Irinotecano Generis (Irinotecan Hydrochloride Trihydrate)

Irinotecan is indicated for several solid‑tumour cancers where topoisomerase I inhibition is a therapeutic strategy.

• Metastatic colorectal cancer: improves overall survival when combined with fluoropyrimidine‑based regimens.
• Advanced colorectal cancer: used after failure of first‑line therapy to achieve tumor response.
• Small cell lung cancer: part of combination protocols for patients with extensive‑stage disease.
• Other solid tumours (off‑label): may be employed in selected cases such as gastric or pancreatic cancer under specialist supervision.

• After intravenous administration, irinotecan is converted by hepatic carboxylesterases to the active metabolite SN‑38. SN‑38 binds to the DNA‑topoisomerase I complex, stabilizing it and preventing relegation of single‑strand DNA breaks during replication. Accumulation of unrepaired DNA damage leads to apoptosis of rapidly dividing tumor cells. The drug’s effect is cell‑cycle independent, allowing activity in both S‑phase and non‑dividing cells, and its potency is influenced by UGT1A1‑mediated glucuronidation, which determines SN‑38 clearance.

Irinotecan may cause a range of adverse reactions, varying from mild to severe, that require monitoring during therapy.

Common Side Effects

• Diarrhea: often severe, may require antidiarrheal medication.
• Neutropenia: reduced white blood cells increasing infection risk.
• Nausea and vomiting: typical chemotherapy‑related symptoms.
• Alopecia: temporary hair loss during treatment.
• Fatigue: generalized tiredness affecting daily activities.
• Mucositis: inflammation of the mouth lining.
• Electrolyte imbalance: low potassium or magnesium.

Serious or Rare Side Effects

• Febrile neutropenia: fever with low neutrophil count, a medical emergency.
• Severe colitis: inflammation of the colon leading to abdominal pain.
• Hepatotoxicity: elevated liver enzymes indicating liver injury.
• Hypersensitivity reactions: rash, bronchospasm, or anaphylaxis.
• Hemorrhagic cystitis: bleeding from the bladder, though uncommon.
• Cardiotoxicity: rare heart function impairment.
• Pulmonary toxicity: interstitial pneumonitis.

Before initiating irinotecan therapy, clinicians should observe several precautionary measures to minimize risks and ensure safe administration.

• Monitor blood counts: perform regular CBC to detect neutropenia and thrombocytopenia.
• Assess liver function: evaluate bilirubin and transaminases as hepatic impairment alters SN‑38 clearance.
• Evaluate UGT1A1 genotype: identify patients with reduced activity who may experience increased toxicity.
• Hydration and antidiarrheal prophylaxis: use intravenous fluids and loperamide to prevent severe diarrhea.
• Avoid concurrent strong CYP3A4 inhibitors: these can raise irinotecan plasma levels.
• Store at 2-8°C: keep refrigerated, protect from light, do not freeze or shake.

Irinotecan interacts with several medicines that can modify its efficacy or toxicity.

Major Interactions (Avoid)

• Strong CYP3A4 inhibitors (e.g., ketoconazole, clarithromycin): markedly increase irinotecan exposure.
• UGT1A1 inhibitors (e.g., atazanavir): reduce SN‑38 metabolism, raising risk of severe neutropenia and diarrhea.
• Anticoagulants (e.g., warfarin): heightened bleeding risk due to mucosal injury.

Moderate Interactions (Monitor Closely)

• Other cytotoxic agents (e.g., oxaliplatin, 5‑FU): additive myelosuppression may require dose adjustments.
• Antidepressants (e.g., SSRIs): potential for increased serotonin syndrome when combined with antiemetics.
• Proton pump inhibitors: may alter gastric pH affecting oral supportive care drugs.
• Diuretics: monitor electrolyte levels as irinotecan‑induced diarrhea can cause imbalances.