Irinotecan

Trade Names:
Camptosar
- Injection 20 mg/mL, containing sorbitol 45 mg

Pharmacology

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Irinotecan is a derivative of camptothecin. Camptothecins interact specifically with the enzyme topoisomerase I, which relieves torsional strain in DNA by inducing reversible single-strand breaks.

Pharmacokinetics

Absorption

T _max is 1 h (active metabolite).

Distribution

30 to 68% protein bound; approximately 95% of active metabolites protein bound.

Metabolism

SN-38 is the active metabolite. Metabolism occurs in the liver.

Elimination

The t _½ is approximately 6 h. Approximately 10 h for the active metabolite. Primarily excreted in the urine.

Indications and Usage

Metastatic cancer of the colon or rectum after standard treatment with fluorouracil.

Unlabeled Uses

Cervical cancer, lung cancer (small cell or non-small cell), ovarian cancer.

Contraindications

Standard considerations.

Dosage and Administration

IV Cycle 1 : Irinotecan 125 mg/m ² once weekly for 4 wk followed by 2 wk of rest. Subsequent cycles : Give irinotecan once weekly for 4 wk, followed by 2 wk of rest. Based on response and adverse reactions, the dose may be adjusted in 25 to 50 mg/m ² increments. The weekly dose may be increased to a max of 150 mg/m ² or decreased to a min of 50 mg/m ² . Alternate schedule : Irinotecan 350 mg/m ² IV once every 21 days. Give an initial dose of irinotecan 300 mg/m ² IV every 21 days in patients 70 yr of age and older, patients with prior pelvic or abdominal radiation, or patients with a performance status of 2. Based on adverse reactions, the dose may be decreased in 50 mg/m ² increments to a min of 200 mg/m ² (max, 350 mg/m ² ).

IV Once-daily regimen : Dosage should be 125 mg/m ² if serum bilirubin is less than 1 mg/dL. If bilirubin concentration is 1 to 2 mg/dL, dosage should be 100 mg/m ³ . Irinotecan is not recommended if bilirubin is more than 2 mg/dL. Every 21-day regimen : Dosage should be 350 mg/m ² if serum bilirubin is less than 1 mg/dL. If bilirubin concentration is 1 to 2 mg/dL, dosage should be 300 mg/m ² . Irinotecan is not recommended if bilirubin is more than 2 mg/dL.

Storage/Stability

Store solution for injection at room temperature and protect from light. Store in the protective packaging until just before use.

Drug Interactions

Irinotecan adverse reactions (eg, myelosuppression, diarrhea) would possibly be exacerbated by other antineoplastics having similar adverse reactions.

It is possible that coadministration of dexamethasone and irinotecan may enhance the likelihood of lymphocytopenia. Dexamethasone given as emetic prophylaxis can contribute to hyperglycemia in some patients.

Laxative therapy during irinotecan therapy may increase the severity of diarrhea, but this has not been studied.

The incidence of akathisia in clinical trials was greater (8.5%) when prochlorperazine was administered on the same day as irinotecan than when these drugs were given on separate days (1.3%).

The health care provider may wish to withhold diuretics during irinotecan dosing during periods of active vomiting or diarrhea because of the potential risk of dehydration secondary to irinotecan-induced vomiting and diarrhea.

Laboratory Test Interactions

None well documented.

Adverse Reactions

Cardiovascular

Flushing; edema.

CNS

Insomnia; headache; dizziness.

Dermatologic

Alopecia; sweating; rash.

GI

Diarrhea (“early” occurring within 24 h after infusion or “late” occurring an average of 11 to 18 days after infusion); moderate to high potential for nausea and vomiting; anorexia; constipation; flatulence; stomatitis; dyspepsia; abdominal pain; increased LFTs.

Hematologic

Leukopenia; lymphocytopenia; anemia; moderate to severe neutropenia. Neutrophil nadir occurs between days 15 to 27 with once weekly dosing and at days 8 to 9 with 21-day cycles.

Respiratory

Dyspnea; cough; rhinitis.

Miscellaneous

Fever; pain; chills.

Precautions

Pregnancy

Category D .

Lactation

Discontinue breast-feeding when receiving therapy with irinotecan.

Children

Safety and efficacy not established.

Elderly

Exercise particular caution in monitoring the effects of irinotecan in the elderly (ie, 65 yr of age and older).

Hypersensitivity

Hypersensitivity reactions including severe anaphylactic or anaphylactoid reactions have been observed.

Renal Function

Rare cases of renal function impairment and acute renal failure have been identified, usually in patients who became volume-depleted from severe vomiting or diarrhea.

Special Risk Patients

It has been noted that patients with modestly elevated baseline serum total bilirubin levels (1 to 2 mg/dL) have had a significantly greater likelihood of experiencing first-course grade 3 or 4 neutropenia than those with bilirubin levels that were less than 1 mg/dL.

Toxic deaths

Do not use in combination with the “Mayo Clinic” regimen of 5-FU/LV because of reports of increased toxicity, including toxic deaths. Use irinotecan as recommended.

Irradiation

Patients who have previously received pelvic/abdominal irradiation are at an increased risk of severe myelosuppression following irinotecan administration.

Extravasation

Local irritation or phlebitis may occur. Refer to the institution-specific protocol.

Adverse reactions requiring irinotecan dosage modification

See manufacturer's recommendations.

Patient Information

• Instruct patients to call the health care provider if experiencing more than 3 days of diarrhea.
• Inform patients and caregivers of the expected toxic effects of irinotecan, particularly of its GI manifestations, such as nausea, vomiting, and diarrhea. Instruct each patient to have loperamide readily available and to begin treatment for late diarrhea (generally occurring more than 24 h after administration) at the first episode of poorly formed or loose stools or the earliest onset of bowel movements more frequent than normally expected for the patient. One dosage regimen for loperamide is 4 mg at the first onset of late diarrhea and then 2 mg every 2 h until the patient is diarrhea-free for at least 12 h. During the night, the patient may take 4 mg loperamide every 4 h. Notify health care provider if diarrhea occurs. Premedication with loperamide is not recommended.
• Avoid the use of drugs with laxative properties because of the potential for exacerbation of diarrhea. Advise patients to contact the health care provider to discuss any laxative use.
• Consult health care provider if vomiting or fever occurs or evidence of infection develops, of if symptoms of dehydration, such as fainting, lightheadedness, or dizziness are noted following irinotecan therapy.

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