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Pembrolizumab, more commonly known as KEYTRUDA, is an immunotherapy drug used to treat various types of cancer that has had promising results in many patients. Despite this, it's essential to be aware of potential short and long-term side effects.

What Are the KEYTRUDA Side Effects?

Common side effects experienced by patients taking KEYTRUDA include nausea, skin dryness or rashes, breathlessness, low thyroid levels (hypothyroidism), and decreased appetite.

In addition to these common KEYTRUDA side effects, some patients may experience more severe reactions to treatment. Some of the commonly reported mild side effects include:

  • Fatigue
  • Muscle pain
  • Decreased appetite and weight loss
  • Pruritus (itching)
  • Diarrhea
  • Nausea
  • Severe skin reactions
  • Increased sweating
  • Hair loss

Your doctor will monitor your health closely while you're undergoing immunotherapy with KEYTRUDA and may adjust your dosage or discontinue treatment if you experience severe side effects. 

How Effective is KEYTRUDA?

It works by stimulating the immune system to attack and destroy cancer cells more effectively. The effectiveness of this immunotherapy drug can be measured by comparing its success rate with traditional chemotherapy treatments.

In a clinical trial involving patients with non-small cell lung cancer (NSCLC), it was found that half of the patients on chemotherapy were alive at 3.3 months without their cancer spreading, growing, or getting worse compared to just 2.1 months for those treated with KEYTRUDA. This indicates that while both treatment options have their benefits, KEYTRUDA may provide better outcomes for some patients.

  • Melanoma: In a study involving advanced melanoma patients who had not previously received any treatment, the overall survival rate was significantly higher among those receiving KEYTRUDA than those undergoing standard chemotherapy.

  • Head and Neck Cancer: KEYTRUDA has shown promising results in treating recurrent or metastatic head and neck squamous cell carcinoma, with a higher overall response rate compared to standard chemotherapy.

  • Hodgkin Lymphoma: A study found that patients with relapsed or refractory classical Hodgkin lymphoma experienced an overall response rate of 69% when treated with KEYTRUDA.

The effectiveness of KEYTRUDA and signs that KEYTRUDA is working varies depending on the type and stage of cancer being treated. 

Is KEYTRUDA Covered by Medicare?

If you are an elderly patient considering KEYTRUDA treatments, it is essential to understand the financial implications and whether your insurance covers the cost. For most people on Medicaid, out-of-pocket costs for prescription medicines like KEYTRUDA range from $4 to $8 per infusion. However, Medicare coverage may differ.

Medicare Part B

In some cases, Medicare Part B (Medical Insurance) may cover KEYTRUDA if it is administered in a doctor's office or outpatient hospital setting. The exact coverage depends on your specific plan and circumstances. Generally speaking, you will be responsible for 20% of the approved amount after meeting your yearly deductible.

Medicare Part D

If you have a Medicare Prescription Drug Plan (Part D), it might also provide coverage for KEYTRUDA. Each plan has its formulary or list of covered drugs that include various cancer medications such as pembrolizumab (the generic name for Keytruda). To determine if your plan covers this drug specifically, consult with your insurance provider or review their formulary.

  • Note: Some patients may qualify for Extra Help through Social Security to assist with paying prescription drug costs under Medicare Part D.


A third option is obtaining coverage through a Medicare Advantage Plan (Part C). These plans are offered by private insurance companies and include both Medicare Part A (Hospital Insurance) and Part B benefits. Many also offer prescription drug coverage, which may cover KEYTRUDA.


What percentage of patients have Keytruda side effects?

Approximately 85% of patients taking Keytruda experience some side effects, including decreased appetite, hair loss, severe skin reactions, weight loss, muscle pain, increased sweating, and eye problems. Most side effects are mild to moderate and can be managed with proper medical care.

What are the major Keytruda side effects?

Major side effects or life threatening issues of Keytruda include severe reactions such as blindness or other eye problems, difficulty with breathing, inability to speak, seizures, paralysis in the arms and legs, and more

What should I avoid while on KEYTRUDA?

While receiving KEYTRUDA infusions, avoid exposure to infections, decrease your time in direct sunlight, and avoid strenuous exercise. 


In conclusion, Keytruda is a medication used to treat cancer that works by stimulating the immune system. However, like any other medication, it has side effects such as fatigue, nausea and vomiting, weight loss, skin reactions, and eye problems, among others. Despite its potential side effects, Keytruda has been demonstrated to be effective in treating a variety of life threatening cancers including melanoma and lung cancer.

If you are a senior considering utilizing Keytruda or any other medication for your condition, it is essential to converse with your doctor before settling on any decisions. Also, remember that Medicare may cover some or all of the costs associated with this treatment depending on your plan.

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