What side effects of keytruda need urgent medical attention?

Keytruda Side Effects Requiring Urgent Medical Attention

Keytruda (pembrolizumab), an immunotherapy for cancers like melanoma and lung cancer, can trigger immune-related adverse reactions where the immune system attacks healthy tissues. These often need immediate medical care to prevent severe outcomes like organ damage. Always contact your doctor or seek emergency help for new or worsening symptoms during treatment.[1]

Immune-Mediated Reactions Demanding Quick Action

• Infusion reactions: Fever, chills, rash, itching, low blood pressure, or breathing trouble during or shortly after infusion. Stop and call 911 if severe.[1][2]
  
• Severe allergic reactions (anaphylaxis): Swelling of face/lips/tongue, throat tightening, trouble breathing, rapid heartbeat, or dizziness. This is a medical emergency.[1]
  
• Pneumonitis (lung inflammation): New or worsening cough, shortness of breath, chest pain. Can progress rapidly; urgent imaging and steroids often required.[1][3]
  
  

Organ-Specific Urgent Issues

• Colitis or diarrhea: Severe (8+ stools/day), bloody stools, or abdominal pain. Leads to dehydration or perforation; may need hospitalization.[1][2]
  
• Hepatitis (liver inflammation): Yellowing skin/eyes (jaundice), dark urine, severe fatigue, or right upper stomach pain. Liver enzymes can spike dangerously.[1]
  
• Endocrinopathies: Sudden symptoms like extreme fatigue, weight changes, low blood pressure (adrenal crisis), rapid heartbeat (thyroid storm), or vision changes (pituitary issues). Check blood sugar/thyroid urgently.[1][3]
  
• Nephritis (kidney damage): Reduced urine output, swelling in legs, blood in urine, or high blood pressure. Kidney function tests critical.[1]
  
• Myocarditis or neurological effects: Chest pain, irregular heartbeat, confusion, seizures, weakness, or vision loss. Heart or brain involvement can be life-threatening.[1][2]
  
  

Skin and Other Severe Reactions

• Severe skin reactions: Stevens-Johnson syndrome or toxic epidermal necrolysis signs like painful red/purple rash, blisters, peeling skin, or mouth sores. Seek ER care immediately.[1]
  
• Encephalitis or Guillain-Barré: Headache, fever, stiff neck, muscle weakness, numbness, or paralysis starting in legs. Rare but requires urgent neurology input.[3]
  
  Patients on Keytruda should carry an alert card listing these risks. Incidence varies: severe immune reactions hit 10-20% in trials, higher with combination therapies.[2] Report to FDA MedWatch if symptoms occur.[1]
  
  Sources
  [1]: Keytruda Prescribing Information (Merck)
  [2]: FDA Label for Pembrolizumab
  [3]: NCCN Guidelines: Management of Immunotherapy Toxicity