Koselugo (selumetinib)
An approved treatment for Neurofibromatosis Type 1.
The same compound appears under different names depending on the context. Here is how to identify Selumetinib wherever you encounter it, plus the key facts at a glance.
- Generic name
- Selumetinib
- Brand name
- Koselugo
- Development codes
- AZD6244, ARRY-142886
- Drug class
- MEK inhibitor
- Manufacturer
- Alexion / AstraZeneca Rare Disease
- How it's taken
- Taken twice daily as oral capsules, with or without food, or as oral granules sprinkled on or mixed with a small amount of soft food such as yogurt or fruit puree.
The first FDA-approved targeted therapy for NF1 plexiform neurofibromas. Selumetinib blocks the RAS/MAPK pathway that becomes overactive when the NF1 gene is mutated, shrinking inoperable tumors in children and adults.
Where Selumetinib fits
First-in-class MEK inhibitor approved for NF1 plexiform neurofibromas. Standard of care since 2020 for children with symptomatic, inoperable tumors. Now joined by mirdametinib (2025) as a second MEK inhibitor option, giving clinicians and patients a choice between two targeted therapies with different dosing schedules and side effect profiles.
How Selumetinib works
In NF1, mutations in the NF1 gene remove the brakes on a cell growth pathway called RAS/MAPK. Without the braking protein neurofibromin, this pathway stays constantly active, telling cells to grow and divide unchecked, which leads to tumor formation. Selumetinib works by blocking MEK1 and MEK2, two proteins that sit in the middle of this pathway and relay the growth signal.
By shutting down MEK, selumetinib effectively cuts the wire between the overactive RAS signal and the cell's growth machinery. Tumor cells stop receiving instructions to multiply, and existing tumors can shrink. In the pivotal SPRINT trial, the majority of children saw measurable tumor shrinkage, with many experiencing reduced pain and improved function.
Selumetinib was originally approved for pediatric patients aged 2 and older. Subsequent approvals expanded the indication to children as young as 1 year (September 2025) and to adults (November 2025), broadening access across the NF1 population.
Mechanism: Selective inhibitor of MEK1 and MEK2, blocking the overactive RAS/MAPK signaling pathway that drives tumor growth in NF1
Side effects and safety
The most common side effects in clinical trials were vomiting (most frequent, affecting roughly 80% of patients), diarrhea, nausea, rash and other skin reactions, abdominal pain, and musculoskeletal pain. Selumetinib can also cause eye problems including blurred vision and retinal issues, which require regular ophthalmologic monitoring. Heart function changes (decreased ejection fraction) have been reported and are monitored with periodic echocardiograms. Koselugo can raise the muscle enzyme CPK and can cause serious muscle breakdown (rhabdomyolysis), so CPK is checked before and during treatment; report muscle pain or weakness. Koselugo capsules contain vitamin E, so ask your doctor before taking vitamin E supplements, and bleeding risk may be higher with blood thinners or antiplatelet drugs (the oral granules do not contain vitamin E). Koselugo can harm an unborn baby, so patients who can become pregnant, and males with partners who can, should use effective birth control during treatment and for 1 week after the last dose. Most side effects are manageable with dose adjustments or supportive care.
This is not a complete list of side effects. Talk to your doctor or pharmacist about what to expect and when to seek medical attention.
Taking Selumetinib
Taken twice daily as oral capsules, with or without food, or as oral granules sprinkled on or mixed with a small amount of soft food such as yogurt or fruit puree. The dose is calculated based on body surface area at 25 mg/m² per dose. Capsules should be swallowed whole, not opened or crushed. Treatment continues as long as the patient is benefiting and tolerating the medication.
Availability and cost
Only available as the brand-name product.
Help paying for Koselugo
Pick your insurance to see which help fits. Drugmaker copay cards can't be used with Medicare, Medicaid or TRICARE; charity funds are the usual route there.
- Copay help
Eligible commercially insured patients may pay as little as $0 for KOSELUGO through the Koselugo CoPay Program. Must enroll in OneSource. Not for government insurance.
For: private insurance · source - Insurance and case manager help
OneSource provides help navigating health insurance, treatment education, and a local Patient Education Manager.
For: private insurance, Medicare, Medicaid, TRICARE, no insurance, underinsured · source
Good to know: Official pages do not describe a free drug program for Koselugo, and Koselugo is not on the AstraZeneca AZ&Me free-drug list. Patients with Medicare or Medicaid can be connected to third-party resources.
- From a charity · NORD RareCareNeurofibromatosis Type 1 Medical Assistance fundOpen
Pays for: Medical and medication costs.
The foundation says: “Accepting Applications” - From a charity · NORD RareCareNeurofibromatosis Type 1 Premium Copay Assistance fundOpen
Pays for: Insurance premiums and copays.
The foundation says: “Accepting new applications and re-enrollments for current year” - From a charity · The Assistance FundNeurofibromatosis fundOpen
Pays for: Copays, coinsurance, deductibles and other health-related expenses.
The foundation says: “OPEN — Accepting New Patients. TAF is currently accepting new patient enrollments for this program.” - From a charity · TotalAssist (formerly PAN Foundation)Neurofibromatosis fundOpen
Pays for: Out-of-pocket costs for approved medications, up to $6,400 per year. Requires health insurance (any kind).
Clinical trial results
The SPRINT Phase 2 trial in 50 children with NF1 and symptomatic, inoperable plexiform neurofibromas showed a 66% confirmed partial response rate, meaning the majority of patients had measurable tumor shrinkage of at least 20%. Many patients also experienced clinically meaningful improvements in pain, motor function, and disfigurement. The FDA approved it in April 2020 based on these results. Subsequent data confirmed durable responses lasting years in many patients.
Development history
Selumetinib was originally developed by Array BioPharma as ARRY-142886 and later partnered with AstraZeneca. While it was initially studied in various cancers, the NF1 program at the National Cancer Institute demonstrated its remarkable activity in pediatric plexiform neurofibromas. AstraZeneca's rare disease division (now Alexion) brought it to FDA approval in April 2020, making it the first targeted therapy for NF1. The FDA expanded the indication to children aged 1 and older in September 2025 and to adults in November 2025.
Explore Neurofibromatosis Type 1 trials
Other Neurofibromatosis Type 1 treatments
Common questions about Selumetinib
▸What is Selumetinib (Koselugo)?
The first FDA-approved targeted therapy for NF1 plexiform neurofibromas. Selumetinib blocks the RAS/MAPK pathway that becomes overactive when the NF1 gene is mutated, shrinking inoperable tumors in children and adults.
▸How does Selumetinib work?
In NF1, mutations in the NF1 gene remove the brakes on a cell growth pathway called RAS/MAPK. Without the braking protein neurofibromin, this pathway stays constantly active, telling cells to grow and divide unchecked, which leads to tumor formation. Selumetinib works by blocking MEK1 and MEK2, two proteins that sit in the middle of this pathway and relay the growth signal.
By shutting down MEK, selumetinib effectively cuts the wire between the overactive RAS signal and the cell's growth machinery. Tumor cells stop receiving instructions to multiply, and existing tumors can shrink. In the pivotal SPRINT trial, the majority of children saw measurable tumor shrinkage, with many experiencing reduced pain and improved function.
Selumetinib was originally approved for pediatric patients aged 2 and older. Subsequent approvals expanded the indication to children as young as 1 year (September 2025) and to adults (November 2025), broadening access across the NF1 population.
▸What are the side effects of Selumetinib?
The most common side effects in clinical trials were vomiting (most frequent, affecting roughly 80% of patients), diarrhea, nausea, rash and other skin reactions, abdominal pain, and musculoskeletal pain. Selumetinib can also cause eye problems including blurred vision and retinal issues, which require regular ophthalmologic monitoring. Heart function changes (decreased ejection fraction) have been reported and are monitored with periodic echocardiograms. Koselugo can raise the muscle enzyme CPK and can cause serious muscle breakdown (rhabdomyolysis), so CPK is checked before and during treatment; report muscle pain or weakness. Koselugo capsules contain vitamin E, so ask your doctor before taking vitamin E supplements, and bleeding risk may be higher with blood thinners or antiplatelet drugs (the oral granules do not contain vitamin E). Koselugo can harm an unborn baby, so patients who can become pregnant, and males with partners who can, should use effective birth control during treatment and for 1 week after the last dose. Most side effects are manageable with dose adjustments or supportive care.
▸How is Selumetinib taken?
Taken twice daily as oral capsules, with or without food, or as oral granules sprinkled on or mixed with a small amount of soft food such as yogurt or fruit puree. The dose is calculated based on body surface area at 25 mg/m² per dose. Capsules should be swallowed whole, not opened or crushed. Treatment continues as long as the patient is benefiting and tolerating the medication.
▸Is Selumetinib FDA approved?
Yes, Selumetinib (Koselugo) is FDA approved (2020) for the treatment of Neurofibromatosis Type 1.
▸What is Koselugo used for?
Koselugo (selumetinib) is an FDA-approved MEK inhibitor used to treat symptomatic, inoperable plexiform neurofibromas in patients with neurofibromatosis type 1 (NF1). It was the first targeted therapy approved for this condition.
▸How effective is selumetinib for NF1 tumors?
In the SPRINT trial, 66% of children with NF1 plexiform neurofibromas experienced measurable tumor shrinkage with selumetinib, along with improvements in pain and physical function.
▸What is the difference between selumetinib and mirdametinib?
Both are MEK inhibitors for NF1 plexiform neurofibromas. Selumetinib (Koselugo) is dosed continuously twice daily, while mirdametinib (Gomekli) uses an intermittent 21-days-on/7-days-off schedule and was the first to include adults in its initial approval.
Sources and references
Every factual claim on this page is drawn from the public sources listed below. Click any reference to open the original document.
- U.S. Food and Drug Administration · April 10, 2020. FDA approves selumetinib for neurofibromatosis type 1 with symptomatic, inoperable plexiform neurofibromas. https://www.fda.gov/drugs/resources-information-approved-drugs/fda-approves-selumetinib-neurofibromatosis-type-1-symptomatic-inoperable-plexiform-neurofibromas
- New England Journal of Medicine · 2020. Selumetinib in Children with Inoperable Plexiform Neurofibromas. https://www.nejm.org/doi/full/10.1056/NEJMoa1912735
- Alexion / AstraZeneca Rare Disease. Alexion OneSource — Koselugo Support Program. https://alexiononesource.com