Irinotecan (Specialist drug)

How it works

Its active metabolite SN-38 inhibits topoisomerase I, preventing re-ligation of DNA strand breaks during replication and triggering cell death.

Prescribing in practice

• Severe diarrhoea is the dose-limiting toxicity; early cholinergic diarrhoea responds to an antimuscarinic, while later-onset diarrhoea requires prompt loperamide and fluid management.
• Severe myelosuppression, especially neutropenia, can occur and may be more pronounced in patients with reduced UGT1A1 activity.
• Avoid in significant bowel obstruction and use cautiously with hepatic impairment or hyperbilirubinaemia.

Monitoring

Monitor full blood count before each cycle and assess for diarrhoea, dehydration, infection and hepatic function during treatment.

Counselling the patient

• Start anti-diarrhoeal treatment at the first loose stool and contact the team if diarrhoea is severe or persistent.
• Report fever promptly, as it may indicate a serious infection with low white cells.
• Acute symptoms such as sweating, cramps or watery eyes around the infusion can be treated by staff.

Evidence & guidelines

Irinotecan-based regimens such as FOLFIRI are established standards in metastatic colorectal cancer.