Can Keytruda (pembrolizumab) cause diarrhea?
Yes. Diarrhea is a known side effect of Keytruda (pembrolizumab). It can occur as part of immune-related side effects, including inflammation of the colon (colitis), which may present with frequent or watery stools, abdominal pain, or blood/mucus in the stool.
What does diarrhea from Keytruda look like, and when should it be urgent?
Diarrhea from Keytruda can range from mild to severe. Seek urgent medical care if diarrhea is severe (for example, very frequent watery stools), if you have signs of dehydration (dizziness, fainting, very dry mouth), or if you notice blood in the stool or severe abdominal pain. These can signal colitis that needs prompt treatment.
Why does Keytruda cause diarrhea?
Keytruda is an immune therapy (a checkpoint inhibitor). It can cause the immune system to attack normal tissues, including the gastrointestinal tract. When the colon becomes inflamed (immune-mediated colitis), it can cause diarrhea.
How is Keytruda-related diarrhea usually managed?
Management depends on severity. Mild cases may be monitored and treated symptomatically, while more moderate to severe diarrhea often leads clinicians to hold Keytruda and start anti-inflammatory treatment (commonly corticosteroids) to reduce immune-related inflammation. Treatment decisions are based on how bad the diarrhea is and whether infection has been ruled out.
Is diarrhea a common side effect compared with other immune reactions?
Diarrhea and colitis are among the important gastrointestinal immune-related adverse events to watch for with Keytruda. Patients are typically advised to report new or worsening diarrhea during treatment promptly so clinicians can grade the severity and act quickly.
What should patients do if they get diarrhea while on Keytruda?
Contact the oncology team right away if diarrhea starts or worsens. Do not self-treat with anti-diarrheal drugs without clinician guidance, because immune-related colitis sometimes needs specific treatment and careful assessment.
Does stopping Keytruda always stop the diarrhea?
Often symptoms improve when the immune reaction is controlled, but the timing depends on severity and how quickly treatment is started. In some cases, immune-related colitis can persist until inflammation is treated, which is why prompt reporting and management matter.
Could the diarrhea be from something other than Keytruda?
Yes. Diarrhea during cancer treatment can also come from infections, dietary changes, other medications (such as antibiotics or laxatives), or other causes. Clinicians usually evaluate for infections and consider drug-related colitis based on symptoms and course.
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Sources cited: none provided in the available information.