Is it IMATINIB MESYLATE? Imatinib is a drug used to treat certain types of cancer.Imatinib works by blocking an abnormal enzyme characteristic of the disease.Imatinib is the first approved drug to directly turn off the signal of a protein known to cause a cancer. Imatinib is rapidly absorbed when given by mouth, and is highly bioavailable: 98% of an oral dose reaches the bloodstream. Metabolism of imatinib occurs in the liver .Although the long-term side effects of imatinib have not yet been ascertained, research suggests that it is generally very well tolerated. Broadly, side effects such as edema, nausea, rash and musculoskeletal pain are common but mild.Rarely it has been assosciated with damage to heart muscles.