The mechanism of clinical antitumor action of erlotinib is not fully characterized. Erlotinib inhibits the intracellular phosphorylation of tyrosine kinase associated with the epidermal growth factor receptor (EGFR). Specificity of inhibition with regard to other tyrosine kinase receptors has not been fully characterized. EGFR is expressed on the cell surface of normal cells and cancer cells.
Metabolism occurs in the liver. In vitro assays of cytochrome P450 metabolism showed that erlotinib is metabolized primarily by CYP3A4 and to a lesser extent by CYP1A2, and the extrahepatic isoform CYP1A1.
Symptoms of overdose include diarrhea, rash, and liver transaminase elevation. The most common adverse reactions (>50%) in NSCLC are rash, diarrhea, anorexia and fatigue. The most common adverse reactions (>50%) in pancreatic cancer are fatigue, rash, nausea and anorexia.