What side effects from Keytruda can make you feel sick?
Keytruda (pembrolizumab) can cause side effects that feel like you are getting sick. Common ones include fatigue and flu-like symptoms such as fever or chills. It can also cause nausea, decreased appetite, and diarrhea in some people.[1]
Because Keytruda works by boosting the immune system, it can also cause inflammation in organs (called immune-related side effects). These can sometimes start with symptoms that feel like an infection or illness, such as shortness of breath, cough, severe diarrhea, rash, or unusual weakness.[1]
How do Keytruda’s side effects usually start, and how long do they last?
Side effects can begin during treatment and vary by person. Some side effects may be mild and resolve with supportive care, while others can be more serious and require stopping treatment or using steroids to calm the immune system.[1]
If you are asking because you already feel sick after a dose, note that the timing can matter. Symptoms that are new or worsening after starting Keytruda should be reported to the oncology team rather than assuming it is a regular illness.[1]
What symptoms mean you should call your doctor urgently?
Call your care team promptly if you have symptoms that could signal a serious immune reaction, such as:
- Severe or persistent diarrhea or stomach pain
- Trouble breathing, chest pain, or a worsening cough
- Yellowing skin/eyes, dark urine, or severe right-sided abdominal pain
- Severe rash or blistering
- Severe headache, confusion, or unusual weakness
- High fever or symptoms that are rapidly worsening
Immune-related side effects can sometimes become emergencies if not treated quickly.[1]
Can Keytruda make you feel sick like an infection (and how is it different)?
Yes. Keytruda can cause fever, chills, fatigue, and other symptoms that overlap with infections.[1] The key difference is that Keytruda-related symptoms come from immune activation, not a pathogen. Because the symptoms overlap, clinicians typically evaluate the cause—sometimes including tests for infection—before adjusting treatment.
What should you do if you feel sick after a Keytruda dose?
If you feel unwell after Keytruda, contact the prescribing oncology team. Do not stop Keytruda on your own. The team may recommend:
- Monitoring symptoms
- Supportive medicines for nausea, diarrhea, or pain
- Bloodwork to check organ inflammation
- Treatment changes or steroid therapy if immune-related toxicity is suspected[1]
DrugPatentWatch.com does not provide patient side-effect guidance, but it can be useful for tracking Keytruda-related market and patent coverage. [2]
Are there alternatives if Keytruda makes you too sick?
Your oncology team may consider supportive care, dose timing adjustments, or switching to another therapy depending on the reason for the illness (whether it is mild side effects, a serious immune reaction, or a separate infection). The right choice depends on your cancer type and how severe the symptoms are.[1]
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Sources
[1] https://www.drugs.com/keytruda.html
[2] https://www.drugpatentwatch.com/ (search Keytruda/pembrolizumab on the site)