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Koselugo Side Effects

Generic name: selumetinib

Medically reviewed by Last updated on Oct 26, 2022.

Note: This document contains side effect information about selumetinib. Some dosage forms listed on this page may not apply to the brand name Koselugo.

Applies to selumetinib: oral capsule.

Serious side effects of Koselugo

Along with its needed effects, selumetinib (the active ingredient contained in Koselugo) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking selumetinib:

More common

  • Blistering, crusting, irritation, itching, or reddening of the skin
  • blood in urine
  • cracked, dry scaly skin
  • diarrhea
  • fast heartbeat
  • itching, pain, redness, swelling, tenderness, warmth on the skin
  • loosening of the fingernails
  • muscle or bone pain
  • nosebleeds
  • redness or soreness around the fingernails
  • swelling

Less common

  • Blurred vision
  • change in vision
  • difficult or labored breathing
  • dizziness
  • headache
  • nervousness
  • overbright appearance of lights
  • pounding in the ears
  • rapid weight gain
  • seeing flashes or sparks of light
  • seeing floating spots before the eyes, or a veil or curtain across part of your vision
  • slow or fast heartbeat
  • tightness in the chest

Other side effects of Koselugo

Some side effects of selumetinib may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

For Healthcare Professionals

Applies to selumetinib: oral capsule.


Very common (10% or more): Hemoglobin decreased (41%), neutrophils decreased (33%), lymphocytes decreased (20%)

Frequency not reported: Increased vitamin E causing increased bleeding[Ref]


Very common (10% or more): Creatinine phosphokinase (CPK) increased (79%), musculoskeletal pain (e.g., pain in extremity, back pain, neck pain, musculoskeletal pain) (58%)[Ref]


Very common (10% or more): Blurred vision, photophobia, cataracts, and ocular hypertension (15%), visual impairment

Frequency not reported: Retinal vein occlusion (RVO), retinal pigment epithelial detachment (RPED)[Ref]


Very common (10% or more): Albumin decreased (79%), anorexia (22%), increased/decreased potassium (18%), amylase increased (18%), sodium increased (18%), sodium decreased (16%), weight increased[Ref]


Very common (10% or more): Hematuria (22%), proteinuria (22%)[Ref]


Very common (10% or more): AST increased (41%), ALT increased (35%), alkaline phosphatase increased (18%), acute kidney injury[Ref]


Very common (10% or more): Epistaxis (28%), dyspnea (e.g., exertional dyspnea, dyspnea at rest)[Ref]


Very common (10% or more): Fatigue/malaise (56%), pyrexia (56%), edema (e.g., peripheral swelling, edema, localized edema) (20%), edema (e.g., periorbital edema, face edema)[Ref]


The most common adverse reactions (40% or greater) were vomiting, rash (all), abdominal pain, diarrhea, nausea, dry skin, fatigue, musculoskeletal pain, pyrexia, acneiform rash, stomatitis, headache, paronychia, and pruritus.[Ref]

Nervous system

Very common (10% or more): Headache (48%)[Ref]


Very common (10% or more): Cardiomyopathy (decrease in left ventricular ejection fraction [LVEF] greater than or equal to 10% below baseline) (22%), sinus tachycardia (20%), hypertension[Ref]


Very common (10% or more): Rash (e.g., dermatitis acneiform, rash maculopapular, erythema, rash pustular, urticaria, exfoliative rash, rash pruritic, rash erythematous, eczema) (91%), dry skin (60%), rash acneiform (dermatitis acneiform) (50%), paronychia (e.g., paronychia, nail infection) (48%), pruritus (46%), dermatitis (e.g., dermatitis, dermatitis atopic, dermatitis diaper, eczema, seborrheic dermatitis, skin irritation) (36%), hair changes (e.g., alopecia, hair color change) (32%)

Frequency not reported: Palmar-plantar erythrodysesthesia syndrome[Ref]


Very common (10% or more): Vomiting (82%), abdominal pain (76%), diarrhea (70%), nausea (66%), stomatitis (e.g., stomatitis, mouth ulceration) (50%), constipation (34%), lipase increased (32%), dry mouth, GI perforation, colitis, ileus, intestinal obstruction[Ref]


1. "Product Information. Koselugo (selumetinib)." Astra-Zeneca Pharmaceuticals (2020):

Further information

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

Some side effects may not be reported. You may report them to the FDA.