Erlotinib

• PO: 25 mg, 100 mg, 150 mg

• Take on an empty stomach:
  → At least 1 hour before or 2 hours after food
• Swallow tablets whole with water
• Do not crush or chew
• Consistency in timing is important for drug levels
• Avoid grapefruit juice (may alter metabolism)

• Class: Tyrosine kinase inhibitor (TKI)
• Mechanism of Action:
  Erlotinib inhibits the epidermal growth factor receptor (EGFR) tyrosine kinase, blocking signal transduction pathways that lead to tumor cell proliferation and survival.
• Bioavailability: ~60% (↑ with high-fat meals)
• Metabolism: Hepatic (CYP3A4 primary; also CYP1A2, CYP1A1)
• Half-life: ~24–36 hours
• Excretion: Feces (~90%), urine (~9%)

• Rash (acneiform) – correlates with drug activity
• Diarrhea
• Fatigue
• Loss of appetite
• Dry skin
• Nausea, vomiting
• Conjunctivitis or eye irritation

• Hypersensitivity to erlotinib or any component of the formulation
• Use with caution in patients with preexisting interstitial lung disease, liver dysfunction, or peptic ulcer disease

• CYP3A4 inducers (e.g., rifampin, phenytoin) ↓ erlotinib levels
• CYP3A4 inhibitors (e.g., ketoconazole, clarithromycin) ↑ toxicity risk
• Proton pump inhibitors (PPIs) and H2 blockers ↓ absorption of erlotinib
• Smoking increases metabolism via CYP1A1 → ↓ drug efficacy

Warfarin: Increased INR and bleeding risk