Irinotecan Actavis: Uses, Dosage & Side Effects

What Is Irinotecan Actavis and What Is It Used For?

Irinotecan Actavis contains the active substance irinotecan hydrochloride trihydrate at a concentration of 20 mg/ml. Irinotecan belongs to the pharmacological class of topoisomerase I inhibitors and is a semisynthetic derivative of camptothecin, a naturally occurring alkaloid originally isolated from the bark and stem of Camptotheca acuminata, a tree native to China. The development of irinotecan represented a major milestone in cancer pharmacology, as it introduced a novel mechanism of action distinct from the DNA-damaging and antimetabolite agents that dominated chemotherapy for decades.

The mechanism of action of irinotecan is both elegant and complex. Irinotecan itself functions as a prodrug, meaning it is not the primary active compound but is metabolised in the body to produce its active form. The key metabolic conversion is catalysed by carboxylesterase enzymes, predominantly in the liver, which cleave irinotecan to release SN-38. SN-38 is the principal cytotoxic metabolite and is approximately 100 to 1,000 times more potent than irinotecan itself in inhibiting topoisomerase I. Once formed, SN-38 binds to the topoisomerase I-DNA complex and stabilises the normally transient single-strand DNA breaks that topoisomerase I creates during the process of DNA unwinding. When the DNA replication fork collides with these stabilised cleavable complexes, irreversible double-strand DNA breaks are generated. These lethal lesions trigger cell cycle arrest, primarily at the S-phase, and ultimately lead to apoptotic cell death. Because cancer cells generally have higher rates of DNA replication than most normal cells, they are disproportionately vulnerable to topoisomerase I inhibition.

The metabolism and clearance of SN-38 are clinically important because they determine both the efficacy and toxicity of irinotecan therapy. SN-38 is inactivated by the enzyme uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1), which conjugates SN-38 with glucuronic acid to form SN-38 glucuronide (SN-38G), an inactive metabolite that is excreted in bile. Patients who have genetic polymorphisms that reduce UGT1A1 activity—most notably those who are homozygous for the UGT1A1*28 allele—have impaired ability to inactivate SN-38. This leads to higher systemic exposure to the active drug and significantly increases the risk of severe diarrhoea and neutropenia. The UGT1A1*28 variant is present in approximately 10% of the Caucasian population in homozygous form, and UGT1A1 genotyping before initiation of irinotecan therapy has become an increasingly common practice in many oncology centres.

Irinotecan Actavis is indicated for the treatment of patients with advanced colorectal cancer in the following clinical settings:

• First-line combination therapy: In combination with 5-fluorouracil (5-FU) and folinic acid (leucovorin) in patients who have not received prior chemotherapy for advanced disease. This combination is the foundation of the widely used FOLFIRI regimen, which is one of the standard first-line treatment options for metastatic colorectal cancer recommended by ESMO, NCCN, and other international guideline bodies. FOLFIRI may be combined with biological agents such as bevacizumab (an anti-VEGF antibody) or cetuximab/panitumumab (anti-EGFR antibodies, in KRAS/NRAS/BRAF wild-type tumours) to further improve outcomes.
• Second-line monotherapy: As a single agent in patients whose disease has progressed on or after a prior chemotherapy regimen containing 5-fluorouracil. The monotherapy dose schedule (typically 350 mg/m² every 3 weeks) offers a treatment option for patients who are not candidates for further combination chemotherapy.

Colorectal cancer is the third most commonly diagnosed cancer worldwide and the second leading cause of cancer death, with approximately 1.9 million new cases and 935,000 deaths annually according to the World Health Organization. Approximately 20–25% of patients present with metastatic disease at diagnosis, and around 50% of patients with localised disease will eventually develop metastases. The introduction of irinotecan-based regimens in the late 1990s and early 2000s, along with oxaliplatin-based combinations (FOLFOX), transformed the treatment landscape for metastatic colorectal cancer by significantly improving response rates, progression-free survival, and overall survival compared with 5-FU/leucovorin alone.

What Should You Know Before Taking Irinotecan Actavis?

Contraindications

There are several absolute contraindications to the use of Irinotecan Actavis. Treatment must not be initiated if any of the following conditions are present:

• Hypersensitivity: Known allergy to irinotecan hydrochloride or any of the excipients in the formulation.
• Chronic inflammatory bowel disease: Patients with Crohn’s disease or ulcerative colitis must not receive irinotecan due to the high risk of severe, potentially life-threatening diarrhoea and gastrointestinal complications.
• Bowel obstruction: Irinotecan is contraindicated in patients with existing intestinal obstruction, as the drug’s gastrointestinal toxicity could critically worsen the condition.
• Severe hepatic impairment: Patients with bilirubin levels exceeding 3 times the upper limit of normal (ULN) must not receive irinotecan, as impaired hepatic metabolism leads to dangerously elevated levels of the active metabolite SN-38.
• Severe bone marrow failure: Patients with pre-existing WHO performance status greater than 2 or significant baseline myelosuppression are not candidates for irinotecan therapy.
• Pregnancy and breastfeeding: Irinotecan has demonstrated teratogenic and embryotoxic effects in animal studies and must not be used during pregnancy or while breastfeeding.
• Concomitant use with St John’s Wort: Hypericum perforatum (St John’s Wort) is a potent inducer of CYP3A4 and UGT1A1 and significantly reduces SN-38 exposure, undermining treatment efficacy. It must not be used concurrently with irinotecan.

Warnings and Precautions

Before and during treatment with irinotecan, your oncologist will carefully evaluate and monitor several important clinical parameters:

• Haematological monitoring: Complete blood counts must be obtained before each cycle of treatment. Irinotecan can cause severe neutropenia, thrombocytopenia, and anaemia. Treatment should be delayed if the neutrophil count is below 1,500/mm³ or the platelet count is below 100,000/mm³. Febrile neutropenia (fever with low neutrophils) is a medical emergency requiring hospitalisation and broad-spectrum antibiotic therapy.
• Hepatic function: Liver function tests (bilirubin, transaminases, alkaline phosphatase) should be monitored before each cycle. Dose reductions or treatment delays are necessary in patients with elevated bilirubin (1.5–3 times ULN). Patients with hepatic metastases or a history of hepatitis require particularly careful monitoring.
• UGT1A1 polymorphism: Patients who are homozygous for UGT1A1*28 (approximately 10% of Caucasians) have reduced ability to glucuronidate SN-38 and are at substantially increased risk of severe haematological and gastrointestinal toxicity. A reduced starting dose is recommended for these patients, with subsequent dose escalation guided by tolerability.
• Early cholinergic syndrome: An acute cholinergic syndrome can occur during or within the first 24 hours after infusion, characterised by early diarrhoea, abdominal cramping, rhinitis, lacrimation, miosis, salivation, and diaphoresis. This is caused by inhibition of acetylcholinesterase by irinotecan. Atropine (0.25 mg subcutaneously) is used for prophylaxis and treatment, except in patients with asthma.
• Pulmonary toxicity: Interstitial lung disease presenting as pulmonary infiltrates has been reported uncommonly with irinotecan. Risk factors include pre-existing lung disease, use of pneumotoxic drugs, radiotherapy, and colony-stimulating factors. New or worsening respiratory symptoms should be promptly investigated.
• Renal function: Although irinotecan is not primarily renally excreted, dehydration secondary to severe diarrhoea or vomiting can precipitate renal impairment. Adequate hydration must be maintained. Rare cases of renal insufficiency, hypotension, or circulatory failure have been reported in patients who experienced dehydration associated with diarrhoea and/or vomiting.
• Cardiac events: Myocardial ischaemia events have been reported uncommonly following irinotecan therapy. Patients with pre-existing cardiovascular risk factors or those who develop cardiac symptoms during treatment require close monitoring.
• Immunosuppression: As with all cytotoxic agents, irinotecan suppresses the immune system. Patients should avoid exposure to infections and should not receive live vaccines during treatment.
• Extravasation: Although irinotecan is not classified as a vesicant, extravasation can cause local tissue irritation. The infusion site should be monitored throughout administration.

Pregnancy and Breastfeeding

Irinotecan is contraindicated during pregnancy. Preclinical studies in animals have shown teratogenic effects (malformations) and embryotoxicity (embryo death) at doses below therapeutic human exposures. There are no adequate data from the use of irinotecan in pregnant women, but based on its mechanism of action and animal data, the drug is expected to cause serious harm to the developing fetus.

Women of childbearing potential must use effective contraception during treatment and for at least one month following the last dose. Men receiving irinotecan should use effective contraception during treatment and for at least three months after the last dose. Male patients should be counselled about the potential for irinotecan to impair fertility and may wish to consider sperm cryopreservation before initiating therapy.

Breastfeeding must be discontinued during irinotecan treatment. It is not known whether irinotecan or its metabolites are excreted in human breast milk, but given the serious potential for adverse effects in nursing infants, breastfeeding is not permitted during and for one month after the last dose.

How Does Irinotecan Actavis Interact with Other Drugs?

Irinotecan undergoes extensive hepatic metabolism involving multiple enzyme systems, making it susceptible to a wide range of pharmacokinetic drug interactions. The parent compound is metabolised by CYP3A4 to several inactive oxidative metabolites, while the active metabolite SN-38 is inactivated by UGT1A1-mediated glucuronidation. Drugs that affect either of these pathways can significantly alter irinotecan’s efficacy and toxicity profile.

Major Interactions

Minor Interactions

Several additional interactions should be considered, although they may be managed with appropriate monitoring rather than avoidance:

• Bevacizumab: When used in combination with irinotecan-based regimens (a common clinical practice), bevacizumab has been associated with increased incidence of severe diarrhoea and neutropenia. Close monitoring is required, but the combination is well-established as a standard treatment option. Bevacizumab may also increase the concentration of SN-38 by approximately 33%.
• 5-Fluorouracil (5-FU): The combination of irinotecan with 5-FU and folinic acid (FOLFIRI) is a standard regimen for colorectal cancer. While the combination has overlapping gastrointestinal and haematological toxicities, the regimen is well-characterised with established dose-adjustment protocols. The sequential administration (irinotecan followed by 5-FU) is preferred to minimise additive toxicity.
• Dexamethasone: Commonly used as an antiemetic premedication with irinotecan. While dexamethasone is a CYP3A4 inducer, the short-term use as antiemetic premedication is not considered clinically significant. However, chronic high-dose dexamethasone use could theoretically reduce irinotecan efficacy.
• Live vaccines: As with all immunosuppressive chemotherapy, live vaccines must be avoided during treatment with irinotecan due to the risk of severe or fatal vaccine-strain infections. Inactivated vaccines may be administered, although their immunogenicity may be reduced.
• Laxatives: The concurrent use of laxatives may exacerbate irinotecan-induced diarrhoea and should be avoided, particularly in the period surrounding drug administration.

Patients should inform their oncologist about all medications they are taking, including over-the-counter drugs, herbal supplements, and vitamins, before starting irinotecan therapy. This allows for comprehensive interaction screening and appropriate management.

What Is the Correct Dosage of Irinotecan Actavis?

Irinotecan Actavis must only be administered under the supervision of a physician experienced in the use of anticancer chemotherapy, in a setting with adequate facilities for managing the serious complications that may occur. The dosage is individualised based on the patient’s body surface area, overall clinical condition, hepatic function, and haematological parameters. All patients must have adequate neutrophil counts (at least 1,500/mm³), platelet counts (at least 100,000/mm³), and bilirubin levels (no more than 1.5 times ULN for combination therapy, or 3 times ULN for monotherapy) before each treatment cycle.

Adults

In the FOLFIRI regimen, irinotecan is typically administered on day 1 as a 90-minute intravenous infusion, followed by leucovorin (folinic acid) and then 5-fluorouracil (bolus and 46-hour continuous infusion). The cycle is repeated every 14 days. When combined with bevacizumab, the anti-VEGF antibody is administered before the irinotecan infusion. The total number of cycles is determined by tumour response, disease progression, and patient tolerability, with treatment continuing for as long as benefit is maintained.

For monotherapy, the recommended starting dose of 350 mg/m² is given every 3 weeks. This regimen is typically used as second-line treatment in patients who have failed 5-FU-based chemotherapy. Dose modifications are based on the worst toxicity experienced in the preceding cycle.

Children

Irinotecan Actavis is not recommended for use in children. The safety and efficacy of irinotecan in paediatric patients have not been established for the approved colorectal cancer indication. While irinotecan is sometimes used in paediatric oncology for certain brain tumours and other solid tumours, these represent off-label use and should only be considered within the context of clinical trials or established paediatric oncology protocols.

Elderly

No specific dose adjustment is required for elderly patients solely based on age. However, elderly patients may have reduced physiological reserve and are more likely to have comorbidities that can increase the risk of irinotecan toxicity. Close monitoring is recommended, particularly during the first treatment cycle, as elderly patients are more susceptible to diarrhoea and its consequences (dehydration, electrolyte imbalances, renal impairment). The starting dose should be carefully considered in the context of the patient’s overall functional status and comorbidities.

Missed Dose

As irinotecan is administered in a hospital or clinic setting by healthcare professionals, missed doses in the traditional sense do not typically occur. However, treatment cycles may be delayed for various reasons including insufficient haematological recovery, unresolved toxicity from previous cycles, or intercurrent illness. If a cycle is delayed, treatment should resume at the previously tolerated dose once the patient meets the re-treatment criteria (adequate neutrophil count, platelet count, and bilirubin levels, and resolution of non-haematological toxicities to Grade 1 or less).

Overdose

There is no specific antidote for irinotecan overdose. In the event of overdose, the expected toxicities are severe exaggerations of the known dose-limiting side effects: life-threatening neutropenia and severe diarrhoea. Treatment is supportive and should include aggressive hydration, electrolyte replacement, anti-infective therapy for neutropenic complications, and intensive monitoring in a hospital setting. Colony-stimulating factors (G-CSF) should be administered to mitigate neutropenia. Haemodialysis is not expected to be effective given the high protein binding of both irinotecan and SN-38.

What Are the Side Effects of Irinotecan Actavis?

Like all cytotoxic chemotherapy agents, irinotecan causes a range of side effects. The following frequency categories are based on post-marketing surveillance data and clinical trial results. Not every patient will experience all of these effects, and their severity can vary considerably between individuals. Your oncology team will monitor you closely and manage side effects proactively.

The management of irinotecan side effects requires a proactive, multidisciplinary approach. Patients must be thoroughly educated about the recognition and early management of late-onset diarrhoea before starting treatment. Antiemetic prophylaxis (typically with a 5-HT3 receptor antagonist such as ondansetron, with or without dexamethasone) should be administered before each infusion. Atropine should be available for the treatment of acute cholinergic syndrome. Regular blood count monitoring is essential for early detection and management of haematological toxicity.

How Should You Store Irinotecan Actavis?

Irinotecan Actavis is supplied as a clear, pale yellow concentrate for solution for infusion in glass vials. Proper storage is essential to maintain the chemical and physical stability of the product:

• Unopened vials: Store below 25°C. Keep in the original carton to protect from light. Do not freeze. The shelf life of the unopened product is as stated on the packaging.
• Diluted solution: After dilution in 5% glucose solution or 0.9% sodium chloride solution, the infusion should ideally be used immediately. Chemical and physical in-use stability has been demonstrated for up to 24 hours when refrigerated at 2–8°C and up to 48 hours when stored at or below 25°C. From a microbiological standpoint, the product should be used immediately after preparation. If not used immediately, in-use storage times and conditions are the responsibility of the user.
• Do not use after the expiry date printed on the vial and outer packaging.
• Inspect visually before use. The solution should be clear and pale yellow. Do not use if the solution is discoloured, cloudy, or contains visible particles.
• Cytotoxic handling: As a cytotoxic agent, irinotecan must be prepared and handled according to local guidelines for hazardous drugs. This includes the use of protective clothing, gloves, and preparation in a biological safety cabinet. Any unused product or waste material should be disposed of in accordance with local requirements for cytotoxic waste.

Keep this medicine out of the sight and reach of children. As irinotecan is administered in a healthcare setting, storage and handling are the responsibility of the hospital pharmacy and oncology nursing team.

What Does Irinotecan Actavis Contain?

The complete qualitative composition of Irinotecan Actavis concentrate for solution for infusion is as follows:

Active Substance

Each millilitre contains 20 mg of irinotecan hydrochloride trihydrate. This is equivalent to approximately 17.33 mg of irinotecan free base per millilitre. The product is available in vials of different sizes (typically 2 ml, 5 ml, 15 ml, and 25 ml), allowing flexible dosing based on the patient’s calculated body surface area. Irinotecan hydrochloride trihydrate has the molecular formula C₃₃H₃₈N₄O₆·HCl·3H₂O and a molecular weight of 677.19 g/mol.

Excipients (Inactive Ingredients)

• Sorbitol (E420): Used as a stabiliser and osmolality-adjusting agent. Patients with rare hereditary fructose intolerance should be aware of the sorbitol content.
• Lactic acid: Used as a pH-adjusting agent to maintain solution stability.
• Sodium hydroxide: Used for pH adjustment.
• Hydrochloric acid: Used for pH adjustment.
• Water for injections: The solvent for the concentrate.

The concentrate is a clear, pale yellow solution with a pH of approximately 3.5. Before administration, it must be diluted to an appropriate volume using either 5% glucose (dextrose) solution or 0.9% sodium chloride solution to achieve a final concentration in the range of 0.12 to 2.8 mg/ml. The diluted solution should be mixed thoroughly by gentle inversion. It must never be mixed with other medicinal products in the same infusion bag.