Key points
- Irinotecan (Camptosar) is an injectable chemotherapy drug that stops DNA in cancer cells from unwinding and rewinding properly [1].
- It is used with fluorouracil and leucovorin in bowel cancer that has spread, and has helped patients live longer [1, 2, 3].
- It is part of a multi-drug combination that helped people with pancreatic cancer live longer than an older treatment [4, 5].
- The main side effects: diarrhoea (during the infusion or days later) and very low white blood cells [1].
- In some people a gene difference (UGT1A1) raises the risk of severe side effects; your doctor may ask for a test [1].
What is this drug and how does it work?
For physicians
Irinotecan is a derivative of camptothecin. Topoisomerase I creates transient single-strand breaks in DNA to relieve torsional strain. Irinotecan and its active metabolite SN-38 bind the topoisomerase I–DNA complex and prevent religation of these breaks; as a result, double-strand breaks form during DNA replication that the cell cannot repair effectively [1].
Irinotecan is converted in the body by carboxylesterases to SN-38, which is about 1000 times more potent than irinotecan as a topoisomerase I inhibitor. SN-38 is then inactivated (glucuronidated) by the liver enzyme UGT1A1; this is why genetic differences in this enzyme affect toxicity [1].
Which cancers is it used for?
Your doctor may prescribe this drug for:
- Colorectal cancer that has spread [1, 2, 3]
- Pancreatic cancer that has spread [4]
- Pancreatic cancer after surgery [5]
- Locally advanced rectal cancer (cT3 or cT4) [6]
Whether it suits you depends on the type and stage of your cancer and your test results. Details of each use are in the section for doctors.
For physicians
| Cancer | Setting | Key evidence |
|---|---|---|
| Metastatic colorectal cancer | First line, with fluorouracil and leucovorin (FDA label) | Saltz et al: median overall survival 14.8 vs 12.6 months and confirmed response 39% vs 21% compared with fluorouracil and leucovorin [1, 2]. Douillard et al: median overall survival 17.4 vs 14.1 months [3]. |
| Metastatic colorectal cancer | Monotherapy after recurrence or progression on fluorouracil-based therapy (FDA label) | Compared with best supportive care: median overall survival 9.2 vs 6.5 months; compared with infusional fluorouracil: 10.8 vs 8.5 months [1]. |
| Metastatic pancreatic cancer | First line in the FOLFIRINOX regimen for patients with good performance status (outside the FDA label) | ACCORD 11: median overall survival 11.1 vs 6.8 months with gemcitabine (hazard ratio 0.57) [4]. |
| Pancreatic cancer after surgery | Adjuvant modified FOLFIRINOX for 24 weeks (outside the FDA label) | PRODIGE 24: median overall survival 54.4 vs 35.0 months with gemcitabine (hazard ratio 0.64) [5]. |
| Locally advanced rectal cancer (cT3 or cT4) | FOLFIRINOX before chemoradiotherapy and surgery (outside the FDA label) | PRODIGE 23: 3-year disease-free survival 76% vs 69% (hazard ratio 0.69) [6]. |
Uses marked “outside the FDA label” are accepted in clinical guidelines on the basis of phase 3 trials but are not listed in the official drug label.
Liposomal irinotecan is a different product with a different dose, used in a large study in the NALIRIFOX regimen for metastatic pancreatic cancer [7]. The two products must not be confused.
How it is taken and dosing
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Treatment regimens and doses: index4 regimens
Irinotecan is given only as an intravenous infusion (drip) at a treatment centre, usually over 90 minutes [1]. Anti-sickness medicines are given at least 30 minutes before the infusion, and you may also be prescribed anti-sickness medicine for home [1].
Treatment is repeated in cycles and continues for as long as the drug works and side effects are tolerable [1]. A blood test is done before each dose, and if white blood cells or platelets are low or treatment-related diarrhoea has not settled, the infusion is postponed [1].
From the start of treatment, keep loperamide at home as your doctor directs so you can start it at the first sign of late diarrhoea [1]. Do not skip or move any treatment session without arranging it with your doctor, and do not stop treatment on your own.
- Before starting: UGT1A1 genotyping for the *28 and *6 alleles may be considered; in homozygous or compound heterozygous patients (*28/*28, *6/*6, *6/*28), reduce the starting dose by at least one level. Reducing the starting dose by one level may also be considered with prior pelvic or abdominal radiotherapy, performance status 2 or raised bilirubin; no dose is recommended for bilirubin above 2 mg/dL. Do not give strong CYP3A4 or UGT1A1 inhibitors unless there is no alternative; the timing for stopping strong CYP3A4 inducers and inhibitors before starting is in Interactions, pregnancy and precautions [1].
- Premedication and infusion: antiemetics at least 30 minutes before the infusion (in studies: dexamethasone 10 mg with a 5-HT3 antagonist) and antiemetics for home. Cholinergic symptoms/early diarrhoea: atropine 0.25 to 1 mg IV or subcutaneously (preventive or therapeutic). Dilute in 5% dextrose (preferred) or 0.9% saline (0.12 to 2.8 mg/mL) [1]. Outside a trial, do not combine with the 4- to 5-day fluorouracil/leucovorin regimen every 4 weeks [1].
- Liposomal irinotecan: a separate product with a different dose that must not be confused with conventional irinotecan; in NAPOLI 3 the liposomal irinotecan dose in NALIRIFOX was 50 mg/m² [7], whereas the conventional irinotecan dose in FOLFIRINOX was 180 mg/m² [4].
- Late diarrhoea: loperamide from the first loose stool as per the label regimen (doses in Interactions, pregnancy and precautions); fluids and electrolytes; antibiotics for ileus, fever or severe neutropenia [1].
- Starting a new cycle: granulocytes 1500 per µL or more, platelets 100,000 or more and complete resolution of diarrhoea (at least 24 hours without antidiarrhoeals); delay 1 to 2 weeks, and if there is no recovery after 2 weeks, consider stopping treatment [1].
- Dose modification in combination regimens (by the worst toxicity): grade 2 neutropenia during a cycle: reduce one level; grade 3: omit the dose until grade 2 or less, then reduce one level; grade 4: omit until grade 2 or less, then reduce two levels; febrile neutropenia: omit until resolved, then reduce two levels. Grade 2 to 3 diarrhoea: omit until back to baseline, then reduce one level; grade 4: reduce two levels. For mucositis, reduce only the fluorouracil dose [1].
- Dose modification for monotherapy: grade 3 neutropenia or diarrhoea: omit the dose until grade 2 or less, then reduce by 25 mg/m² (weekly) or 50 mg/m² (every 3 weeks) in the next cycle; grade 4 and febrile neutropenia: reduce by 50 mg/m² [1].
- Kidney and liver: use with caution in renal impairment; not recommended in dialysis. In hepatic impairment clearance falls and SN-38 exposure rises; use with caution [1].
- Monitoring: CBC before each dose; neutrophils below 1000 or febrile neutropenia: withhold and reduce later doses. New dyspnoea, cough or fever: withhold until interstitial lung disease is assessed. Anaphylaxis: discontinue [1].
For physicians
Standard dosing (FDA label, metastatic colorectal cancer)
Combination, regimen 1 (bolus fluorouracil/leucovorin)
First line in metastatic colon or rectal cancer
First line in metastatic colon or rectal cancer [1]
Before prescribing: Prescribing notes: premedication, diarrhoea, dose modification and monitoring| Drug | Dose | Route | Schedule |
|---|---|---|---|
| Each cycle | |||
| Irinotecan | 125 mg/m² | IV, 90-minute infusion | Days 1, 8, 15 and 22 |
| Leucovorin | 20 mg/m² | IV bolus | Days 1, 8, 15 and 22, after irinotecan |
| Fluorouracil | 500 mg/m² | IV bolus | Days 1, 8, 15 and 22, after leucovorin |
Dose levels (mg/m²) irinotecan / fluorouracil: starting 125 / 500; level −1 100 / 400; level −2 75 / 300 (leucovorin fixed at 20). After level −2, reductions of about 20% if toxicity continues [1].
Combination, regimen 2 (infusional fluorouracil/leucovorin)
First line in metastatic colon or rectal cancer
First line in metastatic colon or rectal cancer [1]
Before prescribing: Prescribing notes: premedication, diarrhoea, dose modification and monitoring| Drug | Dose | Route | Schedule |
|---|---|---|---|
| Each cycle | |||
| Irinotecan | 180 mg/m² | IV, 90-minute infusion | Days 1, 15 and 29 |
| Leucovorin | 200 mg/m² | 2-hour IV infusion | Days 1, 2, 15, 16, 29 and 30 |
| Fluorouracil (bolus) | 400 mg/m² | IV bolus | Days 1, 2, 15, 16, 29 and 30 |
| Fluorouracil (infusion) | 600 mg/m² | 22-hour IV infusion after the bolus | Days 1, 2, 15, 16, 29 and 30 |
Dose levels irinotecan / fluorouracil bolus / infusion: starting 180 / 400 / 600; level −1 150 / 320 / 480; level −2 120 / 240 / 360 mg/m² (leucovorin fixed at 200) [1].
Monotherapy, regimen 1 (weekly)
Recurrence or progression after fluorouracil-based therapyCycle length: 6 weeks
Recurrence or progression after fluorouracil-based therapy [1]
Before prescribing: Prescribing notes: premedication, diarrhoea, dose modification and monitoring| Drug | Dose | Route | Schedule |
|---|---|---|---|
| Each cycle | |||
| Irinotecan | 125 mg/m² | IV, 90-minute infusion | Days 1, 8, 15 and 22, then 2 weeks of rest |
Dose levels: 125, 100, 75 mg/m²; later doses by tolerance between 50 and 150 mg/m² (steps of 25 to 50). No toxicity in the previous cycle: increase by 25 mg/m² up to a maximum of 150 [1].
Monotherapy, regimen 2 (every 3 weeks)
Recurrence or progression after fluorouracil-based therapyCycle length: Every 3 weeks
Recurrence or progression after fluorouracil-based therapy [1]
Before prescribing: Prescribing notes: premedication, diarrhoea, dose modification and monitoring| Drug | Dose | Route | Schedule |
|---|---|---|---|
| Each cycle | |||
| Irinotecan | 350 mg/m² | IV, 90-minute infusion | Day 1 |
Dose levels: 350, 300, 250 mg/m²; if needed down to 200 in steps of 50 [1].
Doses follow the trial protocol, guideline or official drug label (source given in the notes of each regimen). Before prescribing, check blood counts, renal and hepatic function, drug interactions and the patient’s condition, and adjust the dose according to the drug label.
Side effects
The most common side effects:
- Diarrhoea in most patients; there are two kinds: one during or shortly after the infusion (sometimes with a runny nose, sweating and stomach cramps) and the other from the second day onwards [1].
- Nausea, vomiting, poor appetite and stomach ache [1].
- Weakness and tiredness, hair loss and fever [1].
- Anaemia and low white blood cells, which show up in blood tests [1].
For physicians
The most common clinically important adverse reactions to irinotecan are diarrhoea, nausea, vomiting, neutropenia and alopecia [1]. The table below shows the frequency of adverse reactions in 304 patients with metastatic colorectal cancer who received weekly single-agent irinotecan (after prior fluorouracil), according to the FDA label [1].
| Adverse reaction | All grades | Grade 3 and 4 |
|---|---|---|
| Late diarrhoea (more than 24 hours after the infusion) | 88% | 31% |
| Nausea | 86% | 17% |
| Asthenia | 76% | 12% |
| Vomiting | 67% | 12% |
| Leucopenia | 63% | 28% |
| Alopecia | 60% | — |
| Anaemia | 60% | 7% |
| Abdominal pain or cramping | 57% | 16% |
| Anorexia | 55% | 6% |
| Neutropenia | 54% | 26% |
| Early diarrhoea (within 24 hours of the infusion) | 51% | 8% |
| Fever | 45% | 1% |
Weight loss and constipation were each reported in 30% of patients (grade 3 and 4: 1% and 2% respectively) [1]. On the every-3-weeks schedule, cholinergic symptoms (rhinitis, increased salivation, lacrimation, sweating, flushing and abdominal cramps during or shortly after the infusion) were reported in 47% of patients [1].
Serious side effects
These are less common but serious; tell your team early if you notice any sign of them:
- Late diarrhoea can become dangerous (dehydration or blood infection). At the first loose stool, start the anti-diarrhoea medicine as your doctor directed, drink plenty of fluids, and call straight away if the diarrhoea lasts more than a day or you have a fever [1].
- Infection because of low white blood cells: a temperature of 38 °C or chills [1].
- Some people clear the drug more slowly because of a gene difference and get more severe side effects; your doctor may lower the dose [1].
- An allergic reaction, kidney damage after dehydration, and lung inflammation (a new cough, shortness of breath and fever) [1].
- Harm to an unborn baby [1].
For physicians
Boxed warning – diarrhoea and myelosuppression: irinotecan causes two kinds of diarrhoea [1]:
- Early diarrhoea (during or shortly after the infusion) is usually transient and may come with cholinergic symptoms such as rhinitis, increased salivation, miosis, lacrimation, sweating, flushing, abdominal cramps and bradycardia; these can be prevented or treated with atropine [1].
- Late diarrhoea (usually more than 24 hours after the infusion) can be prolonged and lead to dehydration, electrolyte imbalance or sepsis, and can be life-threatening. Its median time to onset was 5 days on the every-3-weeks schedule and 11 days on the weekly schedule. Complications such as colitis, ulceration, bleeding, ileus, megacolon and bowel perforation have also been reported [1].
Myelosuppression: severe neutropenia and deaths from sepsis have been reported. The risk is higher with prior pelvic or abdominal radiotherapy and in people with high bilirubin or Gilbert syndrome [1].
Reduced UGT1A1 activity: people with the UGT1A1*28/*28, *6/*6 or *6/*28 genotypes are poor metabolisers and at risk of severe or life-threatening neutropenia; heterozygous people (*1/*28 or *1/*6) may also be at higher risk [1].
Other warnings: severe hypersensitivity (anaphylaxis); acute renal failure, usually after dehydration from severe vomiting or diarrhoea; interstitial lung disease (sometimes fatal), presenting with new or worsening dyspnoea, cough and fever; more toxicity and early deaths in patients with performance status 2; and embryo-fetal toxicity [1]. Post-marketing surveillance has also observed ischaemic cardiac events and thromboembolism [1].
When should I call my doctor?
Contact your treatment team straight away if you have [1]:
- Diarrhoea for the first time during treatment, or diarrhoea not controlled by loperamide within 24 hours
- Black or bloody stools
- Signs of dehydration: light-headedness, dizziness or feeling faint
- Being unable to drink fluids because of nausea or vomiting
- Any fever or sign of infection (chills, burning when passing urine, cough with fever)
- New or worsening shortness of breath, cough or fever
- Signs of a severe allergy, such as swelling of the face or throat, widespread hives or difficulty breathing
Interactions, pregnancy and precautions
- Managing late diarrhoea: start loperamide at the first loose stool or when bowel movements become more frequent. One of the regimens in the label: 4 mg at the first episode, then 2 mg every 2 hours until 12 hours without diarrhoea (4 mg every 4 hours at night); taking these doses for more than 48 hours in a row is not recommended because of the risk of ileus. Drink enough fluids, and avoid laxatives and water tablets while you have diarrhoea [1].
- Other medicines: epilepsy medicines (phenytoin, phenobarbital, carbamazepine), tuberculosis drugs (rifampicin, rifabutin) and the herb St John's wort lower the drug level and are best switched to another medicine at least 2 weeks before starting treatment. Antifungal drugs (ketoconazole, itraconazole, voriconazole), the antibiotic clarithromycin, HIV medicines (ritonavir, atazanavir) and the cholesterol drug gemfibrozil raise the level and increase side effects; most should be stopped at least 1 week before treatment [1]. Give your doctor a full list of your medicines and supplements.
- Pregnancy and contraception: women who could become pregnant should use effective contraception for 6 months after the last dose, and men with a partner who could become pregnant should use condoms for 3 months after the last dose. A pregnancy test is done before starting treatment [1].
- Breastfeeding: do not breastfeed during treatment and for 7 days after the last dose [1].
- Fertility: irinotecan may reduce fertility in women and men; if you are planning a family, talk to your doctor before starting treatment [1].
- Older adults and kidney disease: people over 65 are at higher risk of diarrhoea and should be monitored closely; use in dialysis patients is not recommended [1].
- Driving: dizziness or visual disturbance may occur within 24 hours of the infusion [1].
- Radiotherapy: based on limited data, giving irinotecan at the same time as radiotherapy is not recommended [1].
Frequently asked questions
Why does diarrhoea with irinotecan matter so much?
Late diarrhoea can start several days after the infusion and, if not treated early, can lead to dehydration, salt imbalance and blood infection. This is why you should keep loperamide at home and start it at the first loose stool [1].
Is a genetic test needed before treatment?
A blood gene test can identify people who clear the drug more slowly so they can start at a lower dose [1]. Whether to have this test is your doctor's decision.
What do FOLFIRI and FOLFIRINOX mean?
These are the names of combination regimens. In FOLFIRI, irinotecan is given with fluorouracil and leucovorin, which is used for metastatic colorectal cancer [1, 3]. FOLFIRINOX also includes oxaliplatin and has been studied in pancreatic cancer [4].
Will my hair fall out?
Hair loss is common; more than half of patients lost hair [1].
During the infusion I had sweating, a runny nose and stomach cramps; is that normal?
These “cholinergic” symptoms during or shortly after the infusion are common and usually brief. Your doctor can treat them with atropine or prevent them at later sessions; be sure to tell your nurse [1].
Key studies
Show detailsHide
Key studies
7 itemsFOLFIRINOX versus Gemcitabine for Metastatic Pancreatic Cancer
Pancreatic cancer: ESMO Clinical Practice Guideline for diagnosis, treatment and follow-up
Metastatic Pancreatic Cancer: ASCO Guideline Update
NALIRIFOX versus nab-paclitaxel and gemcitabine in treatment-naive patients with metastatic pancreatic ductal adenocarcinoma (NAPOLI 3): a randomised, open-label, phase 3 trial
FOLFIRINOX or Gemcitabine as Adjuvant Therapy for Pancreatic Cancer
Neoadjuvant chemotherapy with FOLFIRINOX and preoperative chemoradiotherapy for patients with locally advanced rectal cancer (UNICANCER-PRODIGE 23): a multicentre, randomised, open-label, phase 3 trial
Pembrolizumab in Microsatellite-Instability-High Advanced Colorectal Cancer
Related cancer types
Treatment regimens (physicians)
References
7 referencesShow all references, 6 with a study cardClose the reference list
Numbers in the text, such as [1], refer to these sources. Sources with a “Study card” button are summarised in the site’s evidence library.
- 1CAMPTOSAR (irinotecan hydrochloride) injection, for intravenous use — Prescribing Information
- 2
- 3
- 4
- 5
- 6Neoadjuvant chemotherapy with FOLFIRINOX and preoperative chemoradiotherapy for patients with locally advanced rectal cancer (UNICANCER-PRODIGE 23): a multicentre, randomised, open-label, phase 3 trial
- 7NALIRIFOX versus nab-paclitaxel and gemcitabine in treatment-naive patients with metastatic pancreatic ductal adenocarcinoma (NAPOLI 3): a randomised, open-label, phase 3 trial
This page is based on reputable scientific sources and was last updated on 27 October 2026. The content of this website is for educational and informational purposes only and does not replace consultation, diagnosis or treatment by a specialist physician. Consult your treating physician about any treatment decision.
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