Koselugo (Selumetinib)

• Koselugo targets the MAPK/ERK cascade by inhibiting MEK1/2, a key driver of cell proliferation in tumors associated with neurofibromatosis type 1. In patients with inoperable plexiform neurofibromas, the drug is employed to control tumor burden, alleviate symptoms, and improve quality of life.
• Neurofibromatosis type 1 (inoperable plexiform neurofibromas): reduces tumor growth and may shrink existing lesions, helping to manage disease complications.
• Neurofibromatosis type 1 (overall disease progression): may delay the development of new neurofibromas and associated complications.
• Neurofibromatosis type 1 (symptom management): can reduce pain and improve functional mobility in affected patients.

• Selumetinib selectively inhibits the kinases MEK1 and MEK2, which lie downstream of the RAS/RAF/MEK/ERK signaling cascade. By blocking MEK activity, the drug prevents phosphorylation of ERK1/2, halting transcription of genes that drive cell proliferation and survival. This interruption of the MAPK pathway reduces tumor cell growth in neurofibromatosis type 1–associated plexiform neurofibromas. The inhibition is reversible and dose‑dependent, allowing modulation of pathway activity without complete shutdown of normal cellular functions.

Selumetinib may cause a range of adverse reactions, which are categorized by frequency and severity.

Common Side Effects

• Nausea: feeling of queasiness that may lead to vomiting.
• Diarrhea: loose or watery stools.
• Fatigue: persistent tiredness or lack of energy.
• Rash: skin irritation or redness.
• Vomiting: expulsion of stomach contents.
• Edema: swelling due to fluid retention.
• Headache: mild to moderate head pain.

Serious or Rare Side Effects

• Interstitial lung disease: inflammation of lung tissue that can impair breathing.
• Cardiac dysfunction: reduced heart pumping ability or arrhythmias.
• Retinal vein occlusion: blockage of retinal blood vessels affecting vision.
• Severe hypertension: high blood pressure that may lead to organ damage.
• Hepatic toxicity: liver enzyme elevation or hepatitis.
• Severe skin reactions: Stevens‑Johnson syndrome or toxic epidermal necrolysis.

When prescribing Selumetinib, clinicians should observe several precautionary measures to ensure patient safety.

• Cardiac monitoring: baseline and periodic echocardiograms to detect reduced ejection fraction.
• Liver function tests: assess transaminases before treatment and regularly during therapy.
• Ophthalmologic evaluation: perform eye exams to identify retinal changes or visual disturbances.
• Drug hypersensitivity: discontinue if signs of severe allergic reaction such as rash or angioedema occur.
• Concomitant medications: avoid strong CYP3A4 inhibitors or inducers that may alter drug exposure.
• Store below 25°C: keep capsules in the original container, protect from moisture and light.

Selumetinib can interact with other medicines, affecting its plasma levels or increasing toxicity.

Major Interactions (Avoid)

• Strong CYP3A4 inhibitors (e.g., ketoconazole, itraconazole): may raise selumetinib concentrations.
• Strong CYP3A4 inducers (e.g., rifampin, carbamazepine): may lower selumetinib exposure.
• Other MEK inhibitors: combined pathway inhibition can increase adverse events.
• QT‑prolonging agents: additive risk of cardiac arrhythmias.
• Antacids containing aluminum or magnesium: may reduce absorption if taken simultaneously.

Moderate Interactions (Monitor Closely)

• Warfarin: potential alteration of anticoagulant effect, monitor INR.
• Statins (e.g., simvastatin): increased risk of myopathy, consider dose adjustment.
• Oral contraceptives: possible reduced efficacy, advise alternative contraception.
• Antihypertensives: monitor blood pressure for additive effects.
• Diuretics: watch for electrolyte disturbances.