Irinotecan
Say it: eye-rih-noh-TEE-kan · Brand names: Camptosar
Irinotecan is a chemotherapy medicine that stops cancer cells from copying their genes.
What it is
Cells use a protein called topoisomerase 1 to unwind their genetic code (DNA) before copying it. Irinotecan blocks this protein. The DNA breaks and the cancer cell dies.
Often used for
- colon cancer
- rectal cancer
- and sometimes other cancers, such as pancreas and stomach cancer
How you get it
Irinotecan is given through a vein (IV) in a clinic. The infusion takes about 90 minutes. It is often given once every 2 weeks, or once a week, with other medicines. Your schedule may be different.
Common side effects and what helps
- Diarrhea. It can start during the infusion or days later. Keep the diarrhea medicine your team gives you on hand.
- Sweating, watery eyes, runny nose, or belly cramps during the infusion. Tell your nurse, who can give medicine to help.
- Upset stomach or throwing up. Take nausea medicine as your team tells you.
- Feeling tired. Rest and short walks can help.
- Hair loss or thinning. A soft hat or scarf can help.
- Low blood counts. Your team will check your blood often.
- Not feeling hungry. Eat small snacks during the day.
Call your care team right away if you have
- Diarrhea that does not get better with the medicine your team gave you, or lasts more than 24 hours
- A fever of 100.4 degrees Fahrenheit (38 degrees Celsius) or higher
- Dizziness, fainting, or very dark pee (signs of dehydration)
- Black or bloody stools
- Chills, a sore throat, a cough, or burning when you pee (signs of infection)
- Throwing up or diarrhea so bad you cannot keep fluids down
Before you start, tell your team
- If you are pregnant, may become pregnant, or are breastfeeding
- If you have liver problems
- If you know you have a gene change called UGT1A1*28. It can raise side effects.
- If you have had radiation to the belly or pelvis
- All the medicines, vitamins, and herbal products you take, especially St. John's wort
Good to know
- Diarrhea can be serious. Follow your team's plan for diarrhea medicine exactly.
- You will have blood tests before each treatment to check your blood counts.
- Some people have a gene change that makes side effects worse. Your team may test for it.
- Many medicines interact with irinotecan. Do not start any new medicine or herb without asking your team.
Questions to ask
- When and how should I take diarrhea medicine?
- What should I do if diarrhea does not stop?
- Should I be tested for the UGT1A1 gene?
- How often will I get this medicine?
Part of these treatment plans
Side effect guides
Sources
Quick answers
- What is Irinotecan?
- Irinotecan is a chemotherapy medicine that stops cancer cells from copying their genes. Brand names: Camptosar.
- What is Irinotecan used for?
- colon cancer; rectal cancer; and sometimes other cancers, such as pancreas and stomach cancer.
- How is Irinotecan given?
- Irinotecan is given through a vein (IV) in a clinic. The infusion takes about 90 minutes. It is often given once every 2 weeks, or once a week, with other medicines. Your schedule may be different.
- What are the common side effects of Irinotecan?
- Diarrhea. Sweating, watery eyes, runny nose, or belly cramps during the infusion. Upset stomach or throwing up. Feeling tired. Hair loss or thinning. Low blood counts. Not feeling hungry.
- When should I call my care team while taking Irinotecan?
- Diarrhea that does not get better with the medicine your team gave you, or lasts more than 24 hours; A fever of 100.4 degrees Fahrenheit (38 degrees Celsius) or higher; Dizziness, fainting, or very dark pee (signs of dehydration); Black or bloody stools; Chills, a sore throat, a cough, or burning when you pee (signs of infection); Throwing up or diarrhea so bad you cannot keep fluids down.
- Which chemotherapy plans include Irinotecan?
- FOLFIRI, FOLFIRINOX, FOLFOXIRI.
Last updated: 2026-10-27. Medically reviewed by Veli Bakalov, MD, medical oncologist (October 2026). General education from Step by Step, the patient portal of HemeOncBuddy.