A chemotherapy for bowel cancer
Irinotecan
A chemotherapy given by drip, mainly for bowel cancer, where managing diarrhoea is key.
What is Irinotecan?
Irinotecan is a chemotherapy given as a drip into a vein, used mainly for bowel cancer, often alongside other medicines. It works by blocking an enzyme that cancer cells need to copy their DNA, so they cannot divide. Its most important side effect is diarrhoea, which comes in two forms: an early type during or just after the drip (often with cramps, watery eyes and a runny nose, treated with a medicine called atropine), and a delayed type in the days afterwards (treated promptly with loperamide and plenty of fluids). It also lowers blood counts, so a fever must always be reported urgently.
Education and reference only. This is a plain-language guide to Irinotecan — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Irinotecan is a cancer chemotherapy given as an infusion (a drip) into a vein in a chemotherapy unit, as part of a planned course of several cycles. It is used mainly for bowel (colorectal) cancer, often combined with other chemotherapy medicines, and a special long-acting form is used for some pancreatic cancers. Treatment is always started and supervised by a cancer specialist.
How it works
Irinotecan blocks an enzyme called topoisomerase, which cells rely on to untangle and copy their DNA. Without it, cancer cells cannot divide and they die off, slowing or shrinking the cancer. Because healthy cells in the bone marrow and the lining of the gut also rely on dividing, they can be affected, which is why irinotecan lowers blood counts and can cause significant diarrhoea. How a person handles the drug can vary, which is part of why side effects differ from one person to another.
Company & origin
Originated / developed by: Generic (specialist cancer medicine).
A chemotherapy given as a drip in UK cancer units, mainly for bowel cancer, started and supervised by a cancer specialist.
Practical use
How to take Irinotecan
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- It is given by a nurse as a drip into a vein in a chemotherapy unit; you do not take it at home.
- Tell the nurse straight away if you get cramps, watery eyes, a runny nose or diarrhoea during the drip, as this early type is treated with atropine.
- If diarrhoea starts in the days after treatment, take loperamide promptly exactly as your team advised and drink plenty of fluids.
- Ring your chemotherapy helpline if diarrhoea is severe, does not settle, or comes with a fever, as dehydration and infection can become serious.
- Keep your helpline number with you and go to your blood tests before each cycle.
Weighing it up
Advantages & disadvantages of Irinotecan
Advantages
- An effective chemotherapy for bowel cancer, often used in combination with other medicines.
- Both the early and delayed diarrhoea have clear, effective treatments when acted on promptly.
- Given in planned cycles, with blood counts usually recovering between treatments.
Disadvantages
- Can cause significant diarrhoea, both during the drip and in the days afterwards.
- Lowers blood counts, raising the risk of infection, bruising and anaemia.
- Can cause nausea, hair thinning and tiredness, and side effects vary between people.
Practical use
Good to know
Diarrhoea is the side effect to understand most clearly with irinotecan, and there are two distinct types. The early type happens during or within a short time of the drip and often comes with tummy cramps, watery eyes, a runny nose, sweating or dizziness; the nurse treats this with a medicine called atropine, so tell them straight away if you feel it. The delayed type usually starts a day or more after treatment and can be severe; it is vital to start the anti-diarrhoea medicine loperamide promptly as your team has instructed, drink plenty of fluids, and contact your chemotherapy helpline if it does not settle quickly or you cannot keep fluids down, as dehydration can become serious. As with other chemotherapy, irinotecan lowers the white blood cells that fight infection, so a temperature or feeling very unwell — especially if combined with diarrhoea — can mean neutropenic sepsis, a medical emergency; ring your helpline at once. Chemotherapy can affect fertility, so discuss this before starting; avoid pregnancy or fathering a child during treatment, and avoid live vaccines.
Who should not take it / use with caution
- People who have had a serious allergic reaction to irinotecan.
- It is generally not started when blood counts are too low, a serious infection is present, or there is ongoing bowel obstruction or severe diarrhoea, until reviewed.
- It is avoided in pregnancy and breastfeeding, and used with care in significant liver problems.
Monitoring
- Regular blood tests before each cycle to check blood counts and liver function.
- Reviewing how you cope with diarrhoea and whether the anti-diarrhoea plan is working.
- Watching for dehydration and infection, especially when diarrhoea and a fever occur together.
Side effects
- Early diarrhoea during the drip with cramps, watery eyes and a runny nose (treated with atropine).
- Delayed diarrhoea in the days afterwards (treated promptly with loperamide and fluids), which can be severe.
- Low blood counts (raising the risk of infection — report fever urgently), nausea, hair thinning and tiredness.
Key interactions
- Medicines that affect the liver enzymes that handle irinotecan can change its levels, including some anti-epileptics and certain antibiotics.
- Other treatments that lower blood counts or cause diarrhoea add to the risk, so the programme is planned together.
- Live vaccines should be avoided; tell your team about all medicines, including over-the-counter and herbal products such as St John's wort.
Available as: An infusion (drip) into a vein, given in a chemotherapy unit.
Answers
Irinotecan: frequently asked questions
Why are there two kinds of diarrhoea with irinotecan?
An early type can happen during or just after the drip, often with cramps and watery eyes, and is treated with atropine; a delayed type can start a day or more later and is treated promptly with loperamide and fluids.
What should I do if diarrhoea starts at home?
Take the loperamide your team gave you promptly and exactly as instructed, drink plenty of fluids, and ring your chemotherapy helpline if it is severe, does not settle, or comes with a fever.
Why did I get watery eyes and a runny nose during the drip?
These can be part of the early reaction to irinotecan; tell your nurse, as they can give a medicine called atropine to settle it.
What should I do if I get a fever?
Treat it as urgent, especially if you also have diarrhoea, as a low white-cell count makes infection dangerous; ring your chemotherapy helpline straight away at any time.
Will I lose my hair?
Irinotecan can cause hair thinning rather than always complete loss, and it usually recovers after treatment finishes; your team can talk you through what to expect.
The wider class
About Chemotherapy (topoisomerase inhibitor)
Irinotecan belongs to the chemotherapy (topoisomerase inhibitor) class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
Browse by body system
Authoritative sources
- BNF
- NICE CKS
Building a medicines information resource?
We create evidence-led, dose-free drug and formulary references for teams.