This is a topoisomerase I inhibitor which inhibits nucleic acid synthesis by interfering with the coiling and uncoiling of DNA during replication.

Indications: metastatic colorectal cancer in combination with fluorouracil and folinic acid or where treatment containing fluorouracil has failed.

Cautions: raised plasma bilirubin concentration.

Contra-indications: chronic inflammatory bowel disease, bowel obstruction; high plasma bilirubin level; female patient should avoid conception for at least 3 months after cessation of treatment.

Side effect: acute cholinergic syndrome (with early diarrhoea) and delayed diarrhoea.