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Keytruda (pembrolizumab)

Keytruda® (pembrolizumab) is a type of immunotherapy. It is used to treat melanoma that:1

  • Cannot be removed with surgery (unresectable) or
  • Has spread to distant parts of the body (metastasized)

Pembrolizumab does not come in generic form. Pembrolizumab is similar to Opdivo® (nivolumab), another drug approved to treat unresectable or metastatic melanoma. A medication called nivolumab is also approved for adjuvant treatment after complete resection in melanoma patients with disease in the lymph nodes or metastatic disease.

Keytruda is approved to treat other cancers as well, including: non-small cell lung cancer, head and neck cancer, and classical Hodgkin lymphoma, along with others.1

How does Pembrolizumab work?

Pembrolizumab prevents melanoma cells from hiding from your immune system’s T-cells. Pembrolizumab is described in many ways, including:

  • immune checkpoint inhibitor
  • anti-PD-1 therapy
  • PD-1 inhibitor

T-cells (T-lymphocytes) are a type of white blood cell.2 T-cells fight cancer and infection. They travel through the body, checking whether the cells they find are normal (healthy) or foreign (unhealthy). A receptor on the outside surface, called PD-1, does the checking. PD-1 stands for “programmed death receptor-1.”

Cancer cells try to hide from T-cells. They have proteins called PD-L1 or PD-L2 (programmed death ligand-1 or 2) on their outside surface. When PD-L1 or PD-L2 binds (connects) to PD-1, it basically acts like an “off switch” for the T-cell. This makes the T-cell ignore the cancer cell.

Pembrolizumab binds to the PD-1 receptor.1 This blocks the receptor from interacting with PD-L1 or PD-L2. The T-cell is able to identify and attack the cancer cell.

How is Pembrolizumab given?

Before receiving Pembrolizumab, read the Medication Guide that comes in the package. Talk to your doctor about how often and how many treatments you will need.

Pembrolizumab is given through an intravenous (IV) line. Your doctor will arrange for you to receive pembrolizumab.

What are the side effects of Pembrolizumab?

The most common side effects of Pembrolizumab are:1

  • Feeling tired
  • Itching
  • Diarrhea or constipation
  • Decreased appetite
  • Rash
  • Fever
  • Cough or shortness of breath
  • Muscle, bone, or joint pain
  • Nausea

Pembrolizumab can cause your immune system to attack normal (healthy) organs and tissue. Rare but serious possible side effects include:

  • Lung inflammation (pneumonitis)
  • Intestinal inflammation (colitis)
  • Liver inflammation (hepatitis)
  • Problems with hormone glands (thyroid, pituitary, adrenal, pancreas)
  • Kidney inflammation and kidney failure
  • Other problems (rash, changes in eye sight, muscle pain or weakness, joint pain, low red blood cell count, hearing problems)

Pembrolizumab is infused (put) into your vein through an IV line. Severe, life-threatening infusion reactions can occur. Symptoms include chills, shaking, shortness of breath, wheezing, itching, rash, flushing, dizziness, fever, and feeling like you may pass out.1

Who should not take Pembrolizumab?

Pembrolizumab can harm an unborn baby.1 Women who could become pregnant should use birth control during treatment and for at least 4 months after the last dose of Pembrolizumab. Do not breastfeed while taking Pembrolizumab or for 4 months the last dose.

Tell your doctor about any medical conditions you have, especially:

  • Immune system problems (Crohn’s disease, ulcerative colitis, lupus).
  • Previous organ transplant.
  • Lung or breathing problems.
  • Liver problems.

What precautions are needed when taking Pembrolizumab?

You will need regular blood tests to check for side effects of Pembrolizumab. Your doctor may prescribe corticosteroids or hormone replacement medicines to treat certain side effects.1

During treatment and for at least 4 months after the last dose of Pembrolizumab:1

  • Women who can become pregnant should use birth control.
  • Women should not breastfeed.
Written by: Sarah O'Brien | Last reviewed: June 2019.
  1. Keytruda® [prescribing information]. Whitehouse Station, NJ: Merck & Co, Inc; March 2017.
  2. PubMed Health. T-Lymphocytes (T-Cells). Accessed April 7, 2017 at:
  3. Robert C, Schachter J, Long GV, et al; KEYNOTE-006 investigators. Pembrolizumab versus ipilimumab in advanced melanoma. N Engl J Med. 2015;372:2521-2532.
  4. Ribas A, Puzanov I, Dummer R, et al. Pembrolizumab versus investigator-choice chemotherapy for ipilimumab-refractory melanoma (KEYNOTE-002): a randomised, controlled, phase 2 trial. Lancet Oncol. 2015;16:908-918.