Koselugo (Selumetinib)

Koselugo (selumetinib) is indicated for conditions involving plexiform neurofibromas in neurofibromatosis type 1, targeting the MAPK/ERK signaling pathway.

• Inoperable plexiform neurofibromas in pediatric patients (≥2 years): reduces tumor growth and associated complications.
• Symptomatic plexiform neurofibromas in NF1 patients of any age: helps control disease progression and improve symptoms.
• Unresectable plexiform neurofibromas in NF1 when surgery is not feasible: provides a non‑surgical therapeutic option.

• Selumetinib selectively inhibits the kinases MEK1 and MEK2, key components of the MAPK/ERK cascade. By blocking MEK activity, the drug prevents downstream phosphorylation of ERK proteins, thereby interrupting cellular proliferation signals that drive tumor growth in neurofibromatosis type 1. This targeted inhibition reduces the expansion of plexiform neurofibroma cells while sparing many normal signaling pathways. The inhibition is reversible and dose‑dependent, allowing modulation of pathway activity based on therapeutic needs.

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

Common Side Effects

• Diarrhea: frequent loose stools that may lead to dehydration.
• Nausea: feeling of sickness often accompanied by vomiting.
• Rash: skin irritation or redness, sometimes itchy.
• Fatigue: persistent tiredness affecting daily activities.

Serious or Rare Side Effects

• Retinal pigment epithelial detachment: vision changes requiring ophthalmologic evaluation.
• Interstitial lung disease: breathing difficulties and cough that may need discontinuation.
• Cardiac dysfunction: reduced left ventricular ejection fraction or heart failure signs.

Before initiating Koselugo, several precautions and monitoring measures should be considered.

• Cardiac monitoring: baseline and periodic echocardiograms to detect left ventricular dysfunction.
• Ophthalmologic assessment: regular eye exams to identify retinal changes or visual disturbances.
• Pregnancy and lactation: avoid use in pregnant or breastfeeding women; safety data are lacking.
• Hepatic impairment: dose adjustment may be required in patients with moderate to severe liver dysfunction.
• Drug interactions: avoid concomitant use with strong CYP3A4 inhibitors or inducers without medical supervision.
• Store at below 25 °C: keep tablets in the original container, protect from moisture and light.

Selumetinib can interact with other medicines, influencing its effectiveness or safety.

Major Interactions (Avoid)

• Strong CYP3A4 inhibitors (e.g., ketoconazole, itraconazole): may increase selumetinib exposure and toxicity.
• Strong CYP3A4 inducers (e.g., rifampin, carbamazepine): may reduce drug levels and efficacy.
• Concurrent use with other MEK or MAPK pathway inhibitors: can amplify adverse effects.

Moderate Interactions (Monitor Closely)

• Moderate CYP3A4 inhibitors (e.g., erythromycin, fluconazole): may modestly raise selumetinib concentrations.
• CYP2C19 inhibitors (e.g., omeprazole): potential for altered metabolism.
• Antacids or acid‑reducing agents: may affect absorption; monitor therapeutic response.