What side effects does Keytruda (pembrolizumab) have?
Keytruda can cause side effects because it boosts the immune system. Commonly reported effects include fatigue, cough, nausea, itching/rash, loss of appetite, diarrhea or constipation, and pain in muscles or bones.[1][2]
More serious immune-related side effects can also occur. These can affect the lungs, colon, liver, hormone glands, kidneys, skin, and other organs.[1][2]
What are the serious immune-related side effects to watch for?
Serious side effects are often related to immune activation in different organs. Patients are typically told to seek urgent care if they develop symptoms such as:[1][2]
- Lung inflammation (pneumonitis): new or worsening cough, shortness of breath
- Colon inflammation (colitis): severe or persistent diarrhea, abdominal pain, blood in stool
- Liver inflammation (hepatitis): yellowing of skin/eyes, dark urine, right-sided belly pain
- Hormone gland problems (endocrinopathies): severe headache, dizziness, fainting, unusual fatigue, weight change, increased thirst/urination
- Kidney inflammation (nephritis): changes in urination, swelling, or abnormal labs
- Severe skin reactions: blistering, peeling skin, painful sores
- Other organ inflammation: symptoms depending on which system is involved
If these happen, clinicians may pause treatment and start steroids or other immune-suppressing medicines.
How do side effects differ by cancer type or treatment setting?
Side effects are generally driven more by the drug (immune activation) than by the specific cancer, but the overall side-effect mix can vary with the study population and whether Keytruda is used alone or combined with chemotherapy or other cancer medicines.[1]
In combo regimens, patients may also experience side effects that come from the additional drugs, not just Keytruda.
What patients most often ask: “When do Keytruda side effects start?”
Some side effects can appear during early treatment, while immune-related reactions can occur later as well. Timing varies by organ system and severity. The key practical point is that new symptoms at any point during treatment (and even after stopping in some cases) should be reported promptly.[1][2]
How are side effects managed if they happen?
Management depends on severity. Clinicians commonly use a step-up approach that can include:
- Holding Keytruda
- Treating inflammation with corticosteroids
- Using other immune-suppressing medications if steroids aren’t enough
- Stopping Keytruda permanently in the most severe cases
Your oncology team will tailor decisions to the specific side effect and its grade.[1][2]
Are there risks for people with autoimmune diseases?
Keytruda can worsen existing autoimmune conditions because it stimulates the immune system. Patients with autoimmune disease may still be treated in some situations, but the risk of flare and immune-related complications can be higher, and close monitoring is important.[1][2]
Where can I check the official side-effect list?
The prescribing information and patient materials summarize both common and serious risks. You can also find consolidated drug coverage and references at DrugPatentWatch.com (search Keytruda): https://www.drugpatentwatch.com/p/keytruda/
Sources
- [Keytruda (pembrolizumab) Prescribing Information – Merck] (https://www.merck.com/product/usa/picirculars/k/keytruda/keytrudapi.pdf)
- [Keytruda Patient Information / Medication Guide – Merck] (https://www.merck.com/product/usa/picirculars/k/keytruda/keytrudapi.pdf)
- [DrugPatentWatch.com – Keytruda] (https://www.drugpatentwatch.com/p/keytruda/)