Irinotecan

Dosing for Irinotecan is highly individualized and is calculated based on the patient's Body Surface Area (BSA), measured in square meters (m²). There are two primary dosing schedules used in clinical practice:

• Single-Agent Regimen (Weekly): The typical starting dose is 125 mg/m² administered as an intravenous infusion over 90 minutes. This is usually given on days 1, 8, 15, and 22 of a 6-week cycle, followed by a 2-week rest period.
• Single-Agent Regimen (Once every 3 weeks): The typical starting dose is 350 mg/m² administered as an intravenous infusion over 90 minutes, repeated every 21 days.
• Combination Regimen (FOLFIRI): In combination with 5-fluorouracil and leucovorin, the standard dose is often 180 mg/m² given once every 2 weeks.

Your oncologist may start with a lower dose (e.g., 100 mg/m² or 300 mg/m²) if you have certain risk factors, such as being over the age of 70, having received prior pelvic radiation, or having a known genetic variation (UGT1A1*28 polymorphism) that affects drug metabolism.

Irinotecan is not currently FDA-approved for use in pediatric patients. While it is sometimes used 'off-label' in specialized pediatric oncology settings for certain childhood solid tumors (like neuroblastoma or rhabdomyosarcoma), safety and effectiveness have not been formally established in patients under the age of 18. Dosing in these cases is strictly managed by pediatric oncology specialists and is often based on weight or BSA.

Renal Impairment

There are no specific formal guidelines for dosing Irinotecan in patients with renal (kidney) impairment, as the primary route of elimination is hepatic. However, healthcare providers exercise extreme caution and may monitor kidney function closely, as dehydration from Irinotecan-induced diarrhea can lead to acute kidney injury.

Hepatic Impairment

Since the liver is the primary site for converting Irinotecan to its active form and for its subsequent inactivation, hepatic function is critical. Patients with a total bilirubin level between 1.0 and 2.0 mg/dL have a significantly higher risk of severe neutropenia. Dosing is generally not recommended if the bilirubin is greater than 2.0 mg/dL, or if the patient has significant liver dysfunction (Child-Pugh Class B or C).

Elderly Patients

Patients over the age of 65 (and especially those over 70) are at a higher risk of severe dehydration and electrolyte imbalances due to diarrhea. For the once-every-3-weeks schedule, a reduced starting dose of 300 mg/m² is often recommended for patients aged 70 or older.

Irinotecan must be administered in a clinical setting (hospital or infusion center) by trained medical personnel. It is not available for self-administration at home.

• Preparation: The medication is diluted into an IV bag. It should be inspected for particles or discoloration before use.
• Infusion Time: The standard infusion time is 90 minutes.
• Pre-medication: To prevent nausea and vomiting, your doctor will likely give you anti-nausea medications (such as ondansetron or dexamethasone) before the infusion starts.
• Monitoring: During the infusion, a nurse will monitor your vital signs and check the IV site. If you feel any burning, pain, or swelling at the injection site, tell the nurse immediately, as the drug can damage tissues if it leaks out of the vein (extravasation).
• Storage: Unopened vials are stored at room temperature (68°F to 77°F) and protected from light. Once diluted, the solution is stable for up to 6 hours at room temperature or 24 hours if refrigerated.

Because Irinotecan is administered on a strict clinical schedule, missing a dose can interfere with the effectiveness of the treatment. If you miss an appointment for your infusion, contact your oncology clinic immediately to reschedule. Do not attempt to 'double up' or take any other medications to compensate for a missed dose.

An overdose of Irinotecan is a medical emergency and typically occurs due to a calculation error in the clinical setting. The primary symptoms of overdose are severe, life-threatening neutropenia (low white blood cells) and severe diarrhea. Treatment is supportive, focusing on intensive hydration, electrolyte replacement, and the administration of colony-stimulating factors (like G-CSF) to boost white blood cell production. There is no specific antidote for Irinotecan overdose.

> Important: Follow your healthcare provider's dosing instructions exactly. Do not adjust your treatment schedule without direct medical guidance from your oncology team.

Irinotecan is associated with a high frequency of side effects, some of which require proactive management.

• Diarrhea: This is the most significant side effect. It occurs in two forms: 'early' (during or shortly after the infusion) and 'late' (more than 24 hours after the infusion). Late-onset diarrhea can be severe and lead to life-threatening dehydration.
• Nausea and Vomiting: Most patients experience some degree of nausea. This is usually managed with pre-medications.
• Neutropenia: A decrease in neutrophils (a type of white blood cell), which increases the risk of serious infections. This typically peaks 7 to 10 days after the infusion.
• Alopecia: Hair loss is common but usually reversible after treatment ends.
• Fatigue: A profound sense of tiredness or weakness that does not improve with rest.
• Abdominal Pain: Cramping or discomfort in the stomach area, often associated with diarrhea.
• Anemia: Low red blood cell count, leading to shortness of breath and pale skin.

• Thrombocytopenia: A decrease in blood platelets, which can lead to easy bruising or bleeding.
• Stomatitis: Inflammation or sores in the mouth and throat.
• Increased Liver Enzymes: Temporary elevations in AST, ALT, or bilirubin levels.
• Fever: Even in the absence of infection, some patients develop a low-grade fever following treatment.
• Dizziness: Feeling lightheaded, often linked to dehydration or low blood pressure.

• Interstitial Lung Disease (ILD): A serious condition involving scarring or inflammation of the lung tissue. Symptoms include new or worsening cough and shortness of breath.
• Severe Allergic Reactions: Anaphylaxis, characterized by hives, swelling of the face or throat, and difficulty breathing.
• Renal Failure: Usually secondary to severe dehydration and low blood pressure from diarrhea.
• Thromboembolic Events: An increased risk of blood clots, such as deep vein thrombosis (DVT) or pulmonary embolism.

> Warning: Stop your activities and call your doctor or seek emergency care immediately if you experience any of the following:

• Severe Diarrhea: Having more than 4 to 6 bowel movements over your normal daily amount, or any diarrhea that occurs at night.
• Neutropenic Fever: A temperature of 100.4°F (38.0°C) or higher accompanied by a low white blood cell count. This is a medical emergency.
• Signs of Dehydration: Extreme thirst, dark urine, very dry skin, or feeling like you might pass out.
• Chest Pain or Shortness of Breath: These could indicate a blood clot in the lungs or a heart-related issue.
• Severe Abdominal Pain: Especially if the belly feels hard or tender to the touch.

While most side effects of Irinotecan resolve after the medication is stopped, some patients may experience lasting effects:

• Peripheral Neuropathy: While less common than with drugs like oxaliplatin, some patients report lingering numbness or tingling in the hands and feet.
• Secondary Malignancies: As with many chemotherapy drugs, there is a very small theoretical risk of developing a different type of cancer years later due to DNA damage.
• Liver Damage: Chronic use in combination with other drugs may contribute to 'blue liver syndrome' (sinusoidal obstruction syndrome).

Irinotecan carries two major FDA Black Box Warnings, the highest level of caution for a medication:

1. 1Severe Diarrhea: Irinotecan can cause both early and late forms of diarrhea. Early diarrhea is often accompanied by cholinergic symptoms (sweating, cramping). Late diarrhea (occurring >24 hours after treatment) can be prolonged and lead to life-threatening dehydration, electrolyte imbalances, and sepsis. It must be treated promptly with loperamide at the first sign of a loose stool.
2. 2Myelosuppression: Severe neutropenia can occur. This lowers the body's ability to fight infections. Deaths due to sepsis (a systemic infection) have been reported. Therapy should be temporarily stopped if white blood cell counts fall too low, and doses should be reduced in subsequent cycles.

Report any unusual symptoms, especially changes in bowel habits or signs of infection, to your healthcare provider immediately.

Irinotecan is a high-alert medication that requires strict medical supervision. Patients must be educated on the 'loperamide protocol' for late-onset diarrhea before receiving their first dose. Because this drug can significantly suppress the immune system, patients should avoid contact with people who have active infections and should not receive 'live' vaccines during treatment.

Warning: Diarrhea and Neutropenia

1. 1Diarrhea: Irinotecan can cause severe diarrhea. Early diarrhea (during or shortly after infusion) may be accompanied by cholinergic symptoms (e.g., sweating, abdominal cramping, salivation). Late diarrhea (occurring more than 24 hours after infusion) can be life-threatening and must be treated immediately with high-dose loperamide.
2. 2Neutropenia: Severe bone marrow suppression (myelosuppression), specifically neutropenia, can occur. This increases the risk of fatal infections. Patients with a fever and low white blood cell count require immediate hospitalization and intravenous antibiotics.

• Cholinergic Syndrome: During the infusion, Irinotecan can trigger a 'cholinergic crisis' caused by the inhibition of acetylcholinesterase. Symptoms include runny nose, increased salivation, watery eyes, sweating, flushing, and abdominal cramps. This is usually treated or prevented with an injection of atropine.
• UGT1A1 Genetic Variation: Patients who are 'homozygous' for the UGT1A1*28 allele (often associated with Gilbert’s Syndrome) are at a significantly higher risk of severe neutropenia. The FDA recommends considering a dose reduction for these patients.
• Extravasation Risk: Irinotecan is an irritant. If the IV fluid leaks into the surrounding tissue, it can cause inflammation. The site must be monitored closely during infusion.
• Hepatic Impairment: Patients with liver disease, particularly those with high bilirubin levels, are at a much higher risk of toxicity and require careful dose adjustments.

To ensure safety, your healthcare team will perform the following tests regularly:

• Complete Blood Count (CBC): To monitor white blood cells, red blood cells, and platelets. This is usually done before every dose.
• Liver Function Tests (LFTs): To monitor bilirubin, AST, and ALT levels.
• Electrolytes: To check for imbalances (potassium, magnesium, sodium) caused by diarrhea.
• Physical Assessment: Frequent checks for signs of dehydration or infection.

Irinotecan can cause dizziness, visual disturbances, and profound fatigue within 24 hours of administration. Patients are advised to avoid driving or operating heavy machinery until they are certain the medication is not affecting their alertness.

Alcohol should be avoided or strictly limited during Irinotecan treatment. Alcohol can worsen the nausea and dehydration caused by the drug and may put additional strain on the liver, which is already working hard to metabolize the chemotherapy.

Irinotecan does not cause a 'withdrawal syndrome,' but it is rarely stopped abruptly unless severe toxicity occurs. Usually, treatment continues until the cancer progresses or the side effects become unmanageable. If you must stop treatment, your doctor will monitor you closely for several weeks to ensure your blood counts recover.

> Important: Discuss all your medical conditions, especially any history of liver disease or bowel problems, with your healthcare provider before starting Irinotecan.

Certain drugs should never be used with Irinotecan because they can cause dangerous changes in how the drug is processed:

• St. John’s Wort: This herbal supplement is a potent inducer of the CYP3A4 enzyme. It significantly lowers the concentration of the active metabolite SN-38, making the cancer treatment much less effective. It should be stopped at least two weeks before starting Irinotecan.
• Ketoconazole: This antifungal medication strongly inhibits the enzymes that break down Irinotecan, leading to a massive increase in drug levels and potentially fatal toxicity.

• Strong CYP3A4 Inducers: Medications like phenytoin, phenobarbital, carbamazepine, and rifampin can lower the levels of Irinotecan in the blood. If these must be used, the dose of Irinotecan may need to be increased, or an alternative anticonvulsant (like levetiracetam) should be considered.
• Strong CYP3A4 Inhibitors: Drugs like clarithromycin, indinavir, and itraconazole can increase the risk of severe side effects by slowing the metabolism of the drug.
• UGT1A1 Inhibitors: Medications like atazanavir or gemfibrozil can interfere with the inactivation of the active metabolite SN-38, increasing the risk of severe diarrhea and neutropenia.

• Laxatives: Using laxatives while on Irinotecan can worsen the risk of severe diarrhea. Only use bowel-regulating medications prescribed by your oncology team.
• Diuretics (Water Pills): Drugs like furosemide can worsen the dehydration and electrolyte loss caused by Irinotecan-induced diarrhea.
• Live Vaccines: Because Irinotecan suppresses the immune system, live vaccines (like the MMR or yellow fever vaccine) can cause the actual disease they are meant to prevent. Use only inactivated (killed) vaccines.

• Grapefruit and Grapefruit Juice: Grapefruit inhibits the CYP3A4 enzyme in the gut and liver. This can lead to unpredictably high levels of Irinotecan in the body. Avoid all grapefruit products during treatment.
• High-Fat Meals: While Irinotecan is given intravenously, nutritional status matters. However, there are no specific 'meal' interactions for the IV form. Maintaining hydration is the most critical dietary factor.

• Antioxidants: Some studies suggest that high-dose antioxidants (like Vitamin E or Vitamin C) might interfere with the oxidative damage chemotherapy uses to kill cancer cells. Consult your oncologist before taking any supplements.
• Kava Kava and Valerian: These may increase the dizziness and sedative effects sometimes seen after an Irinotecan infusion.

Irinotecan does not typically interfere with the chemical results of lab tests, but it will significantly alter the values themselves (e.g., lowering white blood cell counts or raising liver enzymes). Always inform any lab technician that you are undergoing chemotherapy.

> Important: Tell your doctor about ALL medications, supplements, and herbal products you are taking, including over-the-counter drugs like aspirin or ibuprofen.

Irinotecan must NEVER be used in the following circumstances:

• Severe Hypersensitivity: If a patient has had a life-threatening allergic reaction to Irinotecan or any of its ingredients (like sorbitol or lactic acid) in the past.
• Severe Hepatic Failure: Specifically, patients with a bilirubin level greater than 3 times the Upper Limit of Normal (ULN). The liver cannot process the drug at this stage, leading to extreme toxicity.
• Severe Bone Marrow Failure: Patients who already have dangerously low blood counts before starting treatment, as Irinotecan will worsen this to a fatal degree.

In these cases, a doctor will perform a careful risk-benefit analysis:

• Gilbert’s Syndrome: These patients have a genetic deficiency in the UGT1A1 enzyme. While they can receive Irinotecan, they require much lower starting doses and intense monitoring for neutropenia.
• Prior Pelvic/Abdominal Radiation: These patients are at a significantly higher risk of severe bowel toxicity and may require lower doses.
• Active Infection: Treatment should generally be delayed until an active infection is fully treated, as Irinotecan will hinder the body's ability to fight the infection.
• Pregnancy: Irinotecan is known to cause fetal harm. It should only be used in pregnant women if the potential benefit justifies the potential risk to the fetus.

There is a potential for cross-sensitivity between Irinotecan and other camptothecin derivatives, such as Topotecan. If you have had a reaction to Topotecan, your doctor will exercise extreme caution when administering Irinotecan.

> Important: Your healthcare provider will evaluate your complete medical history, including genetic factors and prior treatments, before prescribing Irinotecan.

Irinotecan is classified as FDA Pregnancy Category D. This means there is positive evidence of human fetal risk based on adverse reaction data from investigational or marketing experience or studies in humans. In animal studies, Irinotecan caused significant birth defects and fetal death at doses lower than those used in humans.

• Advice: Women of childbearing potential must use highly effective contraception during treatment and for at least 6 months after the final dose. Men with female partners of childbearing potential should use effective contraception during treatment and for 3 months after the final dose.

It is not known whether Irinotecan or its metabolites are excreted in human milk. However, because many drugs are excreted in milk and because of the potential for serious adverse reactions in nursing infants (including cancer-causing potential and immune suppression), breastfeeding is not recommended during treatment. You should wait at least 7 days after your last dose before resuming breastfeeding.

As previously noted, Irinotecan is not FDA-approved for use in children. Clinical trials in pediatric patients have shown that while the drug is processed similarly to adults, the side effect profile—particularly the risk of severe diarrhea—can be more difficult to manage in small children. Use in this population is strictly limited to clinical trials or specialized tertiary care centers.

Patients over the age of 65 are at a significantly higher risk of 'late' diarrhea and severe dehydration. Clinical data shows that the risk of Grade 3 or 4 diarrhea is much higher in the elderly. For the every-3-week dosing schedule, doctors typically start patients aged 70+ at a lower dose of 300 mg/m². Close monitoring of fluid intake and output is essential for older adults.

While the kidneys are not the primary route of elimination, renal function can be compromised by the side effects of Irinotecan. If a patient becomes severely dehydrated from diarrhea, they can develop 'prerenal' azotemia (a buildup of nitrogen waste in the blood). There are no specific dose adjustments for baseline renal impairment, but the drug must be used with caution in those with pre-existing kidney disease.

The liver is the central hub for Irinotecan activity. Patients with elevated bilirubin levels (between 1.0 and 2.0 mg/dL) have a much higher risk of severe neutropenia. If the bilirubin is above 2.0 mg/dL, the drug is generally not recommended. For patients with AST/ALT levels more than 5 times the normal limit, the safety of Irinotecan has not been established.

> Important: Special populations require individualized medical assessment and often more frequent lab monitoring.

Irinotecan is a semi-synthetic derivative of camptothecin. Its primary mechanism of action is the inhibition of topoisomerase I. During DNA replication, this enzyme creates single-strand nicks to relieve torsional strain. Irinotecan's active metabolite, SN-38, binds to the DNA-topoisomerase I complex, preventing the re-ligation of these nicks. This results in the formation of lethal double-strand DNA breaks when the replication fork collides with the stalled complex. This process is S-phase specific, meaning it primarily kills cells that are actively synthesizing new DNA.

The pharmacodynamics of Irinotecan are characterized by a clear dose-response relationship regarding both tumor shrinkage and toxicity. The 'cholinergic' effects (early diarrhea, sweating) are pharmacodynamic responses to the drug's inhibition of acetylcholinesterase. The anti-tumor effect is delayed, as it depends on the cell cycle progression of the tumor cells.

| Parameter | Value |

|---|---|

| Bioavailability | 100% (Intravenous) |

| Protein Binding | 30-68% (Irinotecan); 95% (SN-38) |

| Half-life | 6-12 hours (Irinotecan); 10-20 hours (SN-38) |

| Tmax | End of 90-minute infusion |

| Metabolism | Hepatic (Carboxylesterase to SN-38; UGT1A1 to SN-38G) |

| Excretion | Fecal 64%, Renal 14-37% |

• Molecular Formula: C33H38N4O6 (as the free base)
• Molecular Weight: 677.18 g/mol (as the hydrochloride trihydrate)
• Solubility: Soluble in water and methanol; slightly soluble in ethanol.
• Description: A pale yellow to yellow crystalline powder.

Irinotecan is classified as a Topoisomerase I Inhibitor. It is part of the larger family of antineoplastic agents known as Camptothecins. Other drugs in this class include Topotecan, though Irinotecan is unique due to its prodrug nature and its specific metabolic pathway involving the UGT1A1 enzyme.