Irinotecan Hydrochloride

UsesA DNA topoisomerase inhibitor

General DescriptionIrinotecan is available in 100-mg or 5-mL vials for IV administrationand is used in combination with 5-FU and leucovorinas first-line treatment of metastatic colon cancer.The agent may also be used as a single agent in colorectalcancer as a second-line therapy when 5-FU therapy hasfailed. Additional uses include small cell lung cancer,NSCLC, cervical cancer, esophageal cancer, and gastric cancer Irinotecan is 30% to 60% plasma protein bound, whereasthe active metabolite SN-38 is 95% protein bound. Bindingof SN-38 as the lactone stabilizes the material to ring opening.The elimination of the agent occurs primarily in the bilewith a minor amount of renal elimination. The excretion ofactive metabolites or inactive metabolites such as the glucuronideSN-38G, which may be converted back to SN-38 inthe bile, has been associated with severe diarrhea. Irinotecanand SN-38 have half-lives of 8 and 14 hours, respectively.Irinotecan has two dose-limiting toxicities, myelosuppressionand diarrhea. The diarrhea occurs in two forms, earlyand late. The early form occurs within the first 24 hours afteradministration. It has been associated with inhibition ofacetylcholinesterase, which results in increased gut motility.This early phase is also associated with flushing, abdominalpain, and excessive sweating. Atropine can be used to relievethese symptoms but it is not recommended for prophylacticuse unless there has been a prior episode. The late-phasediarrhea occurs after 24 hours and has been associated withthe presence of active material, particularly SN-38 in the gut,and may last 3 to 10 days. The prolonged nature may lead todehydration and electrolyte imbalances. Loperamide therapyis recommended at the first appearance of a loose stool. If thediarrhea persists, additional agents may be used includingantibiotics that decrease β-glucosidase–producing bacteria inthe gut and prevent the overgrowth of pathogenic bacteria.111Other toxicities include emesis and alopecia.