Selumetinib (Koselugo)

Pronunciation: sel-yoo-MEH-tin-ib (koh-seh-LOO-goh).

Generic name
selumetinib
Drug class
MEK1/2 (mitogen-activated protein kinase kinase 1/2) inhibitor -- targeted, specialist-initiated oncology-adjacent therapy
Form
Hard capsule (10 mg, 25 mg) and oral granules (lower-strength, for younger children or those unable to swallow capsules)
Route
Oral
Legal status
Prescription-only, specialist-initiated (typically a neurofibromatosis/paediatric oncology or genetics specialist team)

Availability and supply rules vary by country

Trade names by country: United States · United Kingdom · Canada · Australia · New Zealand

Australia: Koselugo (5) · Full directory

What selumetinib is and how it works

Selumetinib (Koselugo) is a targeted oral cancer-pathway medicine (a MEK1/2 inhibitor) used to treat plexiform neurofibromas -- benign but potentially disfiguring or function-limiting tumours that grow along nerves -- in people with neurofibromatosis type 1 (NF1) whose tumours cause symptoms and cannot be removed by surgery. (1) (2) (3)

Koselugo does not carry a US boxed warning, but it does carry several genuinely serious risks that require regular specialist monitoring throughout treatment: heart pumping function (left ventricular ejection fraction) is checked before starting and at intervals; eye examinations are done before starting and periodically, because of a rare but serious risk of a blocked retinal vein; and blood tests check muscle enzyme (CPK) levels. This medicine's exact approval -- including whether it covers adults as well as children, and the exact age range -- genuinely differs between countries, so always confirm with your specialist team whether and how it is available where you live.

Mechanism of action: how selumetinib works

Selumetinib is a reversible, selective inhibitor of mitogen-activated protein kinase kinase 1 and 2 (MEK1/2), enzymes in the RAS/RAF/MEK/ERK signalling pathway. In NF1, loss of the NF1 tumour-suppressor gene leads to overactive RAS signalling; by blocking MEK1/2 downstream of this pathway, selumetinib is thought to reduce the growth signalling driving plexiform neurofibroma progression. (1) (2)

What selumetinib is used for

Symptomatic, inoperable plexiform neurofibromas in neurofibromatosis type 1 (NF1)

Used to treat plexiform neurofibromas that are causing symptoms (such as pain, disfigurement, or problems with movement or organ function) and cannot be fully removed by surgery, in people with NF1. The exact age range covered (children and/or adults) differs by country -- see the country-specific notes below. (1) (2) (3) (4) (5)

Before taking selumetinib

Do not take / not appropriate for

  • Do not take Koselugo if you have a known hypersensitivity to selumetinib or any ingredient in the product. (United Kingdom, European Union) (2)
  • Do not take Koselugo capsules if you have severe liver impairment, or if you are unable or unwilling to swallow the capsules whole. (United Kingdom, European Union) (2)
  • Do not take supplemental vitamin E while on Koselugo capsules (which already contain vitamin E), because of an increased bleeding risk, especially if you also take blood-thinning medicines. (all countries, capsule formulation) (1) (2)

Tell your clinician about

  • Any history of heart problems or reduced heart pumping function.
  • Any history of eye problems, or any new vision changes, blurred vision, or eye pain.
  • Any history of severe or persistent diarrhoea, or other gastrointestinal conditions.
  • Any history of muscle problems, unexplained muscle pain, weakness, or dark urine.
  • If you take blood thinners (anticoagulants) or antiplatelet medicines, especially with the capsule formulation.
  • Whether you are pregnant, planning pregnancy, or breastfeeding, and your and your partner's plans for contraception.
  • All other medicines you take, especially antifungal medicines, certain antibiotics, or medicines that strongly affect liver enzymes (CYP3A4).
(1) (2)

How to take selumetinib

  • Koselugo is prescribed and dosed only by a specialist team experienced in treating NF1, using your body surface area (BSA) to calculate the exact dose.
  • Capsules must be swallowed whole -- they must not be opened, chewed, or dissolved. Oral granules are prepared and given exactly as instructed by your specialist team, for younger children or those who cannot swallow capsules.
  • Do not change your dose or stop taking Koselugo without your specialist's guidance -- dose adjustments are sometimes needed because of side effects or interactions, but only your care team should make that decision.
  • It can be taken with or without food.
(1) (2)

Procedures and treatment changes

Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (2) (3) (4) (5)

Missed dose

Contact your specialist team for guidance if a dose is missed. Do not double up on your own -- your care team will advise on the correct approach for your specific dosing schedule.

Overdose

Seek urgent medical attention if too much Koselugo has been taken, or if severe side effects develop (such as chest pain, sudden vision changes, severe diarrhoea, or severe muscle pain). There is no specific antidote; management is supportive. (2)

Side effects

Side effects and their urgency vary; report severe, persistent, or concerning symptoms.

Vomiting, diarrhoea, and nausea (very common, especially in children).

What to notice: Vomiting, diarrhoea, and nausea (very common, especially in children).

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (2) (1)

Dry skin, acneiform (acne-like) rash, and paronychia (nail-fold inflammation) -- more common in younger children and post-pubertal patients respectively.

What to notice: Dry skin, acneiform (acne-like) rash, and paronychia (nail-fold inflammation) -- more common in younger children and post-pubertal patients respectively.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (2)

Elevated creatine phosphokinase (CPK), a muscle-enzyme blood test finding, usually mild.

What to notice: Elevated creatine phosphokinase (CPK), a muscle-enzyme blood test finding, usually mild.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (2) (1)

Fever (more common in children).

What to notice: Fever (more common in children).

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (1)

Serious warnings

Signs of reduced heart pumping function (left ventricular dysfunction) — high caution

Symptoms: New shortness of breath, unusual tiredness, swelling of the legs/ankles, or a fast or irregular heartbeat.

Action: Contact your specialist team promptly. Heart function (ejection fraction) is checked with an echocardiogram before starting Koselugo and at regular intervals during treatment (roughly every 3 months in the first year), and treatment may be paused, reduced, or stopped depending on severity. (1) (2)

New or worsening eye/vision problems, including possible retinal vein blockage — high caution

Symptoms: Blurred vision, other new vision changes, or eye pain.

Action: Contact your specialist team promptly for an eye examination. Eye checks are done before starting Koselugo and periodically during treatment. If a blocked retinal vein (retinal vein occlusion) is confirmed, Koselugo must be permanently stopped. (1) (2)

Severe or persistent diarrhoea — high caution

Symptoms: Frequent loose or watery stools.

Action: Start an anti-diarrhoeal medicine as soon as the first loose stool occurs, as advised by your specialist team, and contact them promptly if it does not settle -- severe diarrhoea may require pausing or stopping treatment. (1)

Signs of muscle breakdown (rhabdomyolysis) — high caution

Symptoms: Unexplained muscle pain, weakness, or dark (tea-coloured) urine.

Action: Contact your specialist team promptly for a blood test -- creatine phosphokinase (CPK) is checked before starting and periodically during treatment because of this risk. (1) (2)

Increased bleeding risk with the capsule formulation (vitamin E content) — moderate caution

Symptoms: Unusual bruising or bleeding, particularly if also taking blood-thinning or antiplatelet medicines.

Action: Tell your specialist team if you notice unusual bruising or bleeding. Koselugo capsules contain vitamin E; do not take additional vitamin E supplements, and more frequent monitoring may be needed if you take anticoagulants or antiplatelet medicines. This risk does not apply to the oral granule formulation, which does not contain vitamin E. (1) (2)

Risk to an unborn baby (embryo-fetal toxicity) — high caution

Symptoms: Not applicable -- this is a risk of use during pregnancy, not a symptom to watch for.

Action: Koselugo can cause harm to an unborn baby. Effective contraception is required during treatment and for at least 1 week after the last dose, for both females of reproductive potential and males with partners of reproductive potential. Discuss pregnancy planning and contraception with your specialist team before starting. (1) (2)

Interactions

  • Strong or moderate CYP3A4 inhibitors (and fluconazole) can significantly raise selumetinib levels; concomitant use is generally avoided, or the dose is reduced under specialist guidance if unavoidable. (1) (2)
  • Strong CYP3A4 inducers (such as rifampicin, phenytoin, or carbamazepine) can reduce how well Koselugo works and should generally be avoided. (2)
  • May affect blood levels of certain other medicines, including methotrexate, furosemide, digoxin, and fexofenadine -- tell your specialist team about all other medicines you take. (2)
  • Hormonal contraceptives may be less effective while taking Koselugo -- a barrier contraceptive method is recommended in addition. (2)

Pregnancy, breastfeeding, kidney/liver function, age

Pregnancy

Not recommended in pregnancy, or in women of childbearing potential not using effective contraception -- animal studies showed embryonic death, structural defects, and reduced fetal weight. Effective contraception is required during treatment and for at least 1 week afterward for both partners where relevant. (1) (2) (3) (4) (5)

Breastfeeding

Breastfeeding should be discontinued during treatment, since selumetinib passed into milk in animal studies and a risk to the infant cannot be excluded. (1) (2) (3) (4) (5)

Children

Approved for children with NF1 and symptomatic, inoperable plexiform neurofibromas, though the exact minimum age differs by country and formulation (as young as around age 1 for oral granules in some markets, age 2 or 3 for others) -- confirm the specific approved age range with your specialist team. (1) (2) (3) (4) (5)

Elderly

Not specifically studied in people over 65 with NF1-associated plexiform neurofibromas in the sources reviewed. (1) (2) (3) (4) (5)

Hepatic_impairment

No adjustment needed for mild impairment; moderate impairment requires a reduced dose (20 mg/m^2 twice daily); severe impairment is either not established or contraindicated depending on the specific regulatory source. (1) (2) (3) (4) (5)

Renal_impairment

No dose adjustment needed based on kidney function in the sources reviewed. (1) (2) (3) (4) (5)

Source_ids

US-DAILYMED-KOSELUGO-2026,UK-EMC-KOSELUGO-2026 (1) (2) (3) (4) (5)

Monitoring

Before starting

  • Baseline echocardiogram (heart ejection fraction)
  • Baseline comprehensive eye examination
  • Baseline creatine phosphokinase (CPK) blood test
  • Confirmation of negative pregnancy status where relevant
  • Review of all other medicines for CYP3A4 interactions

During treatment

  • Echocardiogram roughly every 3 months during the first year of treatment, then every 6 months.
  • Periodic eye examinations, with prompt assessment for any new visual symptoms.
  • Periodic CPK blood tests.
  • Ongoing assessment for diarrhoea, skin reactions, and bruising/bleeding (especially with the capsule formulation).
(1) (2)

Storage

Store according to the specific product packaging instructions; keep out of reach of children, and follow any special handling instructions provided by the dispensing pharmacy for capsules or granules.

Professional information

Clinician-facing context only, sourced from the current US FDA and UK SmPC labels; verify against the current full label and local regulatory status before prescribing.

United States / United Kingdom / European Union / Canada

Indication: NF1 with symptomatic, inoperable plexiform neurofibromas (paediatric and adult, per country-specific approved age ranges)

Dose summary: 25 mg/m^2 BSA orally twice daily, individualised via a BSA dosing table, max single dose 50 mg; reduce to 20 mg/m^2 twice daily with moderate hepatic impairment or with unavoidable strong/moderate CYP3A4 inhibitor co-administration.

Renal context: No renal dose adjustment required per the sources reviewed. (1) (2)

Australia

Indication: NF1 with symptomatic, inoperable plexiform neurofibromas -- paediatric indication (age 2+) confirmed; adult-indication approval status not confirmed in this research

Dose summary: Not independently re-derived beyond the paediatric BSA-based dosing already described for other markets; confirm current Australian Product Information directly before prescribing.

Renal context: Not independently confirmed for Australia in this research. (5)

Mechanism of action

Hepatic guidance

Contraindicated or dosing not established in severe hepatic impairment depending on the specific regulatory source; dose reduced in moderate impairment.

Overdose note

No specific antidote; manage with supportive care and close monitoring of cardiac, ocular, gastrointestinal, and muscle-enzyme status. (1) (2)

Frequently asked questions

Is Koselugo (selumetinib) available in the US, UK, Europe, Canada, Australia, and New Zealand?

Mostly yes, but with real differences: it is authorised in the US, UK, EU, and Canada for both children and adults with NF1-related plexiform neurofibromas (adult approvals are as recent as 2025-2026). In Australia, it is TGA-approved and PBS-listed for children (age 2 and older); no source confirms an Australian adult-indication approval yet. In New Zealand, no confirmed Medsafe-approved, marketed product or PHARMAC funding decision could be found -- its availability there is unconfirmed rather than assumed. (1) (2) (3) (4) (5)

Does Koselugo have a boxed warning?

No. Koselugo does not carry an FDA boxed warning. It does carry several genuinely serious Warnings and Precautions -- reduced heart pumping function, eye/retinal problems, severe diarrhoea, muscle-enzyme elevation, a capsule-specific vitamin E/bleeding risk, and risk to an unborn baby -- which require regular monitoring throughout treatment. (1) (2)

Why do I need regular heart and eye checks while taking Koselugo?

Koselugo can, in some people, reduce the heart's pumping efficiency (left ventricular ejection fraction) or cause eye problems including a rare but serious blocked retinal vein. Regular echocardiograms and eye examinations are used to catch these problems early, before starting treatment and at intervals during treatment. (1) (2)

What is the mechanism of action of selumetinib?

Selumetinib is a reversible, selective inhibitor of mitogen-activated protein kinase kinase 1 and 2 (MEK1/2), enzymes in the RAS/RAF/MEK/ERK signalling pathway. In NF1, loss of the NF1 tumour-suppressor gene leads to overactive RAS signalling; by blocking MEK1/2 downstream of this pathway, selumetinib is thought to reduce the growth signalling driving plexiform neurofibroma progression. (1) (2)

What is the generic name of Selumetinib (Koselugo)?

The generic name is selumetinib. (1) (2)

What class of drug is selumetinib?

Selumetinib (Koselugo) is classed as: MEK1/2 (mitogen-activated protein kinase kinase 1/2) inhibitor -- targeted, specialist-initiated oncology-adjacent therapy. (1) (2)

References

  1. KOSELUGO (selumetinib) capsules and oral granules -- full prescribing informationU.S. Food and Drug Administration / DailyMed (NIH), full prescribing information, Alexion/AstraZeneca Rare Disease · United States · accessed 2026-07-30 · source 1
  2. Koselugo 25 mg hard capsules -- Summary of Product Characteristics (plus 10 mg capsules, 5 mg and 7.5 mg granules, all confirmed live-licensed on emc)electronic medicines compendium (emc), United Kingdom -- AstraZeneca UK Limited · United Kingdom · accessed 2026-07-30 · source 2
  3. Koselugo (selumetinib) -- EPAR medicine overviewEuropean Medicines Agency (EMA) -- European Public Assessment Report (EPAR) · European Union · accessed 2026-07-30 · source 3
  4. Koselugo (selumetinib) -- Regulatory Decision Summary and Summary Basis of DecisionHealth Canada -- Notice of Compliance / Regulatory Decision Summary · Canada · accessed 2026-07-30 · source 4
  5. AusPAR: Koselugo (selumetinib)Therapeutic Goods Administration (TGA), Australia -- AusPAR (Australian Public Assessment Report) · Australia · accessed 2026-07-30 · source 5
  6. Selumetinib/Koselugo -- New Zealand marketing-authorisation and funding status not confirmed via live searchMedsafe (New Zealand regulator) / PHARMAC -- search attempted, marketing authorisation not confirmed · New Zealand · accessed 2026-07-30 · source 6

Brand names by country

Single-ingredient selumetinib names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.

Priority countries

United States

  • KOSELUGO25 mg, 10 mg, 7.5 mg, 5 mg · astrazeneca pharmaceuticals lp

United Kingdom

  • Koselugo (2)MHRA licensed emc smpc confirmed black triangle monitoring · 10 mg, 25 mg capsules, 5 mg, 7.5 mg granules · AstraZeneca UK Limited

Canada

  • Koselugo (4)Health Canada approved confirmed · 10 mg, 25 mg capsules · AstraZeneca Canada Inc.

Australia

  • Koselugo (5)TGA approved paediatric indication confirmed PBS listed 2024-08-01 adult indication not confirmed · 10 mg, 25 mg capsules · Alexion Pharmaceuticals Australasia Pty Ltd

New Zealand

  • unconfirmed (6)no medsafe data sheet or pharmac funding decision found live search 2026-07-30 · unconfirmed · unconfirmed
View brands in additional countries.

European Union

Koselugo (3)