Irinotecan

Colorectal Cancer

Irinotecan is primarily used to treat metastatic cancer of the colon or rectum, which is cancer that has spread to other parts of the body. It is typically used in the following situations:

• First-line therapy: It may be used as an initial treatment for metastatic disease when combined with other chemotherapy medications, such as 5-fluorouracil and leucovorin.
• Recurrent or progressive cancer: It may be used alone for patients whose cancer has returned or worsened after receiving initial treatment with 5-fluorouracil.

  Pancreatic Cancer

  A specific liposomal formulation of irinotecan is used to treat metastatic adenocarcinoma of the pancreas. This treatment is intended for patients who have already received gemcitabine-based chemotherapy and is used in combination with fluorouracil and leucovorin.

  Administration

  Irinotecan is administered as an intravenous (IV) infusion into a vein. It is given by healthcare professionals in a clinical setting, such as a hospital or infusion center.

Mechanism of Action

Irinotecan belongs to a group of medicines called topoisomerase inhibitors. It works by interfering with the genetic material, or DNA, inside cancer cells. For a cancer cell to grow and divide into two new cells, it must first make a copy of its DNA.

The medication targets an enzyme in the body known as topoisomerase I. This enzyme normally helps uncoil and manage DNA during the replication process. When irinotecan blocks this enzyme, it causes the DNA strands to break. These breaks prevent the cell from successfully copying its genetic instructions.

Cell Death

When a cancer cell with damaged DNA tries to divide, the damage becomes permanent. Because the cell cannot repair its DNA or complete the division process, it stops growing and eventually dies. This process helps slow or stop the spread of cancer in the body.

Irinotecan is considered a prodrug, meaning it is converted by the body's own enzymes into a more active form after it is administered. This active form is much more powerful at blocking the topoisomerase enzyme than the original drug itself.

Common Side Effects

• Diarrhea (both early and delayed)
• Nausea and vomiting
• Stomach pain or cramping
• Loss of appetite and weight loss
• Constipation
• Mouth sores
• Feeling weak or tired
• Temporary hair loss
• Dizziness

Serious Side Effects

Seek medical attention immediately if you experience any of the following:

• Severe or persistent diarrhea that does not stop
• Signs of infection, such as fever, chills, or sore throat
• Unusual bruising or bleeding
• Shortness of breath, chest pain, or a new cough
• Signs of an allergic reaction, including hives, swelling of the face or throat, and difficulty breathing
• Symptoms of cholinergic syndrome, such as excessive sweating, watering eyes, runny nose, or increased saliva
• Dark urine or yellowing of the skin or eyes

Boxed Warnings

Irinotecan has boxed warnings for two serious conditions: severe diarrhea and severe myelosuppression (a significant drop in blood cell counts). Both conditions can be life-threatening.

Severe Diarrhea

Diarrhea may occur at two different times during treatment:

• Early diarrhea: This occurs during or immediately after the infusion. It is often part of a group of symptoms called cholinergic syndrome, which may include sweating, watering eyes, and stomach cramps.
• Late diarrhea: This occurs more than 24 hours after the infusion. It can be prolonged and lead to dangerous dehydration or electrolyte imbalances if not treated quickly with anti-diarrheal medication.

Low White Blood Cell Counts

A drop in white blood cells (neutropenia) can weaken the immune system, making it harder to fight infections. Severe neutropenia can lead to life-threatening infections or sepsis. Healthcare providers monitor blood counts regularly to manage this risk.

Genetic Factors

Patients with a specific genetic variation known as the UGT1A1*28 allele are at an increased risk for severe neutropenia. Testing for this variation may help determine the appropriate starting dose.

Lung and Liver Issues

Irinotecan has been associated with interstitial lung disease, a condition that causes scarring of the lungs. Additionally, patients with liver problems may be at a higher risk for side effects and require careful monitoring.

Pregnancy and Fetal Risk

This medication can cause harm to an unborn baby. It is important to use effective birth control during treatment and for a specified time after the last dose. Breastfeeding is not recommended during treatment.

Pregnancy

Irinotecan can cause harm to an unborn baby if used during pregnancy. It is important to inform your healthcare provider if you are pregnant or planning to become pregnant before starting treatment. If pregnancy occurs while using this medication, contact your doctor immediately.

To prevent pregnancy during and after treatment, the following measures are generally recommended:

• For women: Use effective contraception during treatment and for 6 months after the last dose.
• For men: Use effective contraception if your partner can become pregnant during treatment and for 3 months after the last dose.

Breastfeeding

It is unknown if irinotecan passes into breast milk. Because of the potential for serious adverse reactions in a nursing infant, breastfeeding is not recommended during treatment and for at least 7 days after the final dose. Discuss the risks and benefits with your healthcare provider.

Available Forms

Irinotecan is provided as a concentrated liquid solution that requires dilution before it is administered. It is given by a healthcare professional as an intravenous infusion.

There are two primary types of this medication:

• Irinotecan hydrochloride injection: The standard liquid formulation for intravenous use.
• Irinotecan liposome injection: A formulation where the active drug is contained within liposomes (small fat-like particles) for intravenous infusion.

FDA Approval and Indications

Irinotecan is an FDA-approved antineoplastic agent. It is primarily indicated for the treatment of metastatic colorectal cancer, either as a first-line therapy in combination with other medications or as a single agent for patients whose disease has progressed after initial treatment. Additionally, a liposomal formulation of irinotecan is approved for the treatment of metastatic pancreatic adenocarcinoma.

Boxed Warnings

The FDA requires a boxed warning for irinotecan due to the potential for severe, life-threatening complications:

• Diarrhea: Irinotecan can cause both early-onset and late-onset diarrhea. Late-onset diarrhea can be severe and lead to dehydration, electrolyte imbalances, or sepsis.
• Myelosuppression: The drug may cause significant bone marrow suppression, specifically severe neutropenia, which can lead to serious infections.

Due to these risks, the FDA specifies that irinotecan should be administered only under the supervision of a physician experienced in cancer chemotherapy.

Stopping Irinotecan Treatment

Irinotecan is a chemotherapy medication used to treat certain types of cancer. It does not cause physical dependence, and there is no evidence of a withdrawal syndrome occurring when the medication is stopped. Unlike medications such as opioids or certain sedatives, the body does not develop a physical reliance on irinotecan that would lead to symptoms upon cessation.

While there is no withdrawal process, the decision to stop treatment involves several clinical considerations:

• Disease Progression: Stopping chemotherapy may allow the underlying cancer to grow or spread. The decision to discontinue treatment is typically based on the drug's effectiveness, the completion of a treatment cycle, or the patient's overall health.
• Lingering Side Effects: Some side effects of irinotecan, such as low blood cell counts or digestive issues, may persist for several days or weeks after the final dose. These are toxic effects of the drug itself rather than symptoms of withdrawal.
• Medical Supervision: Patients should not skip doses or stop treatment without consulting their oncologist. If treatment must be stopped due to severe adverse reactions, such as severe diarrhea or infection, a healthcare provider will manage the transition and monitor the patient's recovery.