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Irinotecan (Irinotel) Two Types of Diarrhoea, Two Different Responses

Medically reviewed by Dr. Naresh Gundu, Medical Oncologist, MBBS (Chalmeda Anand Rao Institute of Medical Sciences, Karimnagar) · DNB Internal Medicine (Sir Gangaram Hospital, New Delhi) · DM Medical Oncology (AIIMS) · Last reviewed September 2026

Irinotecan is a chemotherapy drug that causes diarrhoea in a way most other chemotherapy drugs do not — through two completely different mechanisms, at two different times, needing two different responses. Knowing which type you are dealing with is the first and most important step.

Prescription-only medicine.

Irinotecan is a prescription-only medicine administered by intravenous infusion under specialist oncology supervision. It cannot be started, adjusted, or stopped on the basis of anything read online or outside the advice of your treating team. It is not suitable for everyone — see who this is not for below.

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In short

Irinotecan, sold in India as Irinotel, is a chemotherapy drug that causes two distinct types of diarrhoea. Early diarrhoea happens during or just after the infusion and has a different cause from late diarrhoea, which appears days later. Each type needs a different response, and late diarrhoea can become severe quickly.

In detail

What is irinotecan (Irinotel)?

Irinotecan, sold in India as Irinotel, is a chemotherapy drug from the camptothecin family. It works by blocking an enzyme called topoisomerase I, which cancer cells need to copy their DNA and divide.

It is given as an intravenous infusion in a day-care chemotherapy unit. It is most commonly used in colorectal cancer, and your oncologist may combine it with other medicines as part of your regimen.

In detail

Why does irinotecan cause two different types of diarrhoea?

Irinotecan is unusual among chemotherapy drugs in that it causes diarrhoea through two separate mechanisms, at two separate times.

Early diarrhoea happens during the infusion or within the first 24 hours. It is a cholinergic effect — irinotecan temporarily affects the nerve supply to the gut. It often comes with sweating, abdominal cramps, or a runny nose. Your team can manage it at the time.

Late diarrhoea starts more than 24 hours after the infusion, sometimes several days later. It is caused by the active metabolite of irinotecan, called SN-38, directly damaging the lining of the bowel. It can worsen within hours. This is the type that needs you to act on the day it starts — not a wait-and-see approach.

At a glance

What is the difference between early and late diarrhoea?

Early diarrhoea (during or within 24 hours of infusion)A cholinergic effect caused by irinotecan affecting the nerve supply to the gut. Often accompanied by sweating, flushing, or abdominal cramps. Your team can give medicine to manage it at the time. It is not a sign that something is seriously wrong, and it does not predict late diarrhoea.

Late diarrhoea (more than 24 hours after infusion)Caused by SN-38, the active form of irinotecan, directly damaging the bowel lining. It can start days after the infusion and escalate rapidly. This type needs you to act the same day it begins. Follow your team's loperamide instructions and call them even if it seems mild at first.

Eligibility

Who is irinotecan not suitable for?

Irinotecan is not suitable for everyone. People who are generally not candidates include:

People with significantly reduced liver function, particularly markedly raised bilirubin levelsThe drug is processed by the liver, and toxicity becomes unpredictable when liver function is poor
People with a complete or near-complete bowel obstruction
People with active, severe inflammatory bowel disease
People who are pregnant or breastfeeding
People with very low blood counts at the time treatment would start
People whose general fitness is too poor to tolerate chemotherapy

People with a reduced version of the UGT1A1 enzyme (a genetic variant sometimes called *28) are at higher risk of severe toxicity from irinotecan. This does not always mean the drug cannot be used, but it changes how the treatment is planned. Eligibility in every case is decided by an oncologist, not by a general rule.

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In detail

Why does irinotecan cause hair loss?

Irinotecan affects rapidly dividing cells throughout the body, not only cancer cells. Hair follicles divide quickly, which is why hair loss is a common effect.

It typically begins a few weeks after the first infusion and may affect the scalp, eyebrows, eyelashes, and body hair. For most people, hair grows back after treatment ends, though the texture may differ at first.

Hair loss can be one of the most distressing visible effects of treatment. Mention it to your team early — support is available, and it is a recognised part of managing irinotecan treatment.

Step by step

What should I do when late diarrhoea starts?

Start loperamide as your team has directed

Your oncology team will give you specific loperamide instructions before you go home. Follow that plan from the first loose motion that occurs more than 24 hours after your infusion — do not wait to see if it worsens.

Keep drinking fluids steadily

Late diarrhoea causes fluid loss quickly. Sip water, oral rehydration solution, or clear liquids throughout the day. Do not wait until you feel thirsty.

Note what is happening

Track when the diarrhoea started, how often it is occurring, and whether there is blood, mucus, fever, or abdominal pain. This helps your team assess your situation accurately over the phone.

Call your team the same day

Contact your treating team on the day late diarrhoea starts — not at your next scheduled appointment. If there is blood in your stool, you cannot keep fluids down, or you have a fever, go to hospital rather than waiting for a callback.

Question by question

Other things people ask about irinotecan

Can irinotecan lower my resistance to infection?

Yes. Irinotecan can reduce the white blood cell count — a side effect called neutropenia — which makes infections more serious. NCCN and ASCO guidance classifies fever during chemotherapy as an urgent oncology emergency. Any fever that worries you, or a temperature above the threshold your team has given you, needs same-day review. Do not wait overnight. Call your team or go to hospital immediately.

Why did my oncologist ask about a genetic test before starting?

Some people carry a variant of a gene that controls the UGT1A1 enzyme. This enzyme breaks down SN-38, the active form of irinotecan. People with lower UGT1A1 activity have higher levels of the active drug in their body and are at greater risk of severe diarrhoea and low white cell counts. Testing for this variant before starting helps your oncologist choose the safest approach for you specifically.

What about nausea and vomiting?

Nausea and vomiting are common with irinotecan and are usually manageable with the anti-nausea medicines your team prescribes. Nausea typically peaks in the first few days after the infusion. If your anti-nausea medicine is not working, tell your team — there are alternatives, and you should not be managing significant sickness without help.

Are there things I should tell my team before starting?

Tell your oncologist about any existing liver problems, any previous severe diarrhoea on chemotherapy, whether you are pregnant or breastfeeding, and every medicine or supplement you are taking — including herbal preparations and traditional medicines. Some preparations interact with chemotherapy in ways that are not immediately obvious. Your team needs this information to plan your treatment safely.

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Common questions

Frequently asked questions

Is diarrhoea during the infusion a sign that something is going wrong?

No. Diarrhoea during or within the first few hours of an irinotecan infusion is a known cholinergic effect — it happens because the drug temporarily affects the nerve supply to the gut. It is not a sign of a serious reaction, and it does not mean treatment should stop. Your team will recognise it and can give medicine to manage it at the time. Make sure you mention it so it is noted in your record.

How long does late diarrhoea usually last?

Late diarrhoea can last several days. Starting the management your team has given you on the first day it appears gives it the best chance of responding. If it has not improved after a day of treatment, or if it is getting worse, call your team rather than continuing the same approach alone. ASCO guidance treats persistent late diarrhoea as something needing reassessment, not extended home management.

When is diarrhoea a reason to go to hospital rather than call?

Go directly to hospital if there is blood or mucus in your stool, if you cannot keep any fluids down, if you have a fever alongside the diarrhoea, or if it is very severe from the start. These signs mean you may need intravenous fluids or urgent assessment that cannot safely wait. If you cannot reach your team and feel seriously unwell, go to the nearest hospital emergency department.

Will my hair grow back after irinotecan finishes?

For most people, yes. Hair typically begins to regrow some weeks to months after the last treatment. The texture or colour may differ initially — some people find their hair comes back with a different curl or thickness than before. If hair loss is distressing you, mention it to your team. It is a recognised part of treatment and support is available; you do not need to manage it alone.

Can I take an over-the-counter diarrhoea medicine without calling my team?

Use only what your treating team has told you to use, and call them on the day late diarrhoea starts. Late diarrhoea from irinotecan can escalate within hours, and your team needs to know it has started so they can assess whether home management is safe for you at that point. Self-managing without telling them delays the review that keeps the safer options available.

What happens if loperamide does not control the diarrhoea?

Call your team the same day if loperamide is not helping. You may need to be seen so that your fluid levels and blood counts can be checked. In some cases, intravenous fluids are needed. Your team may also review whether the next dose of irinotecan should be adjusted. Reporting early gives them more options — it is much harder to manage diarrhoea that has been uncontrolled for several days.

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