Irinotecan Viatris (Irinotecan Hydrochloride Trihydrate)

Irinotecan is a topoisomerase I inhibitor used in the management of colorectal cancer.

• Metastatic colorectal cancer: improves overall survival when combined with fluoropyrimidine‑based chemotherapy.
• Locally advanced colorectal cancer: facilitates tumor shrinkage to enable surgical resection.
• Adjuvant colorectal cancer: reduces risk of disease recurrence after curative surgery.

• Irinotecan is converted intracellularly to its active metabolite SN‑38, which binds to DNA topoisomerase I and stabilizes the enzyme‑DNA complex. This prevents the relegation of single‑strand breaks during DNA replication, leading to accumulation of DNA damage, inhibition of tumor cell proliferation, and ultimately cell death.

Irinotecan may cause a range of adverse reactions that vary in frequency and severity.

Common Side Effects

• Diarrhea: often delayed and may be severe.
• Neutropenia: reduced white blood cell count.
• Nausea and vomiting.
• Fatigue and weakness.
• Alopecia: hair loss.
• Anemia.

Serious or Rare Side Effects

• Febrile neutropenia: infection with fever.
• Severe colitis or intestinal perforation.
• Cholinergic syndrome: sweating, salivation, bronchospasm.
• Allergic reactions: rash, urticaria, anaphylaxis.
• Hepatotoxicity: elevated liver enzymes.
• Cardiotoxicity: rare cardiac events.

Before initiating therapy, clinicians should evaluate patient-specific risk factors and monitor for toxicity.

• Monitor blood counts: perform regular complete blood count assessments.
• Assess liver function: check hepatic enzymes and bilirubin before each cycle.
• Evaluate bowel health: avoid use in patients with recent abdominal surgery or obstruction risk.
• Avoid in patients with known hypersensitivity to irinotecan or its excipients.
• Use antiemetic prophylaxis: administer appropriate anti‑nausea medication prior to infusion.
• Store at controlled room temperature: keep in original container, protect from light and moisture.

Irinotecan can interact with other medicines, altering its efficacy or safety.

Major Interactions (Avoid)

• Strong CYP3A4 inducers (e.g., rifampin): may reduce exposure to SN‑38.
• UGT1A1 inhibitors (e.g., atazanavir): can increase SN‑38 levels and toxicity.
• Anticholinesterase agents (e.g., donepezil): may exacerbate cholinergic syndrome.
• Live vaccines: immunosuppression may reduce vaccine effectiveness.
• Concurrent myelosuppressive chemotherapy: heightened risk of severe bone‑marrow suppression.

Moderate Interactions (Monitor Closely)

• Warfarin: irinotecan may affect INR, requiring closer monitoring.
• Diuretics: electrolyte shifts can influence irinotecan toxicity.
• Nephrotoxic antibiotics (e.g., aminoglycosides): combined renal stress may increase adverse events.