Imatinib mesylate is an enzyme inhibitor used for cancer therapy. Imatinib mesylate is also known as STI571 and is sold under the brand name, Gleevec. It was given the name STI571 during early development. STI stands for signal transduction inhibitor.
Imatinib mesylate is approved by the U. S. Food and Drug Administration to treat a rare cancer called chronic myeloid leukemia (CML). (CML is also called chronic myelogenous leukemia or chronic myelocytic leukemia, as well.)
Imatinib mesylate is the first drug of its kind developed. It fights cancer by turning off an enzyme called tyrosine kinase that causes CML cells to lose their ability to die so they can multiply at an abnormal rate. Its function is different from other cancer drugs because it specifically targets an enzyme that allows the growth of CML cells. This drug has been shown to significantly reduce the number of cancer cells in the blood and bone marrow of treated patients.
Patients who are diagnosed with CML in the three phases of disease can be treated with imatinib mesylate. Chronic myeloid leukemia appears to respond within one to three months following administration of this drug.
A doctor experienced in the treatment of patients with CML should initiate therapy.
To minimize the risk of gastrointestinal irritation, imatinib mesylate should be taken with food and a large glass of water. The recommended dosage varies according to clinical circumstances and phase of disease, but generally ranges between 300 and 600 mg per day. As long as the patient continues to benefit, treatment should be continued.
Studies have not been performed with imatinib mesylate to determine if it is a carcinogen (cancer-causing); therefore it is not known whether this drug may cause mutations or may have cancer-causing effects. In addition, imatinib mesylate's safety and effectiveness has not been established in pediatric patients.
- Fluid retention and edema. If patients experience swelling or weight gain from water retention, they should inform their doctor and should be closely monitored. Signs and symptoms of fluid retention should be closely monitored and patients should be weighed regularly. Appropriate treatment must be provided if an unexpected rapid weight gain occurs. The likelihood of edema is increased with higher doses and in those over age 65 years.
- gastrointestinal irritation
- hematologic toxicity (toxicity of the blood)
- hepatotoxicity (toxicity of the liver)
- toxicities from long-term use
Commonly reported side effects include nausea and vomiting, muscle cramps, edema (water retention), skin rash, diarrhea, heartburn, and headache. Serious side effects occur less frequently, but if they occur may include: severe edema liver toxicity, and the potential for bleeding especially in the elderly.
Imatinib mesylate interacts with many other drugs. In some cases, side effects may be increased because imatinib mesylate might increase blood levels of certain drugs. Alternatively, imatinib mesylate may decrease blood levels of the drugs, thus reducing their effectiveness. In addition, the blood levels of imatinib mesylate may rise or fall because of other drugs. Therefore, side effects of imatinib mesylate may be increased or effectiveness may be reduced. The patient must discuss all of their medications with their doctor due to many potential drug-drug interactions.
CYP3A4 is an enzyme that is predominately responsible for the metabolism of imatinib mesylate.
The following drugs or families of drugs may interact with imatinib mesylate:
- Inhibitors of the CYP3A4 family, such as ketoconazole, itraconazole, erythromycin.
- Co-medications that induce CYP3A4, such as dexamethasone, phenytoin, carbamazepine, rifampicin, phenobarbital or St. John's Wort). No formal studies have been conducted on these medications and imatinib mesylate together.
- CYP3A4 substrates, such as cyclosporine or pimozide.
- CYP3A4 metabolized drugs, such as certain HMGCoA reductase inhibitors, triazolo-benzodiazepines, and dihydropyridine calcium channel blockers.
- Warfarin. Patients needing anticoagulant therapy while taking imatinib mesylate should be prescribed low-molecular weight or standard heparin.
This list is not all-inclusive of all possible interactions. Patients must inform their doctors of any drugs they are taking in order to avoid drug interactions.
See Also Low molecular weight heparins
Crystal Heather Kaczkowski, MSc.
—An enzyme that is predominately responsible for the metabolism of imatinib mesylate.
—Any protein that acts as a catalyst, increasing the rate of a chemical reaction.
—A type of cancer in which the bone marrow produces an excessive number of abnormal (leukemic) white blood cells. White blood cells protect the body against infection but the abnormal cells suppress the production of normal white blood cells.
—An abnormal mass of tissue that serves no purpose. Tumors may be either benign (non-cancerous) or malignant (cancerous).