Neurofibromatosis type 1 (NF1) is a rare genetic condition that affects how certain nerve cells grow and develop. Children with NF1 can have small growths on or under the skin called neurofibromas.
Some children also develop larger growths known as plexiform neurofibromas (PN). These are noncancerous tumors that grow along nerves and can cause lumps or changes in appearance, pain, or other problems. Because these tumors often intertwine with healthy tissue, surgery is not always possible.
In 2020, the FDA approved Koselugo (selumetinib) as the first medicine to treat children 2 years and older with NF1 who have PN that cause symptoms and cannot be removed by surgery. In September 2025, the FDA approval was expanded to include children 1 year and older.
Koselugo may also be used for other conditions as determined by your health care provider. This article answers common questions about Koselugo for inoperable PN in children with NF1.
How Is Koselugo Taken?
Your health care provider will calculate the dosage of Koselugo that is right for your child. The dose is based on your child’s body surface area (BSA). BSA is calculated using height and weight and is measured in square meters (m2).
Koselugo is usually taken twice a day (one dose in the morning and one dose in the evening). It is available as capsules and granules that are taken by mouth, as follows:
- Koselugo capsules are an option for children who can swallow capsules. Capsules should be swallowed whole. Do not open, chew, or crush them. The capsules can be taken with or without food.
- Koselugo oral granules are used for children who have trouble swallowing pills. The granules come in capsules that you open. Be sure to review the detailed instructions that come with Koselugo oral granules. Here are the basic steps:
- Sprinkle the granules on 1-3 teaspoons of smooth yogurt or fruit puree made from apples, bananas, pears, or strawberries. (You can puree the fruit yourself or use store-bought ones, such as jars of baby food with these specific fruit purees.)
- The mixture should be swallowed within 30 minutes. If the dose isn’t consumed within 30 minutes, throw away the mixture. This means you should not prepare doses in advance.
- Do not chew or crush the granules, and do not mix them with liquids or other types of foods or fruits besides the types listed above.
- If the granules look clumped or stuck inside the capsule, do not use them and contact your pharmacy for a replacement.
- Throw away the empty capsule shell after use. Do not chew, dissolve, or swallow the capsule shells.
Koselugo is typically continued long term, as long as the medicine is tolerated and the condition is not getting worse. Always follow your health care provider’s instructions carefully and let them know if your child has any trouble taking Koselugo or has side effects. If severe side effects occur, your health care provider may pause treatment and/or lower the dose of Koselugo.
How Was Koselugo Studied?
A study called SPRINT was done to test the effectiveness of Koselugo for treating children with NF1 who have tumors called inoperable PN. Inoperable means the tumor cannot be removed with surgery because of where it is located in the body (for example, when a PN wraps around a vital organ).
To participate in the study, children had to be 2-17 years in age and have a confirmed diagnosis of NF1 with inoperable PN. They also had to have at least one problem caused by a PN, such as visible swelling or lumps (disfigurement), pain, trouble with movement, airway problems, impaired vision, or bladder/bowel problems.
A total of 50 children (30 boys and 20 girls) joined the study. They ranged in age from 3 to 17 years, with a median age of about 10 years (meaning that half were older and half were younger). Most were White (84%), 8% were Black, and 2% were Asian (no other race/ethnicity details were reported). Many children had multiple PN-related health problems. The most common ones were disfigurement (88%), trouble with movement (66%), and pain (52%).
All of the children took Koselugo twice daily. Before starting Koselugo, all of the children had MRI scans to measure their target PN (the inoperable tumor that was causing PN-related problems). The children continued taking Koselugo unless they had severe side effects or their condition got worse.
During treatment, the children had regular exams, including MRI scans, to measure the size (volume) of their target PN. Scans were done approximately every four months for the first two years and then every six months. The main goal was to see how many children had their target PN tumors shrink in volume by at least 20%. Another goal was to see how long the target PN stayed smaller before it started growing again.
What Are the Main Benefits of Koselugo Based on Studies?
The study found that Koselugo was effective for shrinking tumors (inoperable PN) in most children with NF1.
Researchers used specific criteria to measure how children responded to Koselugo.
- To count as a complete response, the target PN tumor had to disappear.
- To count as a partial response, the target PN tumor had to shrink by at least 20% compared with its starting size, and that shrinkage was confirmed on another scan within three to six months.
- A durable response meant the tumor shrinkage lasted for at least 12 months.
The study included a total of 50 children who started taking Koselugo between August 2015 and August 2016. The study is ongoing, and results are being analyzed at different cut-off dates.
As of June 2018, a single National Cancer Institute reviewer who was part of the SPRINT study team evaluated all MRI scans and found that 33 children (66%) had a partial response (tumor shrinkage). No one had a complete response. As far as how long it took to see results, partial responses occurred anywhere from 3.3 months to 1.6 years into treatment, with a median time of 7.2 months. (Median refers to a middle point in a set of results.)
An independent team reviewed the same MRI scans using the same criteria. In their separate analysis of data collected through June 2018, 44% of children had a partial response (meaning there was also an overall response rate of 44%).
As of March 2019, an analysis done by the National Cancer Institute found that 34 children (68%) had a partial response and 28 of these children had a durable response that lasted at least 12 months.
Based on follow-up data from March 2021, some children continued to have tumor shrinkage lasting for at least two or three years while taking Koselugo. Ask your health care provider to learn more about long-term safety and effectiveness of Koselugo. Your results may differ from what was seen in clinical studies.
Are There Additional Potential Benefits of Koselugo Based on Studies?
The study also aimed to see if children had improvement in symptoms such as pain, appearance, and daily functioning. Throughout the study, the kids and their parents completed questionnaires about pain, movement, and other symptoms.
The study found that many children felt better in their daily lives. Half of parents and 38% of children reported that pain interfered less with daily activities. Nearly half of children (48%) and more than half of parents (58%) said their child’s overall quality of life improved. Some children also had improvements in strength (56%) and range of motion (38%).
Every child’s experience with Koselugo can be different. Ask your child’s health care provider what to expect during treatment and how progress will be monitored over time.
Is Koselugo Safe for Children Under 2 Years Old?
In 2020, the FDA first approved Koselugo (selumetinib) to treat children 2 years and older with NF1 who have PN that cause symptoms and cannot be removed by surgery. This approval was for Koselugo capsules, based on the results of the SPRINT study (as described above).
However, many young children have trouble swallowing capsules, and Koselugo capsules should not be opened, chewed, or dissolved. To make treatment possible for these children, the drugmaker developed an oral granule form that can be mixed with a small amount of soft food or fruit puree.
In 2025, the FDA approved Koselugo for children as young as 1 year old with NF1 and PN that cause symptoms and cannot be removed by surgery, based on additional studies showing that the capsule and oral granule forms of Koselugo work the same way in the body. One of the studies looked at the safety of Koselugo oral granules in children ranging from 1 to 7 years (median age 4). The children took Koselugo oral granules for a median of 11 months (ranging from three months to around two years). The side effects seen in this study were similar to those seen in previous studies. In other words, both the oral granules and capsules had the same general safety profile. The FDA also concluded that the treatment benefits seen in older children (ages 2 and up) could be safely extended to children ages 1 year and older.
It is not known if Koselugo is safe or effective for babies under 1 year old.
What Types of Drug Interactions Can Happen With Koselugo?
Some medicines can change how Koselugo works in the body. These interactions may raise the chance of side effects or make Koselugo not work as well.
Certain medicines can increase the amount of Koselugo in the bloodstream, and some increase it more than others. This happens because certain medicines affect how the body breaks down Koselugo. When Koselugo levels get too high, side effects may become more likely and/or more severe. Examples of medicines that cause such interactions are an antibiotic called erythromycin and an antifungal called fluconazole. Health care providers typically avoid prescribing these medicines together. But if one of these medicines must be taken, your child’s provider may lower the Koselugo dose and monitor for side effects more closely.
Grapefruit, grapefruit juice, and Seville oranges may also increase the amount of Koselugo levels in your body. Your child should avoid eating or drinking products with grapefruit, grapefruit juice, or Seville orange (such as jams) while taking Koselugo.
Other medicines can have the opposite effect and decrease the levels of Koselugo in the body. This can make the treatment not work as well. To avoid such interactions, health care providers typically try to choose another medicine that does not interact.
If your child takes Koselugo capsules, you should be aware that one of the ingredients in the capsules is vitamin E. Taking too much vitamin E can increase the risk of bleeding, especially if your child takes another medicine that can increase the risk of bleeding. Your child should not take vitamin E supplements if the total daily amount of vitamin E your child would get (including the amount in Koselugo and any other products) is higher than the safe limit. Vitamin E can be found in many vitamins or supplements over-the-counter (OTC), including some multivitamins. Talk with your child’s health care provider to find out whether the total amount of vitamin E your child is getting is within a safe range.
To help prevent drug interactions, always tell your child’s health care provider about all medicines, vitamins, and supplements your child takes. They can check for possible interactions and adjust treatment if needed.
Is There Any Cost Assistance Available?
A cost assistance program is available from AstraZeneca, the maker of Koselugo. It may reduce the amount you pay. Whether you qualify may depend on what type of insurance you have or if you are uninsured. Visit this website from the drugmaker for more information about Koselugo costs and copay savings. You can also contact the drugmaker at 888-765-4747 to connect with a representative for financial support information and other resources.
