Irinotecan

Chemotherapy (topoisomerase inhibitor) · Used for: Colorectal cancer

💉 Given by IV or injection · Chemotherapy (topoisomerase inhibitor)

Cliff notes

What it is: Chemotherapy (topoisomerase inhibitor).

How it's given: An IV infusion, usually every 2 weeks as part of FOLFIRI.

How it works: Irinotecan blocks an enzyme (topoisomerase I) cancer cells need to copy their DNA.

Common side effects and what helps at home

Side effect	What can help
Sweating, cramping, watery eyes or runny nose during or right after the infusion	These 'cholinergic' symptoms can come with early diarrhea; your team can give medicine (atropine).
Diarrhea (early and late)	Keep the anti-diarrhea medicine your team prescribes at home and follow the plan exactly.
Low blood counts	Hand washing.
Nausea	Anti-nausea medicine.
Hair loss	Common.

Not everyone gets these. Your team may suggest other ways to manage them.

Call your care team now if you have:

Fever of 100.4°F (38°C) or higher, or chills (possible infection when blood counts are low)
Vomiting or diarrhea that won't stop, or you can't keep fluids down
Unusual bleeding or bruising
Shortness of breath or chest pain
Signs of an allergic reaction during or after an infusion: trouble breathing, swelling of the face or throat, hives
Diarrhea along with fever, or more than a few loose stools in a day

Call 911 for trouble breathing, chest pain or signs of stroke.

🗓 What to expect

1️⃣ Before you start

Ask your team for a written schedule and an after-hours phone number.
Bring a list of all your medicines and supplements.

2️⃣ During each infusion

You'll get the medicine through an IV in a clinic; nurses check you during the infusion.
Tell the nurse right away about chills, itching, flushing or trouble breathing.
Bring a snack, water and something to pass the time.

3️⃣ Between doses

Watch for the side effects below and use the checklist.
Keep up with blood tests and visits.
Call your team for anything in the red box.

✅ Side-effect checklist

Print this and check off what you notice so you can tell your team.

Side effect	Noticed?	Notes for my team
Sweating, cramping, watery eyes or runny nose during or right after the infusion	☐
Diarrhea (early and late)	☐
Low blood counts	☐
Nausea	☐
Hair loss	☐

Help paying for Irinotecan

Generic chemo has no single manufacturer program, so the copay foundations below are your best bet.

PAN Foundation: Copays and coinsurance, including for people with Medicare, when a disease fund is open.
HealthWell Foundation: Grants for copays, deductibles and premiums when a fund is open.
CancerCare Co-Payment Assistance Foundation: Help with treatment copays for insured people under income limits.
Good Days: Copay help and some travel costs.
NeedyMeds: Free database of assistance programs, open to anyone.

📋 Medicare: Medicare Part B usually covers drugs given by infusion in a doctor's office or hospital outpatient clinic. You typically pay 20% after the Part B deductible. See Medicare and your cancer drugs.

More: Our guide to paying for cancer treatment.

Regimens that include Irinotecan

FOLFIRI

▶ Watch

Watch: How to Prepare for Your First Infusion Treatment (Chemotherapy, Immunotherapy or Targeted Therapy) (Fred Hutch Patient Education)

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❓ Questions to ask your doctor

What is the goal of this treatment for me?
How will we know if it's working?
Which side effects should I call about right away, and what number do I call after hours?
Which medicines, vitamins or supplements should I avoid?
Will this affect my ability to work, drive or care for my family?
What will this cost me, and who can help me with coverage?

Support groups

Fight Colorectal Cancer: Patient guides, advocacy and community
Colorectal Cancer Alliance: Helpline (877-422-2030) and patient navigation
CancerCare: Free counseling, support groups and financial help
Cancer Support Community: Support groups, a helpline and the MyLifeLine online community

Common questions

Why does irinotecan cause diarrhea?

It can cause cramping and sweating during the infusion (early) and diarrhea days later (late). Both are treatable; follow your plan.

📄 The official FDA label for Irinotecan, including its patient information section, is on DailyMed.

Written by the Cancer Side Effects Guide team from FDA labels and leading cancer centers. Not medical advice. · Last updated: October 15, 2026 · How we write

Not medical advice. This page is general information to help you talk with your care team. It can't replace advice from your doctor or nurse. If you have a fever of 100.4°F (38°C) or higher during treatment, or any symptom that worries you, call your care team now. In an emergency, call 911.