Imatinib

Kinase inhibitors (targeted oncology)
Kinase inhibitors (targeted oncology)
High alert
An error with this medicine can cause serious harm: double checks and protocols are used.

The first targeted kinase inhibitor: it shuts down BCR-ABL in Philadelphia-positive CML and KIT in GIST. Typical effects: oedema, cramps, nausea.

Updated Nov 1, 2026

Also called: imatinib mesylate, STI571

Quick facts

Group: Kinase inhibitors (targeted oncology)
Target: BCR-ABL tyrosine kinase (ABL1 kinase domain)
Used for: KIT · Hypereosinophilic syndrome
Key effects: Oedema · Nausea · Rash
Monitor: Complete blood count · Liver function before starting
ATC: L01EA01

No doses: the clinician sets them by the current guideline.

Mechanism of action

BCR-ABL tyrosine kinase (ABL1 kinase domain)Imatinib

The figure shows imatinib in the ATP pocket of the mouse c-Abl kinase domain, whose site matches the human enzyme; it holds the kinase in its inactive shape.

Target in 3D: BCR-ABL tyrosine kinase (ABL1 kinase domain). PDB structure 1IEP (RCSB PDB, public domain). View the structure at RCSB PDB

The Philadelphia chromosome, t(9;22), fuses BCR to ABL and creates BCR-ABL, a tyrosine kinase that is always switched on and drives chronic myeloid leukaemia. Imatinib occupies the ATP-binding pocket and locks the kinase in its inactive conformation, so it cannot phosphorylate its substrates; the leukaemic cells stop proliferating and undergo apoptosis. It also inhibits the receptor kinases KIT and PDGFR, which explains its activity in GIST and some eosinophilic disorders.

t(9;22) creates the always-active BCR-ABL kinase
Imatinib fills the ATP pocket, inactive shape locked
No substrate phosphorylation: proliferation stops
Also blocks KIT and PDGFR (GIST)

Indications

Philadelphia chromosome-positive chronic myeloid leukaemia, in adults and children. Chronic myeloid leukaemia →
Philadelphia-positive acute lymphoblastic leukaemia. Acute leukaemia (AML and ALL) →
KIT (CD117)-positive gastrointestinal stromal tumour, advanced or after resection. Gastrointestinal stromal tumour (GIST) →
Hypereosinophilic syndrome, chronic eosinophilic leukaemia, PDGFR-rearranged myelodysplastic/myeloproliferative disease, systemic mastocytosis and dermatofibrosarcoma protuberans.

Adverse effects

Common

Oedema, especially around the eyes, and fluid retention
Nausea, vomiting, diarrhoea, abdominal pain
Muscle cramps and musculoskeletal pain
Rash
Fatigue

Contraindications

No absolute contraindications in the label; used with caution in heart disease, liver impairment and pregnancy

Key interactions

Strong CYP3A4 inducers (rifampicin, carbamazepine, phenytoin, St John's wort): Lower imatinib levels and can cause loss of response.
Strong CYP3A4 inhibitors (ketoconazole, clarithromycin): Raise imatinib levels and toxicity.
CYP3A4 substrates (e.g. simvastatin): Imatinib raises their levels.
Warfarin: Anticoagulation with heparin or low-molecular-weight heparin is preferred to warfarin.
Levothyroxine after thyroidectomy: Hypothyroidism can appear; TSH is followed closely.

What is monitored

Complete blood count, frequently in the first months
Liver function before starting and regularly
Body weight and oedema
Kidney function
BCR-ABL transcript levels (molecular response) in CML
Growth in children

Administration and safety

Oral; taken with a meal and a large glass of water to reduce stomach upset.
For people who cannot swallow tablets, the label allows dispersing them in water or apple juice just before taking them.
Check the drug name carefully: imatinib, dasatinib and nilotinib are different drugs with different food and safety rules.
Avoid grapefruit and St John's wort, which change its levels through CYP3A4.

Pregnancy and breastfeeding

Can harm the fetus; effective contraception is used during treatment, and breastfeeding is not advised.

Nursing care

Weigh the patient regularly and look for periorbital and leg swelling; report rapid weight gain.
Review blood counts and liver tests before refills as ordered.
Ask about breathlessness, chest pain or black stools.
Teaching: take it every day as prescribed, report fever or bleeding, use contraception, and be careful driving if dizzy or tired.

Pharmacokinetics

Absorption: Oral; almost completely absorbed and taken with a meal and a large glass of water.
Metabolism: Liver, mainly CYP3A4, to an active N-desmethyl metabolite; it also inhibits CYP3A4 and CYP2D6.
Elimination: Mostly in the faeces as metabolites; a small part in urine.
Half-life: About 18 hours (about 40 hours for the active metabolite).

Test yourself

Think of the answer, then tap the question to see it.

What does imatinib inhibit in chronic myeloid leukaemia?

The BCR-ABL tyrosine kinase produced by the Philadelphia chromosome t(9;22).

Which solid tumour responds to imatinib, and through which target?

Gastrointestinal stromal tumour (GIST), through KIT (CD117).

A patient on imatinib gains weight quickly and has swollen eyelids. What is happening?

Fluid retention, a typical imatinib effect; it may progress to effusions and must be reported.

Why can rifampicin make imatinib fail?

It induces CYP3A4 and lowers imatinib levels.

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Connections

← Back to the class: Kinase inhibitors (targeted oncology)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: DailyMed - IMATINIB MESYLATE- imatinib tablet, film coated (DailyMed (U.S. National Library of Medicine), 2026); Imatinib: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2025); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.