Keytruda (Pembrolizumab)

Keytruda is used in oncology to target the PD‑1 pathway across several solid tumours and lymphomas.

• Melanoma: improves overall survival and disease‑free survival in patients with advanced or metastatic disease.
• Non‑small cell lung cancer: extends progression‑free and overall survival in metastatic NSCLC expressing PD‑L1.
• Head and neck squamous cell carcinoma: enhances response rates and survival in recurrent or metastatic disease.
• Classical Hodgkin lymphoma: achieves high response rates in relapsed or refractory cases.
• Urothelial carcinoma: provides durable responses in locally advanced or metastatic disease.
• MSI‑high solid tumours: offers tumor‑agnostic efficacy in microsatellite instability‑high or mismatch repair‑deficient cancers.

• Pembrolizumab is a humanized IgG4 monoclonal antibody that binds to the programmed death‑1 (PD‑1) receptor on activated T‑cells. By blocking PD‑1 interaction with its ligands PD‑L1 and PD‑L2, the drug releases the inhibitory checkpoint, restoring T‑cell mediated immune surveillance and enabling the immune system to recognize and destroy tumor cells. This reactivation of anti‑tumor immunity can lead to tumor regression across multiple cancer types.

Pembrolizumab may cause a range of adverse reactions, varying from mild to severe.

Common Side Effects

• Fatigue: persistent tiredness affecting daily activities.
• Rash: skin irritation that may be itchy or red.
• Diarrhea: loose stools that can lead to dehydration.
• Nausea: feeling of sickness often accompanied by vomiting.
• Arthralgia: joint pain or stiffness.
• Pruritus: generalized itching without rash.

Serious or Rare Side Effects

• Immune‑mediated pneumonitis: inflammation of lung tissue that can impair breathing.
• Colitis: severe inflammation of the colon causing abdominal pain and diarrhea.
• Hepatitis: liver inflammation leading to elevated enzymes.
• Endocrinopathies: thyroiditis, adrenal insufficiency, or hypophysitis affecting hormone balance.
• Nephritis: kidney inflammation that may reduce renal function.
• Severe skin reactions: Stevens‑Johnson syndrome or toxic epidermal necrolysis.
• Myocarditis: inflammation of heart muscle that can affect cardiac function.

When using Keytruda, clinicians should observe several precautionary measures to ensure patient safety.

• Monitor immune-related adverse events: assess patients regularly for signs of inflammation in organs such as lungs, liver, colon, and endocrine glands.
• Evaluate baseline organ function: obtain liver, renal and thyroid function tests before initiating therapy.
• Use caution in patients with pre‑existing autoimmune disease: weigh benefits against risk of exacerbation.
• Avoid live vaccines during treatment: immunosuppression may reduce vaccine efficacy and increase infection risk.
• Discontinue or delay treatment for severe toxicities: follow established management guidelines for grade 3‑4 events.
• Store at 2-8°C: keep refrigerated, protect from light, do not freeze or shake.

Pembrolizumab can interact with other medicines, influencing its efficacy or safety profile.

Major Interactions (Avoid)

• High‑dose systemic corticosteroids: may diminish pembrolizumab’s immune‑activating effect.
• Live attenuated vaccines: increased risk of infection due to immune modulation.
• Organ transplant immunosuppressants: heightened risk of graft rejection or severe immune reactions.

Moderate Interactions (Monitor Closely)

• Other immune checkpoint inhibitors: overlapping toxicities require careful monitoring.
• Anticoagulants: potential for increased bleeding if immune‑mediated thrombocytopenia occurs.
• Hormone replacement therapy for endocrine toxicities: adjust dosing based on thyroid or adrenal function changes.