Reviewed on 4/15/2022

What Is Irinotecan and How Does It Work?

Irinotecan is a prescription medicine used as first-line therapy (with 5-fluorouracil and leucovorin) for metastatic colorectal cancer (CRC) and for CRC that has recurred or progressed following initial fluorouracil-based therapy.

  • Irinotecan is available under the following different brand names: Camptosar

What Are Dosages of Irinotecan?

Adult dosage

Injectable solution

Adult dosage


  • Regimen 1 (Weekly): 125 mg/m² IV infusion over 90 minutes on days 1, 8, 15, 22, then 2 weeks off, then repeat  
  • Regimen 2 (Once Every 3 Weeks): 350 mg/sq.meter IV infusion over 30-90 minutes every 3 Weeks

Combination therapy

  • Regimen 1 (6-week cycle with infusional 5-fluorouracil/ leucovorin): 180 mg/m² IV infusion over 30-90 minutes once on days 1, 15, and 29 IV (infuse over 30-90 min), followed by infusion with leucovorin and 5-fluorouracil; next cycle begins on day 43  
  • Regimen 2 (6-week cycle with bolus 5-fluorouracil/ leucovorin): 125 mg/sq.meter on days 1, 8, 15, and 22 (infuse over 90 min), followed by bolus doses of leucovorin and 5-fluorouracil

Dosage Considerations – Should be Given as Follows

  • See “Dosages”


Digestive Disorders: Common Misconceptions See Slideshow

What Are Side Effects Associated with Using Irinotecan?

Common side effects of Irinotecan include:

  • nausea,
  • vomiting,
  • loss of appetite,
  • constipation,
  • cough,
  • drowsiness,
  • mouth sores,
  • weakness,
  • trouble sleeping, and
  • temporary hair loss.

Serious side effects of Irinotecan include:

  • hives,
  • difficulty breathing,
  • swelling of the face, lips, tongue, or throat,
  • pain, redness, or swelling at the injection site or arms or legs,
  • numbness, tingling, burning of arms or legs,
  • back or bloody stools,
  • change in the amount of urine,
  • shortness of breath,
  • cough,
  • chest pain,
  • weakness on one side of the body,
  • trouble speaking,
  • confusion,
  • rash,
  • itching, and
  • severe dizziness.

Rare side effects of Irinotecan include:

  • none 

This is not a complete list of side effects and other serious side effects or health problems that may occur as a result of the use of this drug. Call your doctor for medical advice about serious side effects or adverse reactions. You may report side effects or health problems to FDA at 1-800-FDA-1088.

What Other Drugs Interact with Irinotecan?

If your medical doctor is using this medicine to treat your pain, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor, health care provider, or pharmacist first.

This information does not contain all possible interactions or adverse effects. Visit the RxList Drug Interaction Checker for any drug interactions. Therefore, before using this product, tell your doctor or pharmacist about all the products you use. Keep a list of all your medications with you and share this information with your doctor and pharmacist. Check with your health care professional or doctor for additional medical advice, or if you have health questions or concerns.


What are risk factors for developing colon cancer? See Answer

What Are Warnings and Precautions for Irinotecan?


  • Hypersensitivity to drugs or excipients
  • Contains sorbitol, which is contraindicated in individuals with hereditary fructose intolerance

Effects of drug abuse

  • None

Short-Term Effects

  • See “What Are Side Effects Associated with Using Irinotecan?”

Long-Term Effects

  • See “What Are Side Effects Associated with Using Irinotecan?”


  • Hyperbilirubinemia, elderly, receiving radiation therapy, abdominal/pelvic radiation history
  • Outside of a clinical study, not for use in combination with a regimen of 5-FU/LV administered for 4-5 consecutive days every 4 weeks owing to increased toxicity, including toxic deaths
  • Renal impairment and acute renal failure were reported; usually in patients who became volume depleted from severe vomiting and/or diarrhea
  • Interstitial pulmonary disease (IPD)-like events, including fatalities, have been reported (in combination and as monotherapy) for the treatment of colorectal cancer and other advanced solid tumors
  • Therapy can cause severe myelosuppression; bacterial, viral, and fungal infections have occurred in patients receiving therapy; manage febrile neutropenia promptly with antimicrobial support; interrupt therapy and reduce subsequent doses if necessary
  • The drug is subject to photodegradation, especially in neutral and alkaline solutions
  • Individuals who are homozygous for the UGT1A1*28 allele are at increased risk for neutropenia following initiation of therapy; consider dose reduction by at least 1 level for pts homozygous in the enzyme UDP-glucuronosyl transferase 1A1*28 (UGT1A1*28) variant
  • Avoid pregnancy; can cause fetal harm

Increased risk of neutropenia

  • Studies have shown that individuals who are homozygous for either the UGT1A1*28 or *6 alleles (*28/*28, *6/*6) or who are compound or double heterozygous for the UGT1A1*28 and *6 alleles (*6/*28) are at increased risk for severe or life-threatening neutropenia during treatment
  • These individuals are UGT1A1 poor metabolizers and experience increased systemic exposure to SN-38, an active metabolite of irinotecan. Individuals who are heterozygous for either the UGT1A1*28 or *6 alleles (*1/*28, *1/*6) are intermediate metabolizers and may also have an increased risk of severe or life-threatening neutropenia
  • Consider UGT1A1 genotype testing for the *28 and *6 alleles to determine UGT1A1 metabolizer status
  • When administering therapy consider a reduction in starting dose by at least one level for patients known to be homozygous or compound heterozygous for the UGT1A1*28 and/or *6 alleles (*28/*28, *6/*6, *6/*28)
  • Closely monitor patients with UGT1A1*28 or *6 alleles for neutropenia during and after treatment; the precise dosage reduction in this patient population is not known; subsequent dosage modifications may be required based on individual patient tolerance to treatment

Diarrhea and cholinergic reactions

  • Also, see Black Box Warnings
  • Early diarrhea
    • Occurs during or shortly after infusion
    • Usually transient and infrequently severe; may be accompanied by cholinergic symptoms of rhinitis, increased salivation, miosis, lacrimation, diaphoresis, flushing, and intestinal hyperperistalsis that can cause abdominal cramping
    • Bradycardia may also occur
    • It may be prevented or treated; consider prophylactic or therapeutic administration of atropine 0.25-1 mg IV/SC unless clinically contraindicated
    • These symptoms are expected to occur more frequently with higher irinotecan doses
  • Late diarrhea
    • Generally occurs more than 24 hours after administration
    • Can be life-threatening since it may be prolonged and may lead to dehydration, electrolyte imbalance, or sepsis
    • Grade 3-4 late diarrhea occurred in 23-31% of patients receiving weekly dosing
    • Late diarrhea can be complicated by colitis, ulceration, bleeding, ileus, obstruction, and infection; megacolon and intestinal perforation are also reported
    • Patients should have loperamide readily available to begin treatment for late diarrhea
    • Begin loperamide with the first episode of poorly formed or loose stools, or the earliest onset of bowel movements more frequent than normal
    • Loperamide is not recommended to be used for more than 48 consecutive hours at the higher doses needed for treating irinotecan-induced diarrhea, owing to the risk of paralytic ileus
    • Monitor and replace fluid and electrolytes; use antibiotic support for ileus, fever, or severe neutropenia
    • Delay subsequent irinotecan weekly chemotherapy until pre-treatment bowel function is restored (ie, more than or equal to 24 hours without antidiarrheal medication)

Pregnancy and Lactation

  • Available postmarketing and published data reporting the use in pregnant women, are insufficient and confounded by concomitant use of other cytotoxic drugs, to evaluate for any drug-associated risk for major birth defects, miscarriage, or adverse maternal or fetal outcomes.
  • Verify the pregnancy status in female patients of reproductive potential before initiating therapy


  • Therapy can cause fetal harm when administered to a pregnant woman
  • Females: Advise female patients of reproductive potential to use effective contraception during treatment and for 6 months after the final dose
  • Males: Due to the potential for genotoxicity, advise male patients with female partners of reproductive potential to use condoms during treatment and for 3 months after the final dose


  • Females: Based on postmarketing reports, female fertility may be impaired by treatment; menstrual dysfunction has been reported following administration
  • Males: Based on findings from animal studies, male fertility may be impaired by treatment


  • Irinotecan and its metabolites are present in human milk; there is no information regarding the effects of the drug on the breastfed infant, or milk production; because of the potential for serious adverse reactions from the drug in a breastfed child, advise lactating women not to breastfeed during treatment and for 7 days after the final dose 

Health Solutions From Our Sponsors