Imatinib mesylate is a first-generation, small-molecule, tyrosine kinase inhibitor (TKI) that revolutionized the treatment of Philadelphia chromosome-positive (Ph+) leukemias and certain other malignancies. It acts as a competitive inhibitor at the ATP-binding site of specific tyrosine kinases, most notably the BCR-ABL fusion protein, c-KIT, and PDGFR. In the Indian context, it is a critical, life-saving targeted therapy for Chronic Myeloid Leukemia (CML) and Gastrointestinal Stromal Tumors (GIST), available through multiple domestic manufacturers, making it more accessible.
Adult: CML Chronic Phase: 400 mg orally once daily. CML Accelerated Phase/Blast Crisis: 600 mg orally once daily. Ph+ ALL: 600 mg orally once daily. GIST (Unresectable/Metastatic): 400 mg orally once daily. GIST (Adjuvant): 400 mg orally once daily. Doses may be escalated to 600 mg or 800 mg (400 mg twice daily) in case of disease progression, inadequate response, or loss of response, if tolerated.
Note: Take with a meal and a large glass of water to minimize gastrointestinal irritation. The tablet should be swallowed whole. If unable to swallow, it can be dispersed in a glass of water or apple juice (approximately 50 mL for a 100 mg tablet, 200 mL for a 400 mg tablet), stir, and drink immediately. For pediatric use, the suspension can be administered via nasogastric tube. Missed Dose: If a dose is missed, take it as soon as remembered unless it is nearly time for the next dose. Do NOT double the dose.
Imatinib is a 2-phenylaminopyrimidine derivative that functions as a potent and selective competitive inhibitor of the ATP-binding site on several tyrosine kinase enzymes. It binds to the inactive, non-ATP-binding conformation of the kinase, stabilizing it and preventing the conformational shift required for ATP binding and subsequent autophosphorylation and substrate phosphorylation. This halts the downstream signaling cascades (e.g., RAS/RAF/MEK/ERK, JAK/STAT, PI3K/AKT) that drive uncontrolled cellular proliferation and survival.
Pregnancy: Pregnancy Category D. Imatinib is teratogenic and embryotoxic in animals. Women of childbearing potential must use highly effective contraception during and for at least 15 days after stopping therapy. If pregnancy occurs, the patient should be apprised of the potential hazard to the fetus.
Driving: Patients may experience dizziness, blurred vision, or fatigue. Caution is recommended when driving or operating machinery until their individual response is known.
| Strong CYP3A4 Inhibitors (e.g., Ketoconazole, Itraconazole, Voriconazole, Clarithromycin, Ritonavir, Grapefruit juice) | Increase imatinib plasma concentrations, increasing risk of toxicity. | Major |
| Strong CYP3A4 Inducers (e.g., Rifampicin, Phenytoin, Carbamazepine, Phenobarbital, St. John's Wort) | Decrease imatinib plasma concentrations, potentially leading to loss of efficacy. | Major |
| Warfarin | Imatinib may inhibit its metabolism via CYP2C9. Use low molecular weight heparin instead. | Major |
| Simvastatin, Lovastatin | Increased risk of myopathy/rhabdomyolysis as both are CYP3A4 substrates. | Moderate |
| P-Glycoprotein Inhibitors (e.g., Cyclosporine) | May increase imatinib absorption and plasma levels. | Moderate |