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What Is Selumetinib?

Selumetinib is a prescription kinase inhibitor marketed under the brand name Koselugo. It is approved for adults and children aged one year and older with neurofibromatosis type 1 who have symptomatic, inoperable plexiform neurofibromas. These tumors develop along nerves and can cause pain, disfigurement, weakness, or impaired function. Selumetinib targets an intracellular signaling pathway involved in tumor growth. It is available as oral capsules and oral granules, with doses determined by body surface area. Selumetinib can reduce tumor volume in eligible patients but does not cure neurofibromatosis type 1. Treatment requires monitoring of heart function, vision, gastrointestinal effects, and skin reactions.

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What Is Selumetinib?

Selumetinib is a prescription kinase inhibitor marketed under the brand name Koselugo. It is approved for adults and children aged one year and older with neurofibromatosis type 1 who have symptomatic, inoperable plexiform neurofibromas. These tumors develop along nerves and can cause pain, disfigurement, weakness, or impaired function. Selumetinib targets an intracellular signaling pathway involved in tumor growth. It is available as oral capsules and oral granules, with doses determined by body surface area. Selumetinib can reduce tumor volume in eligible patients but does not cure neurofibromatosis type 1. Treatment requires monitoring of heart function, vision, gastrointestinal effects, and skin reactions.

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How Does Selumetinib Work?

Selumetinib inhibits MEK1 and MEK2, enzymes involved in the RAS-RAF-MEK-ERK signaling pathway. This pathway regulates cell growth and survival. Neurofibromatosis type 1 results from changes in the NF1 gene, which normally helps regulate RAS signaling. When this regulation is impaired, excessive pathway activity can contribute to the development of plexiform neurofibromas. Blocking MEK activity can reduce signaling that supports tumor growth and may shrink existing tumors. Selumetinib does not repair the NF1 gene or eliminate every manifestation of neurofibromatosis. Its activity against MEK can also affect normal tissues, contributing to cardiovascular, ocular, and other adverse reactions.

What Condition Does Selumetinib Treat?

Selumetinib is approved for adult and pediatric patients aged one year and older with neurofibromatosis type 1 and symptomatic, inoperable plexiform neurofibromas. These noncancerous nerve tumors may involve critical structures or grow in ways that make complete surgical removal unsafe. Symptoms can include pain, difficulty moving, disfigurement, or pressure on nearby tissues. The FDA expanded the pediatric indication to children aged one year and older in September 2025 and approved treatment for adults in November 2025. Selumetinib is not approved for every NF1-related tumor or other complications of neurofibromatosis. A specialist confirms tumor characteristics, symptoms, and treatment eligibility before prescribing it.

How Should Selumetinib Be Taken?

Selumetinib is taken orally twice daily, with the recommended dose based on body surface area. The general starting dose is 25 mg/m? twice daily, subject to the available dosage strengths and body surface area-based tables in the prescribing information. Koselugo capsules and oral granules have different administration instructions and minimum body surface area requirements. Capsules should be swallowed whole rather than opened or crushed. Oral granules are intended for patients who cannot swallow capsules and must be administered according to the product instructions. Treatment continues until disease progression or unacceptable toxicity. Clinicians assess cardiac function, perform eye examinations, and monitor laboratory results before and during therapy.

What Are the Side Effects and Warnings of Selumetinib?

Common adverse effects include vomiting, diarrhea, abdominal pain, rash, fatigue, and nail changes. Serious risks include reduced left ventricular ejection fraction, which can indicate heart muscle dysfunction, and ocular toxicity such as retinal pigment epithelial detachment or retinal vein occlusion. Selumetinib can also cause severe skin reactions, muscle injury with elevated creatine phosphokinase, gastrointestinal toxicity, and embryo-fetal harm. Koselugo capsules contain vitamin E, which can increase bleeding risk in certain patients. Heart function testing and comprehensive ophthalmic examinations are recommended before and during treatment. New blurred vision, vision loss, chest symptoms, severe muscle pain, or persistent gastrointestinal problems require medical evaluation.

Common Questions About Selumetinib

Is selumetinib the same as Koselugo?

Yes. Koselugo contains selumetinib, a MEK inhibitor used for symptomatic, inoperable plexiform neurofibromas associated with neurofibromatosis type 1.

Can adults receive selumetinib?

Yes. The FDA approved Koselugo for eligible adults with NF1-related symptomatic, inoperable plexiform neurofibromas in November 2025.

Can young children receive selumetinib?

Yes. Koselugo is approved for children aged one year and older who meet the treatment criteria. Doses depend on body surface area and formulation.

Can selumetinib affect eyesight?

Yes. Selumetinib can cause serious retinal complications. Eye examinations are recommended, and new visual symptoms require prompt assessment.

References

DailyMed - KOSELUGO (selumetinib) capsules and oral granules. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=7d042c61-f28f-4ab5-ab10-d7558c0d49ff. Date Accessed November 6, 2026.

Koselugo. European Medicines Agency. https://www.ema.europa.eu/en/medicines/human/EPAR/koselugo. Date Accessed November 6, 2026.

Selumetinib. LiverTox. https://www.ncbi.nlm.nih.gov/books/NBK569419/. Date Accessed November 6, 2026.

Selumetinib. MedlinePlus. https://medlineplus.gov/druginfo/meds/a620030.html. Date Accessed November 6, 2026.

Selumetinib. PubChem. https://pubchem.ncbi.nlm.nih.gov/compound/Selumetinib. Date Accessed November 6, 2026.