will have to get infusions will depend on the specifics of your cancer and how it responds to Keytruda. Unless there are complications, patients usually receive treatment for up to 24 months.

Side Effects

As with any medication or treatment, Keytruda can have side effects. Most are mild and won't require a person to stop receiving treatment. However, in some cases, the adverse effects can serious or even life-threatening.

Your healthcare provider will explain the possible side effects before prescribing you Keytruda. They may ask you to keep track of any symptoms you have while you are receiving treatment.

Your healthcare provider will also go over the signs of serious reactions to look for, as well as give you instructions on what to do if they occur (for example, calling the office or going to your local emergency room).

While the list of side effects might seem daunting, keep in mind that most people being treated with Keytruda don't experience every single one. Many patients only experience mild discomfort that gradually gets better as their body adjusts to the treatment.


There are some mild side effects that people being treated with Keytruda frequently report (experienced by more than 30% of patients ), including:

Around 10% to 20% of patients taking Keytruda report experiencing:

  • Rashes
  • Reduced appetite
  • Elevated levels of triglycerides in the blood (hypertriglyceridemia)
  • Elevated levels of liver enzymes
  • Low calcium levels (hypocalcemia)
  • Bowel changes (constipation/diarrhea)
  • Pain in arms and legs
  • Shortness of breath
  • Swelling
  • Headache
  • Vomiting
  • Chills
  • Muscle and joint pain
  • Trouble sleeping (insomnia)
  • Belly (abdominal) pain
  • Back pain
  • Fever
  • Vitiligo
  • Dizziness
  • Upper respiratory tract infection

Children who are being treated with Keytruda are more likely than adults to experience certain side effects, including fatigue, stomachaches, and throwing up. Kids also appear to be more likely to have elevated liver enzymes and low sodium levels during treatment.


Keytruda also carries the risk of severe side effects and adverse reactions for some people who receive it. In some cases, these side effects may be life-threatening.

Seek immediate medical care if you experience any of the following symptoms while you are being treated with Keytruda:

  • A fever of 100.4 F (38 C) or higher
  • Signs of an allergic reaction (wheezing, chest tightness, itching, a bad cough, facial swelling or swelling of your mouth, lips, tongue, and throat)
  • A racing heart or pulse
  • Rapidly gaining or losing weight
  • A cough that you didn't have before or that is getting worse
  • Chest pain or having trouble breathing
  • Severe abdominal pain (especially if it feels worse on the right side of your belly) that is accompanied by diarrhea
  • Dark-colored stool or stool that has blood in it
  • Yellow color to the white part of your eyes or your skin (jaundice)
  • A headache that doesn't go away or is not like headaches you typically get
  • Feeling extremely weak
  • Confusion or disorientation
  • Memory problems
  • Getting dizzy and passing out/fainting (syncope)
  • Eyesight changes
  • Seizures

If you experience any serious symptoms while you are taking Keytruda, call your healthcare provider right away or visit your local emergency room.

While they don't necessarily mean you're having a serious adverse reaction, tell your healthcare provider if you experience any of the following while taking Keytruda. They will need to determine if your symptoms are related to your treatment:

  • You do not feel like eating and drinking and have not done so for 24 hours.
  • You feel sick to your stomach and medication does not make it better, Or you throw up more than four or five times in 24 hours.
  • You are dehydrated (feeling tired, dizzy, thirsty, have a dry mouth, dark "tea-colored" urine or you are not peeing as much as you usually do).
  • You are feeling more hungry and eating more than usual, which may lead to weight gain.
  • You have a rash on your skin (may or may not be itchy), develop skin sores (anywhere on your body including near your genitals), or your skin starts peeling.
  • Your hands and feet feel numb or "tingly".
  • Your lymph nodes (such as those in your neck, underarm, and groin) feel swollen or are tender and painful.
  • You feel cold all the time.
  • Your hair is thinning or falling out.
  • You notice that you are bleeding or bruising easily.

Patients who are receiving Keytruda may also need to have other cancer therapies at the same time. If your treatment requires more than one drug, your healthcare provider will let you know about additional symptoms, side effects, and risks associated with your treatment that you need to be aware of.

Warnings and Interactions

There are some specific warnings and interactions you should know about if you are prescribed Keytruda. It's important that you discuss these risks with your healthcare provider and make sure that you thoroughly understand what they mean before you start treatment.

Immune-Mediated Reactions

People who are taking drugs that affect their immune system (including Keytruda) are at risk for a specific kind of complication called an immune-mediated response.

Since Keytruda makes changes to a person's immune system (which is involved in many whole-body processes), the symptoms or complications they experience can stem from nearly any body system, including the heart and lungs, digestive tract, and kidneys.

Keytruda can also affect the organs that regulate hormone levels, including the thyroid, adrenal glands, and pancreas.

Make sure your healthcare provider knows if you have any issues with your immune system. If you have an autoimmune disease (such as lupus or ulcerative colitis), have a compromised immune system because of a disease like HIV/AIDS, or you have had an organ transplant, you may be more at risk for immune-mediated reactions.

It's also possible that treatment with Keytruda could make these problems worse or cause new problems related to your body's immune function.

A Word From Verywell

If you have cancer, your healthcare provider might talk to you about treatment with Keytruda. The treatment is not appropriate for every type of cancer or every patient who has cancer, but it might be a good option for you.

Keytruda is different from other cancer treatments (such as chemotherapy and radiation). It uses antibodies made in a lab that help the body's immune system attack cancer cells.

Your healthcare provider will decide on the right dose for you. Most patients will have infusions of their dose of Keytruda every three weeks for up to 24 months.

If you have certain medical conditions, especially those that affect your immune system, you may not be able to take Keytruda. Your healthcare provider might prescribe it but will carefully monitor your dose and schedule to ensure it's safe for you to continue receiving treatment.

Most side effects of Keytruda are mild and will get better as your body adjusts, but there are some serious side effects you should know about. If you have problems with your immune system or have had an organ transplant, you might be more at risk for them.

Children who are taking Keytruda are sometimes more likely to have particular side effects compared to adults who are being treated with it.

If you have any risk factors for serious side effects or complications related to taking Keytruda, or you develop other health conditions or need to take other medications while you are being treated, your healthcare provider can adjust or stop your dose.

During your treatment with Keytruda, your healthcare provider might ask you to keep track of how you are feeling, including and symptoms you have that could be related to the medication.

While it's not common to develop serious complications if you are not at risk, if you experience severe side effects, call your healthcare provider immediately or go to your local emergency room.

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11 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. NCI Dictionary of Cancer Terms. Keytruda. National Cancer Institute.

  2. Cleveland Clinic Cancer. Keytruda (pembrolizumab) chemotherapy drug information. Chemocare.com.

  3. The American Cancer Society medical and editorial content team. Monoclonal antibodies and their side effects. American Cancer Society.

  4. NCI Dictionary of Cancer Terms. PD-1. National Cancer Institute.

  5. Office of the Commissioner. Understanding unapproved use of approved drugs “off kabel. U.S. Food and Drug Administration.

  6. KEYTRUDA® (pembrolizumab). Keytruda frequently asked questions. Merck & Co., Inc.

  7. Food and Drug Administration (FDA). Medication guide KEYTRUDA ® for injection.

  8. Merck & Co., Inc. KEYTRUDA® (pembrolizumab). Health care professional guidelines and indications.

  9. KEYTRUDA® (pembrolizumab). Dosing and administration with KEYTRUDA® (pembrolizumab). Merck & Co., Inc.

  10. Schoen H. Keytruda: Highlights of prescribing information. Merck & Co., Inc.

  11. KEYTRUDA® (pembrolizumab). Side effects. Merck & Co., Inc.

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