Koselugo

Koselugo (selumetinib) is used to treat neurofibromatosis type 1 (NF1) in adults and children 1 year and older who have symptomatic plexiform neurofibromas (PN) that cannot be completely removed with surgery. Plexiform neurofibromas are noncancerous tumors that grow along nerves and can cause pain, disfigurement, and problems with movement, breathing, or vision.

Koselugo is taken by mouth twice a day. It comes as capsules and as oral granules. The granules are intended for children and for people who have trouble swallowing capsules. Koselugo is dispensed through specialty pharmacies rather than regular retail pharmacies.

Koselugo was the first medicine approved by the US Food and Drug Administration (FDA) to treat NF1 plexiform neurofibromas. It was first approved in April 2020 for children 2 years and older. In September 2025, the FDA expanded approval to include children as young as 1 year, and on November 19, 2025, approval was expanded to adults.

Koselugo is approved to treat neurofibromatosis type 1 (NF1) in adults and children 1 year and older who have plexiform neurofibromas that cause symptoms and cannot be completely removed by surgery.

Take or give Koselugo exactly as your healthcare provider tells you.

• Do not change your dose or stop taking Koselugo unless your healthcare provider tells you to.
• Your healthcare provider will work out the right dose based on your or your child's body size (body surface area).
• Take or give Koselugo 2 times a day, about 12 hours apart.
• If you or your child vomits after a dose, do not take an extra dose. Take the next dose at the usual time.

How do I take Koselugo capsules?

• Take the capsules with or without food.
• Swallow the capsules whole. Do not open, chew, or crush them.
• Tell your healthcare provider if you or your child has trouble swallowing capsules.

How do I take Koselugo oral granules?

• Open the capsule carefully and sprinkle all of the granules onto a small amount (about 1 to 3 teaspoons) of smooth yogurt, or apple, banana, pear, or strawberry puree.
• Take or give the mixture within 30 minutes of preparing it. If it is not taken within 30 minutes, throw it away and prepare a new dose.
• If only part of a dose is taken within 30 minutes, throw away the rest and do not prepare a new dose. Aim to take the full dose within 30 minutes next time.
• The granules should pour freely. Do not use them if they are clumped or stuck inside the capsule. Contact your pharmacy if this happens.
• Do not chew or crush the granules, do not add them to liquids, and do not swallow, chew, or dissolve the empty capsule shells. Throw the empty shells away after use.
• Do not mix the granules with grapefruit, or with any juice, puree, or jam that contains Seville orange.

Follow the Instructions for Use that come with Koselugo oral granules.

What should I do if I miss a dose?

If you or your child misses a dose, take it as soon as you remember, unless the next dose is due within 6 hours. If the next dose is due within 6 hours, skip the missed dose and take the next dose at the usual time.

Avoid the following during treatment with Koselugo:

• St. John's wort
• Grapefruit and grapefruit juice
• Seville oranges, including juice, puree, or jam made with them

Tell your healthcare provider about all the medicines you take, including prescription and over-the-counter medicines, vitamins, and herbal supplements. In particular, tell them if you take:

• Aspirin, other antiplatelet medicines (such as clopidogrel), or blood thinners, because Koselugo capsules may increase the risk of bleeding
• NSAIDs (nonsteroidal anti-inflammatory drugs)
• St. John's wort
• Strong or moderate CYP3A4 inducers, such as rifampin, phenytoin, and carbamazepine. These should be avoided if possible.
• Strong or moderate CYP3A4 inhibitors, such as ketoconazole, clarithromycin, and grapefruit juice. These may require a lower Koselugo dose.
• Fluconazole, which may require a dose adjustment.

This is not a complete list of interactions. Ask your healthcare provider or pharmacist to review your full medicine list.

What should I tell my doctor before taking Koselugo?

Before taking Koselugo, tell your healthcare provider about all of your medical conditions, including if you have:

• Heart problems, such as a weakened heart muscle (cardiomyopathy) or reduced heart function
• Eye problems
• Liver problems
• Plans to become pregnant, or if you are pregnant
• Plans to breastfeed, or if you are breastfeeding

It is not known if Koselugo is safe and effective in children under 1 year of age.

Can I take Koselugo while pregnant or breastfeeding?

Koselugo can harm an unborn baby.

Females who can become pregnant:

• Your healthcare provider will check whether you are pregnant before you start Koselugo.
• Use effective birth control during treatment and for 1 week after your last dose.
• Tell your healthcare provider right away if you become pregnant or think you may be pregnant during treatment.

Males with female partners who can become pregnant should use effective birth control during treatment and for 1 week after the last dose.

It is not known whether Koselugo passes into breast milk. Do not breastfeed during treatment and for 1 week after the last dose. Talk to your healthcare provider about the best way to feed your baby during this time.

What are the common side effects of Koselugo?

The most common side effects in children are:

• Vomiting
• Diarrhea
• Increased blood levels of an enzyme called creatine phosphokinase (CPK)
• Dry skin
• Redness or infection around the nails (paronychia)
• Nausea
• Acne-like skin rash (dermatitis acneiform)
• Fever.

The most common side effects in adults are:

• Skin rash
• Diarrhea
• Acne-like skin rash (dermatitis acneiform).

Tell your doctor right away the first time you get diarrhea while taking Koselugo, because it can become severe.

What are the serious side effects of Koselugo?

Koselugo can cause serious side effects, including:

Heart problems. Koselugo can reduce the amount of blood the heart pumps. Your healthcare provider will check your heart function before and during treatment. Tell them right away if you have a persistent cough or wheezing, shortness of breath, swelling of the ankles and feet, unusual tiredness, or a faster heartbeat.

Eye and vision problems. Koselugo can cause eye problems that, in rare cases, can lead to vision loss. Your vision will be checked before and during treatment. Tell your healthcare provider right away about blurred vision, loss of vision, dark spots or floaters, or any other change in your sight.

Stomach and bowel problems. Koselugo can cause diarrhea, nausea, vomiting, and mouth sores. Diarrhea can be severe. Tell your healthcare provider the first time you get diarrhea so they can advise you about anti-diarrhea medicine and extra fluids.

Severe skin rashes. Koselugo can cause severe rashes. Tell your healthcare provider if you get a rash that covers a large area, blisters, peeling skin, an itchy rash, or acne-like bumps, or if you notice hair thinning or hair loss.

Muscle problems and increased CPK. Koselugo can raise the blood level of an enzyme called creatine phosphokinase (CPK), which can be a sign of muscle damage. In rare cases this can lead to a serious condition called rhabdomyolysis. Your blood CPK will be checked before and during treatment. Tell your healthcare provider right away about muscle aches or pain, muscle weakness or spasms, or dark, reddish urine.

Increased vitamin E and bleeding risk (capsules only). Koselugo capsules contain vitamin E, which at high levels can make it harder for blood to clot. This may raise the risk of bleeding, especially if you also take a blood thinner (such as warfarin) or an antiplatelet medicine (such as aspirin or clopidogrel). Koselugo oral granules do not contain vitamin E. Tell your healthcare provider about all blood thinners, aspirin, and vitamin E supplements you take so your bleeding risk can be monitored.

Your healthcare provider may lower your dose, pause treatment, or stop Koselugo if you have any of these side effects.

These are not all of the possible side effects of Koselugo. Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

Approval in children was based on the Phase II SPRINT Stratum 1 trial (NCT06175637), in which 50 children aged 2 to 18 years with inoperable, symptomatic plexiform neurofibromas received Koselugo. In this study:

• 66% of children (33 of 50) had a confirmed partial response, meaning their tumor shrank by at least 20%. No child had a complete response (full disappearance of the tumor).
• Among those who responded, 79% kept their response for at least 2 years and 64% for at least 3 years.
• The median time to a response was about 7 months.

Approval in adults was based on the Phase III KOMET trial (NCT04924608), which compared Koselugo with placebo in 145 adults with symptomatic, inoperable plexiform neurofibromas. In this study:

• 20% of adults taking Koselugo had a confirmed partial response, compared with 5% of those taking placebo.
• Among adults who responded, 86% kept their response for at least 6 months.
• The median time to a response was about 4 months.

Koselugo (selumetinib) blocks two proteins called MEK1 and MEK2. These proteins are part of a cell signaling chain known as the RAS-RAF-MEK-ERK pathway, which tells cells when to grow and divide. In NF1, this pathway is overactive, which allows tumors to form and grow.

By blocking MEK1 and MEK2, Koselugo lowers the activity of a related protein called ERK. In laboratory and animal studies of NF1-like tumors, this reduced the number of tumors, decreased tumor size, and slowed tumor growth. Koselugo belongs to a group of medicines called kinase inhibitors, and it is sometimes described as a multikinase inhibitor.

What is the usual dose of Koselugo?

• Capsules (adults and children 1 year and older): 25 mg/m² of body surface area, taken twice daily.
• Oral granules (adults and children 1 year and older): a dose equivalent to 25 mg/m², sprinkled onto or mixed with soft food, taken twice daily.

Dose adjustments:

• Moderate liver impairment (Child-Pugh B): reduce to 20 mg/m² twice daily.
• Severe liver impairment (Child-Pugh C): a recommended dose has not been established.
• With strong or moderate CYP3A4 inhibitors or fluconazole: the dose is reduced as described in the prescribing information.

Koselugo is taken until the disease gets worse or side effects become unacceptable. Your healthcare provider will calculate the exact dose based on body surface area.

Capsules: Store at room temperature between 68°F and 77°F (20°C and 25°C). Brief exposure between 59°F and 86°F (15°C and 30°C) is allowed.

Oral granules: Granules are kept refrigerated during shipping and dispensing. After you receive them, you may store them at room temperature between 68°F and 77°F (20°C and 25°C), but do not store them above 86°F (30°C). If the temperature goes above 86°F (30°C), store the granules in the refrigerator between 36°F and 46°F (2°C and 8°C). If you need to carry the granules with you, keep them cold in a cooler bag with a cold pack. Granules that get too hot may clump or stick to the capsule, which can lead to an incomplete dose.

For both forms:

• Keep Koselugo in its original bottle to protect it from light and moisture, and keep the bottle tightly closed.
• Each bottle contains a desiccant packet to reduce moisture. Do not throw the desiccant packet away.
• Keep Koselugo and all medicines out of the reach of children.

Active ingredient: selumetinib

Koselugo capsules inactive ingredients:

• Capsules (10 mg and 25 mg): vitamin E polyethylene glycol succinate
• Capsule shell (10 mg): carnauba wax, carrageenan, hypromellose, potassium chloride, purified water, and titanium dioxide
• Capsule shell (25 mg): carnauba wax and/or corn starch, carrageenan, FD&C blue 2, ferric oxide yellow, hypromellose, potassium chloride, purified water, and titanium dioxide
• Printing ink (10 mg): ammonium hydroxide, iron oxide black, propylene glycol, and shellac
• Printing ink (25 mg): carnauba wax, FD&C blue 2 aluminum lake, ferric oxide red, ferric oxide yellow, glyceryl monooleate, and shellac

Koselugo oral granules inactive ingredients:

• Uncoated cores (5 mg and 7.5 mg): glyceryl dibehenate and stearoyl polyoxylglycerides
• Granule coatings (5 mg and 7.5 mg): acetone, hypromellose acetate succinate, and stearic acid
• Shell (5 mg): ferric oxide yellow, hypromellose, and titanium dioxide
• Shell (7.5 mg): ferric oxide red, hypromellose, and titanium dioxide
• Printing ink (5 mg and 7.5 mg): butyl alcohol, dehydrated alcohol, ferric oxide black, isopropyl alcohol, potassium hydroxide, propylene glycol, purified water, shellac, and strong ammonia solution