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Keytruda (pembrolizumab)

Keytruda® is an immunotherapy that is a monoclonal antibody. Antibodies are a normal part of the immune system that attach to antigens (such as germs) to mark them for destruction by the immune system. Monoclonal antibodies are created in a laboratory to attach to specific antigens on the surface of cancer cells. Pembrolizumab targets the PD-1 receptor and the interaction with the molecules which bind to the receptor, PD-L1 and PD-L2. Some cancer cells affect the PD-1 pathway. When this pathway is affected by the cancer cells, the cancer can grow and spread without being kept in check by the T-cells and the immune system. By blocking the PD-1 pathway, pembrolizumab can help the body’s T-cells and immune system fight the cancer.1,2

Pembrolizumab is approved for multiple first-line treatment options for patients with advanced non-small cell lung cancer. It can be used along with chemotherapy for metastatic nonsquamous NSCLC with no abnormal EGFR or ALK gene. As well as first-line treatment in combination with chemotherapy for metastatic squamous NSCLC.4 It can also be used as a single medication for certain forms of advanced or metastatic NSCLC. Pembrolizumab is used to treat other types of cancer, such as some melanoma cancers and some squamous cell carcinoma cancers.1,2

Pembrolizumab is also approved as a first-line treatment for stage III (who are not candidates for chemoradiation or surgical resection) or metastatic non-small cell lung cancer patients, with a PD-L1 TPS ≥ 1% and no abnormal EGFR or ALK gene. Biomarker testing (also called molecular testing) is done on a biopsy sample of the tumor to check if PD-L1 is present. Additionally, pembrolizumab is approved for the treatment of metastatic small cell lung cancer (SCLC) who have had cancer progression after, or while taking, platinum-based chemotherapy and is intended for those who have previously tried at least one other treatment option.

Receiving pembrolizumab

Pembrolizumab is given as an infusion that is administered through an IV (intravenous) line over 30 minutes. It is usually given once every three weeks. Patients may be given medications before the infusion to reduce the chance of allergic reactions to pembrolizumab. The dosage of pembrolizumab is determined based on the type of cancer, and may take into account a patient’s weight.2

Side effects of pembrolizumab

Pembrolizumab may cause side effects, and in some cases, these side effects can be severe. Any side effects should be reported to a health care professional. Side effects experienced in greater than 30% of patients recieving pembrolizumab include low red blood cells (anemia), fatigue, hyperglycemia (high levels of sugar in the blood), hyponatremia (a decreased level of sodium in the blood), hypoalbuminemia (a decreased level of albumin in the blood), itching, cough, and nausea. Less common side effects experienced in 10-29% of patients receiving Keytruda include rash, decreased appetite, hypertriglyceridemia (an increased level of fatty acids in the blood), constipation, diarrhea, joint pain (arthralgia), pain in arms and legs, shortness of breath, swelling, headache, vomiting, chills, muscle pain (myalgia), insomnia (difficulty sleeping), abdominal pain, back pain, fever, vitiligo (a skin disorder with patchy loss of color), dizziness, and upper respiratory tract infection. Rarely, pembrolizumab can cause the severe side effect of an immune-mediated reaction. This can affect the bowels, liver, skin, nerves and the endocrine system. Patients will be monitored for symptoms of this reaction (diarrhea, rash, and neuropathy) and blood work may be checked for elevated liver enzymes and thyroid function.2,3


Patients receiving pembrolizumab should talk to their doctor about other medications, herbal remedies, and any supplements they are taking, as well as any other health conditions. Patients should talk to their doctor before receiving immunizations or vaccinations while taking Keytruda to make sure they are appropriate. Patients who are pregnant or may become pregnant during treatment should discuss their condition with their doctor before starting pembrolizumab, as it may be hazardous to the fetus. It is not recommended for men or women to conceive a child while taking Keytruda, and patients are advised to use contraception, such as condoms. It is not known whether pembrolizumab passes into breast milk, and patients should not breastfeed while taking pembrolizumab.2

Written by: Emily Downward | Last reviewed: January 2020.
  1. Keytruda product website, Merck & Co, Inc. Accessed online on 9/29/16 at
  2. Chemocare. Accessed online on 9/27/16 at
  3. Taber’s online medical dictionary. Accessed online on 9/29/16 at
  4. FDA approves pembrolizumab in combination with chemotherapy for first-line treatment of metastatic squamous NSCLC. Access online 10/31/2018.