Keytruda is a prescription medicine used to treat several types of cancer, including melanoma, non-small cell lung cancer, head and neck squamous cell cancer, classical Hodgkin lymphoma, urothelial carcinoma, microsatellite instability-high cancer, gastric cancer, cervical cancer, and primary mediastinal large B-cell lymphoma [1].

As with any medication, Keytruda may cause side effects. Some common side effects of Keytruda include fatigue, cough, nausea, rash, decreased appetite, constipation, joint pain, and diarrhea. These side effects are usually mild to moderate in severity and can be managed with medication or other supportive care measures [2].

However, Keytruda can also cause more serious side effects, including immune-mediated side effects. These side effects occur when the immune system attacks healthy cells in the body, which can lead to inflammation and damage to organs and tissues. Immune-mediated side effects can affect many different parts of the body, including the lungs, liver, kidneys, intestines, and endocrine system [3].

Some of the most common immune-mediated side effects of Keytruda include pneumonitis (inflammation of the lungs), colitis (inflammation of the colon), hepatitis (inflammation of the liver), hypothyroidism (underactive thyroid gland), hyperthyroidism (overactive thyroid gland), and adrenal insufficiency (insufficient production of hormones by the adrenal glands) [2].

Other potential side effects of Keytruda include infusion reactions (allergic reactions that occur during or shortly after receiving the medication), skin reactions (such as Stevens-Johnson syndrome or toxic epidermal necrolysis), and embryofetal toxicity (harm to a developing fetus if used during pregnancy) [1, 2].

It is important to note that not all patients will experience side effects from Keytruda, and the severity and duration of side effects can vary from person to person. Patients receiving Keytruda should be closely monitored for any signs of side effects, and should contact their healthcare provider immediately if they experience any new or worsening symptoms [3].

Sources:
[1] Drug Patent Watch. Keytruda. Retrieved from https://www.drugpatentwatch.com/p/biologics/tradename/KEYTRUDA
[2] Keytruda. Side Effects. Retrieved from https://www.keytruda.com/side-effects/
[3] Cancer.net. Side Effects of Immunotherapy. Retrieved from https://www.cancer.net/navigating-cancer-care/how-cancer-treated/immunotherapy-and-vaccines/side-effects-immunotherapy