Gleevec (Imatinib): What It Is and What to Expect

Imatinib is a kinase inhibitor. A kinase is an enzyme. It hands a growth signal on inside a cell.

In chronic myeloid leukemia, parts of chromosomes 9 and 22 trade places. The short chromosome 22 that results is called the Philadelphia chromosome. It carries a fused gene, BCR-ABL. The protein it builds is a kinase stuck in the on position. Imatinib slots into the pocket where that protein takes its fuel. The signal stops.

The same pill blocks two other kinases. One is KIT. The other is the platelet-derived growth factor receptor, or PDGFR. That is why one drug treats diseases that look unrelated. Each of them runs on a kinase this molecule happens to fit. Imatinib is the drug that made targeted therapy a real category rather than a hope.

Gleevec is the original US brand name. An oral solution is sold as Imkeldi. The generic name is imatinib mesylate.

NCI's drug page was last updated on 9 January 2025. It lists more settings than most people expect:

• Chronic myeloid leukemia that is Philadelphia chromosome positive. This covers adults and children in newly diagnosed chronic phase. It also covers chronic, accelerated or blast phase that got worse after interferon-alpha.
• Acute lymphoblastic leukemia that is Philadelphia chromosome positive. In adults, disease that came back or did not respond. In children, given with chemotherapy as the first treatment.
• Gastrointestinal stromal tumor that carries the KIT protein. It must be one that surgery cannot remove, or that has spread.
• The same tumor after complete surgery, when it is KIT-positive.
• Dermatofibrosarcoma protuberans in adults. It must have returned, spread, or be one surgery cannot remove.
• Myelodysplastic and myeloproliferative neoplasms with an abnormal PDGFR gene.
• Aggressive systemic mastocytosis. The p.D816V c-KIT variant must be absent, or its status unknown.
• Chronic eosinophilic leukemia or hypereosinophilic syndrome in adults.

Notice the pattern. Several entries turn on a gene result, not on the organ involved. That is the whole logic of biomarker testing.

Gleevec comes as scored tablets. There are two strengths, 100 mg and 400 mg. The starting dose depends on the disease:

• Chronic-phase CML in adults: 400 mg a day.
• Accelerated phase or blast crisis: 600 mg a day.
• Children with newly diagnosed CML: an amount worked out from body size, up to a daily ceiling set by the label.
• Adults with ALL that came back or did not respond: 600 mg a day.
• GIST that has spread or cannot be removed: 400 mg a day. A rise to 800 mg is possible if the disease clearly grows.
• GIST after complete surgery: 400 mg a day. The label recommends three years.
• The three rarer blood conditions above: 400 mg a day. Two of them are driven by a FIP1L1-PDGFR-alpha fusion. For those, the label starts at 100 mg a day.

Two instructions are easy to miss. Every dose goes down with a meal and a large glass of water. That is because imatinib irritates the gut. And 400 mg or 600 mg is taken once daily. A dose of 800 mg is split into 400 mg twice a day. Tablets may be dissolved in water or apple juice by anyone who cannot swallow them.

The list above is the label's, condition by condition. It is not a guide to your own treatment: only your haematology or oncology team can say which amount applies to you, and they change it based on your response and blood tests.

The label groups the reactions reported in at least 30 percent of people. They are swelling, nausea, vomiting, muscle cramps, aching muscles and bones, diarrhea, rash, fatigue and belly pain.

Swelling is the signature one. It shows up most often around the eyes or in the lower legs. The label describes managing it with a water pill, with other supportive care, or by lowering the dose. Severe surface swelling was reported in about 1.5 to 6 percent of people in the CML studies.

Side effects say nothing about whether the drug is working. The label's own rules for raising a dose use two other measures. One is blood response after at least three months. The other is chromosome response after six to twelve months.

The Gleevec label attaches set schedules. That is why appointments are frequent at the start:

• Complete blood counts frequently in the first two months, then periodically — your team sets the dates, and the early ones matter most.
• Liver tests before the first dose and regularly after that. Severe liver injury is uncommon. But fatal cases have been reported, and so have cases needing a transplant.
• Kidney function at the start and during treatment. In pooled label data, median estimated GFR fell from 85 to 75 mL/min/1.73 m2 over twelve months. By five years it was 69.
• Thyroid-stimulating hormone in anyone on levothyroxine after thyroid surgery. Imatinib can tip them into an underactive thyroid.
• Growth in children and pre-teens. Growth retardation has been reported. The long-term effect is unknown.

The label also warns of harm to a fetus. It asks for effective contraception during treatment, and for 14 days after the last dose.

Two facts are worth stating plainly. Gleevec carries no boxed warning. Its contraindications section reads "None."

That is not the same as no risk. Several serious problems sit under Warnings and Precautions. Fluid around the lungs or heart. Heart failure. Bleeding in the gut. A hole in the gut wall. Blistering skin reactions such as Stevens-Johnson syndrome. Tumor lysis syndrome, in which many cancer cells die at once and flood the blood.

Other medicines matter here. Strong CYP3A4 inducers cut imatinib levels. Rifampin, carbamazepine and phenytoin are examples. Strong inhibitors such as ketoconazole raise levels instead. The label says grapefruit juice should be avoided for that same reason.

The current label lives at DailyMed. The maker has to keep it up to date. A pharmacist can match those sections against one person's other medicines. A general page cannot. Anything sudden is an emergency whatever cancer drug is involved. That means trouble breathing, chest pain, a high fever, confusion, or heavy bleeding. Those belong on the care team's emergency number, or in an emergency department. What this drug is meant to achieve in one case belongs in the treatment plan.

• https://www.cancer.gov/about-cancer/treatment/drugs/imatinibmesylate
• https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=211ef2da-2868-4a77-8055-1cb2cd78e24b