Imatib 400 Tablet contains Imatinib mesylate 400 mg, a selective tyrosine kinase inhibitor used primarily in the treatment of chronic myeloid leukemia (CML) and gastrointestinal stromal tumors (GISTs). Imatinib mesylate functions by inhibiting the BCR-ABL tyrosine kinase, an abnormal enzyme produced by the Philadelphia chromosome in CML, thereby preventing the proliferation of malignant cells. It also targets other tyrosine kinases such as c-KIT and PDGF receptors, which are implicated in GISTs. Imatib 400 is indicated for newly diagnosed Philadelphia chromosome-positive CML in chronic phase, accelerated phase, or blast crisis, as well as for patients resistant or intolerant to prior therapy. Additionally, it is prescribed for unresectable and/or metastatic malignant GISTs expressing the c-KIT protein. The medication is administered orally, with dosage individualized based on disease phase and patient response. Common adverse effects include edema, nausea, muscle cramps, rash, and fatigue, though serious side effects such as myelosuppression and hepatotoxicity may occur and require monitoring. Regular hematologic and biochemical assessments are recommended during treatment. Imatib 400 should be used under strict medical supervision, with consideration of potential drug interactions and contraindications to optimize therapeutic outcomes.