Imatinib

Imatinib is an oral targeted anticancer medicine belonging to the tyrosine kinase inhibitor class. It works by blocking specific proteins that contribute to the growth and survival of certain cancer cells. Its principal targets include BCR::ABL1, an abnormal protein produced by the Philadelphia chromosome in chronic myeloid leukaemia (CML), and receptor tyrosine kinases such as KIT and platelet-derived growth factor receptors (PDGFR). By inhibiting these proteins, imatinib helps reduce abnormal cell signalling and control the growth of susceptible cancer cells. Unlike conventional chemotherapy, which generally affects a broad range of rapidly dividing cells, imatinib targets particular molecular pathways involved in selected cancers. It is available as oral tablets and is usually taken with food and a large glass of water to reduce gastrointestinal irritation. Imatinib is clinically important because it has substantially improved treatment outcomes for many patients with CML and is also used for selected gastrointestinal stromal tumours (GIST) and other uncommon malignancies with specific molecular characteristics. Treatment selection depends on the diagnosis, relevant genetic or molecular findings, disease stage, previous therapies, and the patient's overall health. Regular blood tests and clinical assessments are important to evaluate response, identify adverse effects, and guide dose adjustments during treatment.

Imatinib was developed through research into abnormal tyrosine kinase signalling, particularly the BCR::ABL1 protein associated with the Philadelphia chromosome in CML. Its introduction marked a major advance in molecularly targeted cancer treatment. The United States Food and Drug Administration (FDA) granted its initial approval for selected patients with CML in May 2001, with additional indications subsequently approved for other cancers. The European Commission authorised Glivec, an imatinib-containing medicine, in the European Union on 7 November 2001 following assessment by the European Medicines Agency (EMA). Subsequent approvals expanded its use to selected cases of Philadelphia chromosome-positive acute lymphoblastic leukaemia (Ph+ ALL), KIT-positive gastrointestinal stromal tumours, dermatofibrosarcoma protuberans, and certain PDGFR-associated or eosinophilic disorders. The approval status and authorised indications vary by country and product. Regulatory authorities, including the FDA, EMA, and India's Central Drugs Standard Control Organisation (CDSCO), oversee relevant product approvals and prescribing requirements within their jurisdictions. Clinical development included studies evaluating haematological, cytogenetic, and molecular responses in CML, as well as tumour response and recurrence outcomes in GIST. These studies established the role of imatinib in cancers driven by susceptible tyrosine kinase abnormalities. Its use continues to depend on the applicable product information and the specific disease being treated.

Imatinib is used to treat selected cancers and blood disorders in which specific tyrosine kinases contribute to disease development. Its principal indications include Philadelphia chromosome-positive chronic myeloid leukaemia in adults and children, according to approved age and disease criteria, and Philadelphia chromosome-positive acute lymphoblastic leukaemia, where it may be combined with chemotherapy or used alone in certain adults with relapsed or refractory disease. It is also used for KIT-positive gastrointestinal stromal tumours that cannot be removed surgically or have spread, and as adjuvant treatment after surgery in eligible patients at significant risk of recurrence. Other approved uses include selected cases of myelodysplastic or myeloproliferative diseases associated with PDGFR gene rearrangements, advanced hypereosinophilic syndrome or chronic eosinophilic leukaemia with specific molecular abnormalities, and unresectable, recurrent, or metastatic dermatofibrosarcoma protuberans when surgery is unsuitable. The precise indication depends on the diagnosis, molecular findings, disease stage, previous treatment, and local regulatory approval. Imatinib may be used as monotherapy or in combination with other anticancer medicines, depending on the condition and treatment protocol.

Imatinib is administered orally, generally with a meal and a large glass of water to reduce stomach irritation. The adult dose depends on the indication, disease phase, response to treatment, tolerability, and applicable prescribing information. For many adults with chronic-phase CML, the usual starting dose is 400 mg once daily, while accelerated-phase or blast-phase CML commonly requires 600 mg daily. Selected patients with Ph+ ALL, GIST, or other approved conditions may require different regimens, often within the range of 400–800 mg daily depending on the indication. Higher daily doses may be divided into two administrations when specified by the prescribing information. Paediatric dosing is generally calculated according to body surface area and must be supervised by an experienced specialist. Treatment is often continued long term while the medicine remains effective and tolerable, or until disease progression or unacceptable toxicity occurs. Dose interruption or adjustment may be necessary for significant adverse effects, blood-count abnormalities, liver dysfunction, or fluid retention. Regular clinical review and laboratory monitoring are essential throughout treatment.

Common side effects of imatinib include nausea, vomiting, diarrhoea, abdominal discomfort, indigestion, muscle cramps, muscle or joint pain, fatigue, headache, skin rash, and swelling around the eyes or in the limbs. Fluid retention and weight gain may occur, sometimes becoming clinically significant. Changes in blood counts, including anaemia, reduced neutrophil counts, and reduced platelet counts, are also possible. Some patients develop changes in liver enzyme levels or experience reduced appetite. The frequency and severity of adverse effects vary according to the dose, underlying disease, treatment duration, and individual health. Taking the medicine with food and water may help reduce gastrointestinal discomfort. Patients should report persistent symptoms, unexpected weight gain, or increasing swelling to their healthcare professional. Supportive treatment, closer monitoring, or dose modification may help manage side effects when clinically appropriate.

Imatinib can cause serious adverse reactions, including severe fluid retention, heart failure in susceptible patients, significant liver injury, severe reductions in blood-cell counts, gastrointestinal bleeding, and, rarely, severe skin reactions. Tumour-related bleeding or gastrointestinal perforation may occur in certain patients with GIST, particularly in the context of the underlying disease. Liver function abnormalities can occasionally progress to serious injury, so prompt assessment is necessary if symptoms such as jaundice, dark urine, or persistent abdominal pain develop. Marked swelling, rapid weight gain, shortness of breath, unusual bleeding, fever, or signs of serious infection require urgent medical evaluation. Tumour lysis syndrome may occur in patients with a high tumour burden, and appropriate preventive measures should be considered when indicated. Treatment may need to be interrupted, reduced, or discontinued if serious toxicity develops. Imatinib can harm a developing fetus, so pregnancy risks and appropriate contraception should be discussed before and during treatment. Patients should follow specialist guidance and should not independently stop or change their prescribed dose.

Before starting imatinib, healthcare professionals should assess complete blood counts, liver and kidney function, relevant disease markers, fluid-retention risk, and the patient's medication history. Monitoring should continue at intervals appropriate to the indication and clinical condition. Patients with pre-existing heart disease, liver impairment, kidney impairment, or a history of significant oedema may require additional precautions. Pregnancy should be avoided during treatment, and breastfeeding considerations should be discussed with the treating clinician. Imatinib is metabolised mainly through the CYP3A4 enzyme system, so medicines that inhibit or induce this pathway may alter its concentration and effectiveness. Examples include certain azole antifungals, macrolide antibiotics, rifampicin, and some antiseizure medicines. Imatinib may also affect the metabolism of other medicines, including certain anticoagulants and drugs with a narrow therapeutic range. Grapefruit products may increase exposure and should be discussed with the healthcare team. Patients should inform their prescriber and pharmacist about all prescription medicines, over-the-counter products, and herbal supplements before starting or changing treatment.

Prescribers and pharmacists should confirm the diagnosis and relevant molecular findings before initiating imatinib, particularly BCR::ABL1 status in CML and appropriate KIT or PDGFR-related findings where relevant. Establish baseline blood counts, liver and kidney function, weight, and fluid-retention status, and document disease-specific response markers. Counsel patients to take the medicine with food and a large glass of water, follow the prescribed schedule, and avoid doubling a missed dose without professional guidance. Review adherence, tolerability, and interacting medicines at every suitable follow-up. Monitor blood counts and liver function regularly, and assess molecular or tumour response according to the underlying condition. Patients should promptly report fever, unusual bruising or bleeding, jaundice, breathlessness, rapid weight gain, or significant swelling. Pharmacists should check product strength, storage instructions, dose changes, and potential interactions during dispensing. Coordination among oncology specialists, pharmacists, and other treating clinicians helps maintain treatment continuity and supports early recognition of toxicity.