Irinotecan Viatris (Irinotecan Hydrochloride Trihydrate)

Irinotecan is a topoisomerase I inhibitor employed in chemotherapy for gastrointestinal and lung cancer indications.

• Metastatic colorectal cancer: improves overall survival when used in combination regimens.
• Adjuvant treatment of colon cancer: reduces the risk of disease recurrence after surgical resection.
• Small cell lung cancer (in combination): enhances response rates when combined with other chemotherapeutic agents.

• After intravenous administration, irinotecan is converted by carboxylesterases to the active metabolite SN‑38. SN‑38 binds to the DNA‑topoisomerase I complex, preventing relegation of single‑strand breaks during DNA replication. This leads to accumulation of DNA damage, triggering apoptosis in rapidly dividing cancer cells while sparing most normal tissues.

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

Common Side Effects

• Neutropenia: reduced white blood cell count increasing infection risk.
• Diarrhea: may be severe and require supportive care.
• Nausea and vomiting: often managed with antiemetics.
• Alopecia: temporary hair loss.
• Fatigue: general tiredness during treatment.
• Anemia: decreased red blood cell count.

Serious or Rare Side Effects

• Febrile neutropenia: fever with low neutrophils indicating infection.
• Severe colitis: life‑threatening inflammation of the colon.
• Hypersensitivity reactions: rash, bronchospasm, or anaphylaxis.
• Hepatotoxicity: elevated liver enzymes or liver dysfunction.
• Pulmonary toxicity: interstitial pneumonitis.
• Tumor lysis syndrome: metabolic disturbances from rapid tumor cell death.

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

• Blood count monitoring: perform complete blood counts regularly to detect neutropenia.
• Liver function assessment: evaluate hepatic enzymes before and during treatment.
• Bowel assessment: screen for pre‑existing diarrhea or bowel obstruction.
• Pregnancy avoidance: contraindicated in pregnancy; use effective contraception.
• Dose adjustment: consider reduced dosing in patients with hepatic impairment.
• Store at 2-8°C: keep refrigerated, protect from light, do not freeze or shake.

Irinotecan can interact with other medicines, influencing efficacy or safety.

Major Interactions (Avoid)

• Strong CYP3A4 inhibitors (e.g., ketoconazole): may increase SN‑38 exposure.
• Concurrent myelosuppressive agents: heighten risk of severe neutropenia.
• High‑dose radiation therapy: can exacerbate gastrointestinal toxicity.
• Live vaccines: increased risk of infection due to immunosuppression.
• UGT1A1*28 homozygosity: markedly higher SN‑38 levels, avoid standard dosing.

Moderate Interactions (Monitor Closely)

• CYP3A4 inducers (e.g., rifampin): may reduce drug effectiveness.
• Anticoagulants (e.g., warfarin): monitor coagulation parameters.
• Diuretics: watch for electrolyte imbalances.
• Other antineoplastic agents: adjust dosing to manage overlapping toxicities.
• Antiemetics (e.g., ondansetron): may affect metabolism, monitor for altered SN‑38 levels.