Selumetinib

Pronunciation: sel-ue-MET-i-nib
Generic name: selumetinib
Brand name: Koselugo
Dosage form: oral capsule (10 mg, 25 mg), oral granules (5 mg, 7.5 mg)
Drug class: Multikinase inhibitors

Medically reviewed by Carmen Pope, BPharm. Last updated on Sep 15, 2025.

What is selumetinib?

Selumetinib is used to treat neurofibromatosis type 1 (NF1) in children 1 year of age and older who have plexiform neurofibromas that cannot be completely removed by surgery. It is taken orally twice a day as capsules or oral granules.

Selumetinib gained FDA approval on April 10, 2020 under the brand name Koselugo. There is no generic.

How does selumetinib work?

Selumetinib's mechanism of action involves blocking the action of 2 enzymes (MEK1 and 2) involved in signaling pathways for cell growth and division. Clinical trials have shown that this reduces the number, volume, and spread of neurofibroma tumors.

Selumetinib Side Effects

The most common side effects of selumetinib are:

• nausea, vomiting, stomach pain;

• itching;

• dry skin, acne, rash;

• redness around your fingernails;

• feeling weak or tired;

• mouth pain or soreness, swollen gums;

• muscle or bone pain;

• headache; or

• fever.

Diarrhea is a common side effect of this medicine. Tell your doctor right away the first time you have diarrhea while taking selumetinib.

Serious side effects and warnings

Selumetinib may cause the following serious side effects.

Heart problems. Clinical trials have shown that selumetinib can lower the amount of blood pumped by your heart, which is common and can also be severe. Your healthcare provider will do tests before and during treatment with selumetinib to check how well your heart is working. Tell your healthcare provider right away if you get any of the following signs or symptoms:

• persistent coughing or wheezing
• shortness of breath
• swelling of your ankles and feet
• tiredness
• increased heart rate.

Eye problems. Selumetinib can cause eye problems that can lead to blindness. Your healthcare provider will check your vision before and during treatment with selumetinib. Tell your healthcare provider right away if you get any of the following signs or symptoms:

• blurred vision
• loss of vision
• dark spots in your vision (floaters)
• other changes to your vision.

Severe diarrhea. Diarrhea is common with selumetinib and can also be severe. Tell your healthcare provider right away the first time that you get diarrhea during treatment with selumetinib. Your healthcare provider may give you medicine to help control your diarrhea and may tell you to drink more fluids.

Skin rash. Skin rashes are common with selumetinib and can also be severe. Tell your healthcare provider if you get any of the following signs or symptoms:

• a rash that covers a large area of your body
• peeling skin
• blisters.

Muscle problems (rhabdomyolysis). Muscle problems are common with selumetinib and can also be severe. Treatment with selumetinib may increase the level of the enzyme in your blood called creatine phosphokinase (CPK), and this may be a sign of muscle damage. Your healthcare provider should do a blood test to check your blood levels of CPK before you start taking selumetinib and during treatment. Tell your healthcare provider right away if you get any of the following signs or symptoms:

• muscle aches or pain
• muscle spasms and weakness
• dark, reddish urine.

Drug interactions. Tell your healthcare provider if you are taking aspirin, blood thinners, or other medicines to treat blood clots. Selumetinib contains vitamin E, which may increase your risk of bleeding.

Your healthcare provider may change your dose, temporarily stop, or permanently ask you to stop taking selumetinib if you have any of these side effects.

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

Related/similar drugs

Before taking

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

• have heart problems.
• have eye problems.
• have liver problems.
• are pregnant or plan to become pregnant,
• are breastfeeding or plan to breastfeed.

Selumetinib should not be given to a child younger than 1 year old.

Pregnancy

Selumetinib can harm an unborn baby. Your healthcare provider should check to see if you are pregnant before you begin treatment with selumetinib. Females who can become pregnant should use effective birth control (contraception) during treatment with selumetinib and for 1 week after their last dose.

Males with female partners who can become pregnant should use effective birth control (contraception) during treatment with selumetinib and for 1 week after their last dose.

Tell your healthcare provider right away if you become pregnant or think you may be pregnant during treatment with this treatment.

Breastfeeding

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

How do I Take Selumetinib?

Take or give selumetinib (Koselugo) exactly as your healthcare provider tells you to.

• Do not change your dose or stop taking selumetinib unless your healthcare provider tells you to.
• Your healthcare provider will decide on the right dose of selumetinib based on your or your child’s weight or size (body surface area).
• Take or give selumetinib 2 times a day, about 12 hours apart.

Selumetinib (Koselugo) comes in capsules and oral granules.

If your healthcare provider prescribes selumetinib capsules:

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

If your healthcare provider prescribes selumetinib oral granules:

See the Instructions for Use for the instructions on how to prepare and take or give selumetinib oral granules.

• Prepare selumetinib oral granules by carefully opening the capsule and sprinkling all of the oral granules on a small amount (about 1 to 3 teaspoons) of smooth yogurt, or fruit puree containing the following fruits: apple, banana, pear, or strawberry.
• Take or give the selumetinib oral granules and food mixture within 30 minutes of preparing the dose.
• If the prepared dose of selumetinib oral granules and food mixture is not taken or given within 30 minutes, do not take or give the prepared dose. Throw away the mixture and prepare a new dose.
• If part of a dose is taken or given within 30 minutes of preparing, throw away the remainder of the mixture and do not prepare a new dose. Take or give the full dose within 30 minutes next time.
• The selumetinib (Koselugo) oral granules should flow freely. Do not use if the oral granules are clumped or stuck inside the capsule shell. Contact your pharmacy if this happens.
• Throw away the empty capsule shells after use.
• Do not swallow, chew, or dissolve the capsule shells of selumetinib oral granules.
• Do not chew or crush the selumetinib oral granules. Do not add oral granules to liquids.
• Do not mix selumetinib oral granules in grapefruit or any juice, fruit puree, or jam containing Seville orange.

After taking:

If you vomit shortly after taking selumetinib, do not take another dose. Wait until your next scheduled dose time to take the medicine again.

Tell your doctor if you start having loose stools. You may be given anti-diarrhea medicine. Keep using this medicine for as long as your doctor has prescribed.

• Drink plenty of liquids if you have diarrhea.

Selumetinib can cause your heart to pump less blood than normal. Your heart function will need to be checked every 3 to 6 months while you are taking this medicine.

Selumetinib can also cause eye problems that may lead to blindness. You will need frequent vision exams, and your next dose may be delayed based on the results.

Selumetinib Dosing Information for NF1 Treatment

Standard Pediatric Selumetinib Dosing

Usual selumetinib dose for children 1 year and older with NF1:

• 25 mg/m² orally 2 times a day (approximately every 12 hours).
• Continue until disease progression or unacceptable toxicity occurs.

Dosing Adjustments

Moderate liver impairment (Child-Pugh B): Reduce the recommended dosage to 20 mg/m² orally 2 times a day for patients.

Severe liver impairment (Child-Pugh C): The dosage has not been established.

Strong or moderate CYP3A4 inhibitors or fluconazole: Reduce the dosage as per the Prescribing Information instructions.

Missed Dose and Overdose Information

What to do if You Miss a Selumetinib Dose

If you or your child misses a dose of selumetinib capsules or selumetinib oral granules, take or give the dose as soon as you remember, unless the next dose is due within 6 hours. If your scheduled dose is due within 6 hours, skip the dose and take or give the next dose at the regular time. Do not take two doses at one time.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

What to Avoid While Taking Selumetinib

Dietary restrictions:

• Avoid grapefruit or grapefruit juice, and Seville orange during treatment with Koselugo.
• Avoid St. John's wort during treatment.

What other drugs will affect selumetinib?

Tell your healthcare provider about all the medicines you take, including prescription and over-the-counter medicines, vitamins, and herbal supplements. Especially tell your healthcare provider if you are taking aspirin, blood thinners, or other medicines to treat blood clots. Selumetinib contains vitamin E, which may increase your risk of bleeding.

Storage

How to Store Selumetinib Capsules and Granules:

• Store at room temperature between 68°F to 77°F (20°C to 25°C) away from moisture and heat.
• The bottle of selumetinib capsules and granules contains a desiccant packet to reduce moisture. Do not throw away the desiccant packet.
• Keep the capsules and granules in their original bottle. Keep the bottle tightly closed.
• Keep out of the reach of children.

Special Storage Requirements for Selumetinib Oral Granules: 

• Do not store selumetinib oral granules above 86°F (30°C).
  • If the temperature is above 86°F (30°C), store selumetinib oral granules in the refrigerator between 36°F to 46°F (2°C to 8°C).
  • Selumetinib oral granules may clump together or stick to the capsule shell if the medicine gets too hot, and you may not get your full dose.
• Keep Selumetinib oral granules cold in a cooler bag with a cold pack if you need to take them anywhere.

Keep selumetinib and all medicines out of the reach of children.

Selumetinib Ingredients and Manufacturer Information

Selumetinib (Koselugo) Capsules Active and Inactive Ingredients

Active ingredient: selumetinib.

Inactive ingredients: Capsule contains: vitamin E, polyethylene glycol succinate.

10 mg capsule shell contains: hypromellose, carrageenan, potassium chloride, titanium dioxide, carnauba wax, and purified water. The 10 mg capsule printing ink contains: shellac, iron oxide black, propylene glycol, and ammonium hydroxide.

25 mg capsule shell contains: hypromellose, carrageenan, potassium chloride, titanium dioxide, FD&C blue 2, ferric oxide yellow, purified water, carnauba wax, and/or corn starch. The 25 mg printing ink contains: ferric oxide red, ferric oxide yellow, FD&C Blue 2 aluminum lake, carnauba wax, shellac, and glyceryl monooleate. 

Selumetinib (Koselugo) Oral Granules Active and Inactive Ingredients

Active ingredient: selumetinib.

Inactive ingredients (5 mg, 7.5 mg): Uncoated cores contain: glyceryl dibehenate and stearoyl polyoxylglycerides. Granule coatings contain: acetone, hypromellose acetate succinate, and stearic acid.

5 mg Granules:

• Shell contains: ferric oxide yellow, hypromellose, and titanium dioxide.
• Printing ink contains: butyl alcohol, dehydrated alcohol, ferric oxide black, isopropyl alcohol, potassium hydroxide, propylene glycol, purified water, shellac, and strong ammonia solution.

7.5 mg Granules:

• Shell contains: ferric oxide red, hypromellose, and titanium dioxide.
• Printing ink contains: butyl alcohol, dehydrated alcohol, ferric oxide black, isopropyl alcohol, potassium hydroxide, propylene glycol, purified water, shellac, and strong ammonia solution.

Manufacturer

AstraZeneca, a British-Swedish pharmaceutical company headquartered in Cambridge, UK, makes selumetinib under the brand name Koselugo. Some of AstraZeneca's other notable drugs include:

• Tagrisso (osimertinib) for lung cancer
• Calquence (acalabrutinib) for blood cancers
• Lynparza (olaparib) for various cancers
• Farxiga (dapagliflozin) for diabetes and heart failure
• Symbicort (budesonide/formoterol) for asthma and COPD.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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