Checkpoint Inhibitors

1. Concept & Mechanism

  • Immune checkpoints are regulatory pathways that keep T-cell activation in check to prevent autoimmunity.
  • Tumors exploit these checkpoints (e.g., PD-L1 expression) to evade immune destruction.
  • Checkpoint inhibitors block these pathways, releasing the brakes on T-cells → restored antitumor immune response.

2. Main Targets

Target Location Function Example Drugs
PD-1 (Programmed cell death receptor-1) T cells Inhibits T-cell activation when bound by PD-L1/PD-L2 Pembrolizumab, Nivolumab, Cemiplimab
PD-L1 (Programmed death ligand-1) Tumor cells, immune cells Binds PD-1 to suppress T cells Atezolizumab, Durvalumab, Avelumab
CTLA-4 (Cytotoxic T-lymphocyte–associated antigen 4) T cells Inhibits early T-cell activation in lymph nodes Ipilimumab

3. Key Oncology Indications

Checkpoint inhibitors are used across multiple cancers:

4. Dosing Principles

  • Given IV every 2–6 weeks, depending on agent and indication
  • Flat dosing now preferred (e.g., pembrolizumab 200 mg q3w or 400 mg q6w)
  • No premedication unless prior infusion reaction
  • Continue until disease progression or unacceptable toxicity, often capped at 2 years in curative-intent settings

5. Toxicity Profile (Immune-Related Adverse Events – irAEs)

Immune activation can affect any organ system:

System Common irAEs Monitoring
Skin Rash, pruritus, vitiligo Visual exam, symptom check
GI Colitis, diarrhea Stool frequency, abdominal pain
Liver Hepatitis (↑ LFTs) Baseline & periodic LFTs
Endocrine Hypo/hyperthyroidism, adrenal insufficiency, hypophysitis TSH, free T4, cortisol
Lungs Pneumonitis Monitor cough, dyspnea
Kidneys Nephritis Serum creatinine, urinalysis
Heart Myocarditis (rare) Monitor troponin, ECG if symptomatic

Onset:

  • Dermatologic → early (weeks)
  • Endocrine → variable (weeks–months)
  • GI/liver/lung → often within first 3–6 months but can be delayed

6. Pharmacist Management Notes

  • Grade ≥2 irAEs → withhold CPI, initiate corticosteroids (prednisone 1–2 mg/kg/day), taper over ≥4 weeks
  • Severe or refractory irAEs may require additional immunosuppressants (infliximab, mycophenolate, tocilizumab)
  • Patient education is critical — irAEs can occur months after discontinuation
  • Avoid high-dose steroids before CPI initiation unless needed for comorbidities (may blunt efficacy)

7. Checkpoint Inhibitor Quick Table

Drug Target Common Indications Usual Adult Dose
Pembrolizumab PD-1 Melanoma, NSCLC, bladder, HNSCC, many MSI-H tumors 200 mg IV q3w or 400 mg q6w
Nivolumab PD-1 Melanoma, RCC, NSCLC, HNSCC, Hodgkin 240 mg IV q2w or 480 mg q4w
Cemiplimab PD-1 CSCC, NSCLC, BCC 350 mg IV q3w
Atezolizumab PD-L1 NSCLC, SCLC, TNBC, bladder, HCC 1200 mg IV q3w
Durvalumab PD-L1 Stage III NSCLC (post-CRT), ES-SCLC, biliary tract 10 mg/kg q2w or 1500 mg q4w
Avelumab PD-L1 MCC, urothelial carcinoma 800 mg IV q2w
Ipilimumab CTLA-4 Melanoma, RCC (combo), MSI-H CRC 3 mg/kg IV q3w × 4 doses (varies)
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