Keytruda (Pembrolizumab)

Keytruda (pembrolizumab) is used in oncology to block the PD‑1 immune checkpoint pathway across several tumor types.

• Melanoma: improves overall survival in patients with unresectable or metastatic disease.
• Non‑small cell lung cancer: extends progression‑free survival in advanced stages.
• Classical Hodgkin lymphoma: achieves durable remission in relapsed or refractory cases.
• Urothelial carcinoma: enhances response rates in locally advanced or metastatic disease.
• Head and neck squamous cell carcinoma: increases disease‑free survival after chemoradiation.
• Renal cell carcinoma: contributes to longer overall survival in metastatic settings.

• Pembrolizumab binds to the programmed death‑1 (PD‑1) receptor on activated T cells, preventing its interaction with the ligands PD‑L1 and PD‑L2 expressed on tumor cells and antigen‑presenting cells. This blockade releases the inhibitory signal, restoring T‑cell activity and enabling the immune system to recognize and destroy cancer cells across multiple tumor types.

Keytruda may cause a range of adverse reactions, from mild to severe, reflecting its immune‑modulating activity.

Common Side Effects

• Fatigue: persistent tiredness affecting daily activities.
• Rash: skin redness or irritation.
• Pruritus: itching of the skin.
• Diarrhea: loose stools, sometimes watery.
• Nausea: feeling of sickness or urge to vomit.
• Arthralgia: joint pain or stiffness.

Serious or Rare Side Effects

• Immune‑mediated pneumonitis: inflammation of lung tissue.
• Colitis: severe inflammation of the colon.
• Hepatitis: liver inflammation with elevated enzymes.
• Endocrinopathies: thyroid dysfunction or adrenal insufficiency.
• Severe infusion reactions: hypotension, bronchospasm, or anaphylaxis.
• Myocarditis: inflammation of heart muscle, potentially life‑threatening.

Before initiating therapy with Keytruda, clinicians should assess patient history and monitor for immune‑related events.

• Monitor for immune‑mediated adverse events: watch for signs of organ inflammation such as pneumonitis or colitis.
• Evaluate baseline organ function: conduct liver, renal, and thyroid tests prior to treatment.
• Caution in patients with autoimmune disease: risk of exacerbation may be higher.
• Avoid live vaccines during therapy: immunosuppression can lead to infection.
• Discontinue or pause treatment for severe toxicities: follow established management guidelines.
• Store at 2-8°C: keep refrigerated, protect from light, do not freeze or shake.

Pembrolizumab may interact with other agents that affect immune function or share metabolic pathways.

Major Interactions (Avoid)

• Concurrent use with other immune checkpoint inhibitors: increased risk of severe immune reactions.
• Live vaccines: may cause uncontrolled infection due to immunosuppression.
• High‑dose corticosteroids: can diminish therapeutic efficacy.

Moderate Interactions (Monitor Closely)

• Immunosuppressive therapies (e.g., azathioprine): may reduce anti‑tumor response, require close monitoring.
• CYP450 substrates: generally low interaction, but monitor for altered drug levels in polypharmacy settings.