Trametinib

Trametinib is an oral targeted anticancer medicine belonging to the mitogen-activated protein kinase kinase (MEK) inhibitor class. It blocks MEK1 and MEK2, proteins involved in the MAPK signalling pathway, which helps regulate cell growth, division and survival. In certain cancers, mutations in the BRAF gene can cause this pathway to become abnormally active, promoting uncontrolled tumour growth. By inhibiting MEK, trametinib can reduce signalling through this pathway and slow cancer-cell growth in appropriately selected patients. It is commonly used with dabrafenib, a BRAF inhibitor, because blocking two points in the same pathway can improve treatment effectiveness in specific BRAF-mutated cancers. Trametinib may also be used alone for certain patients with BRAF-mutated melanoma, depending on the applicable treatment guidelines and prescribing information. It is taken orally as tablets or, where approved and available, as an oral solution. Treatment selection requires confirmation of the relevant tumour mutation using an appropriate validated test. Trametinib is used in selected cases of melanoma, non-small-cell lung cancer and thyroid cancer, with indications varying by country and patient group. Because it can affect the heart, eyes, lungs, skin and gastrointestinal system, treatment requires specialist supervision and regular monitoring.

Trametinib was developed as a targeted therapy to inhibit MEK proteins within the MAPK signalling pathway, which is involved in the growth and survival of cancer cells. It received its first approval from the US Food and Drug Administration (FDA) in May 2013 for unresectable or metastatic melanoma with specific BRAF mutations. The European Commission granted marketing authorisation for Mekinist in the European Union on 30 June 2014. Subsequent approvals expanded its use, particularly in combination with dabrafenib, for selected patients with melanoma, non-small-cell lung cancer, anaplastic thyroid cancer and other eligible BRAF-mutated tumours. European approvals also cover specified differentiated thyroid cancers, subject to the applicable criteria. Clinical development has included the METRIC trial in melanoma, COMBI studies evaluating trametinib with dabrafenib, and studies in BRAF-mutated lung and thyroid cancers. Regulatory indications and age criteria vary by country, so the current local prescribing information should be consulted before treatment.

Trametinib is used for selected cancers with specific BRAF mutations, confirmed through appropriate molecular testing. As monotherapy, it may be used for eligible patients with unresectable or metastatic BRAF V600E- or V600K-mutated melanoma who have not previously received a BRAF inhibitor. In combination with dabrafenib, it is indicated for selected patients with unresectable or metastatic melanoma, melanoma following complete surgical removal in specified settings, metastatic non-small-cell lung cancer with a BRAF V600E mutation, and locally advanced or metastatic anaplastic thyroid cancer with a BRAF V600E mutation when suitable local treatment options are unavailable. In the United States, additional indications include certain BRAF V600E-mutated solid tumours and low-grade glioma in eligible patients. Other jurisdictions may authorise different indications, including selected differentiated thyroid cancers. Treatment choice depends on tumour type, mutation status, previous therapy, patient age and the applicable regulatory approval.

Trametinib is taken orally, usually once daily, as tablets or an approved oral solution where available. The usual adult dose is 2 mg once daily, while paediatric dosing depends on body weight and the specific approved indication. Tablets should generally be taken on an empty stomach, at least one hour before or two hours after food, at approximately the same time each day. When used with dabrafenib, both medicines must be taken according to their respective prescribing instructions. Treatment may continue until disease progression or unacceptable toxicity; after surgery for melanoma, the combination is generally given for a defined course of up to twelve months in the applicable setting. Dose interruptions or reductions may be required for adverse reactions. Clinicians should assess cardiac function, skin changes, visual symptoms and other relevant safety parameters during treatment. Patients should not change their dose or stop therapy without consulting their oncology team.

Common side effects of trametinib include rash, diarrhoea, fatigue, swelling of the arms or legs, nausea and acne-like skin inflammation. When trametinib is combined with dabrafenib, fever, chills, headache, vomiting, joint pain, muscle pain and reduced appetite may also occur. Some patients experience dry skin, cough or changes in blood pressure. The frequency and severity of these effects depend on the treatment regimen, cancer type and individual patient. Many adverse effects can be managed through supportive care, monitoring or medically supervised dose adjustments. Patients should report persistent diarrhoea, recurrent fever, worsening rash, unusual swelling or other new symptoms promptly because these may require further assessment.

Trametinib can cause serious adverse reactions, including reduced heart-pumping function, retinal disorders and other eye problems, interstitial lung disease or pneumonitis, severe skin reactions, major bleeding, blood clots and gastrointestinal inflammation or perforation. When combined with dabrafenib, serious fever-related reactions and new primary malignancies may also occur. Rare but serious complications such as haemophagocytic lymphohistiocytosis have been reported. Treatment should be interrupted or permanently discontinued when indicated by the severity and type of adverse reaction. Baseline and follow-up assessment of left ventricular ejection fraction is important, and new visual disturbances require prompt ophthalmological evaluation. Unexplained respiratory symptoms should be assessed for possible lung toxicity. Trametinib can cause fetal harm, so pregnancy prevention and counselling are essential. Serious symptoms require immediate medical assessment rather than self-treatment.

Before starting trametinib, clinicians should confirm the relevant tumour mutation and review the patient's medical history, current medicines and baseline organ function. Cardiac assessment should include left ventricular ejection fraction, with repeat testing during treatment as recommended in the prescribing information. Patients should report visual changes, breathing difficulties, severe abdominal symptoms, bleeding, skin changes or signs of blood clots promptly. Skin examinations are particularly important when trametinib is used with dabrafenib because of the risk of new skin malignancies. Blood glucose monitoring may be necessary in patients with diabetes or pre-existing hyperglycaemia. Pregnancy, breastfeeding and potential effects on fertility should be discussed before treatment. Trametinib is not associated with the same broad range of metabolic drug interactions as many small-molecule medicines, but concomitant therapies can still affect safety and treatment planning. All prescription medicines, non-prescription products and supplements should be reviewed by the treating clinician or pharmacist.

Confirm BRAF mutation status using an appropriate validated test before initiating treatment and ensure that the prescribed regimen matches the patient's cancer type and local approval. Document baseline cardiac function, skin findings, relevant laboratory results and any existing visual or respiratory symptoms. Establish a schedule for cardiac monitoring, skin examinations and assessment of new symptoms throughout treatment. Counsel patients on taking trametinib on an empty stomach and maintaining a consistent daily schedule. When used with dabrafenib, explain the possibility of fever and chills and provide clear instructions for contacting the oncology team if these occur. Review adherence, tolerability and all concurrent medicines at follow-up visits. New visual disturbances, breathlessness, significant bleeding, severe abdominal pain or suspected cardiac dysfunction require prompt assessment. Dose changes, treatment interruptions and decisions about restarting therapy should follow the relevant prescribing guidance and specialist judgement.