Erlotinib works as an inhibitor of EGFR tyrosine kinase. It competes reversibly with ATP on the ATP binding site of the intracellular kinase domain.
Erlotinib produces cell cycle arrest at the G1/S checkpoint. This is explained by inhibition of phosphorylation of Rb (Retinoblastoma) protein. Hypophosphorylation of Rb results in inhibition of cellular growth.
Erlotinib is indicated for the treatment of non-small cell lung cancer (NSCLC). These tumor cells have excessive EGFR expression, so they are receptive to this chemotherapeutic agent.
In addition to lung cancer, erlotinib is approved for use in patients with locally advanced or metastatic pancreatic cancer. Erlotinib is often used in combination with another antineoplastic agent, gemcitabine, for this disease.
The most common side effect of this drug is skin rashes. They can appear in the first month of starting the medication and are dose-dependent. An acneiform rash affecting the chest and upper back or generalized xerosis (dry skin) are common presentations.
The other common side effect that can occur is diarrhea. It frequently occurs in the first 4 weeks after starting treatment. Dietary changes and antidiarrheal medication can be used to treat this side effect.
Since erlotinib is metabolized by hepatic cytochrome p450 enzymes (CYP1A2 and CYP3A4), patients should avoid ingesting grapefruit juice when taking this medication as it would inhibit metabolism.
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