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Pronunciation:

(floo SYE toe seen)

U.S. Brand Names:

Ancobon®

Synonyms:

5-FC; 5-Flurocytosine

Generic Available:

Canadian Brand Names:

Ancobon®

Use:

Adjunctive treatment of susceptible fungal infections (usually Candida or Cryptococcus); synergy with amphotericin B for certain fungal infections (Cryptococcus spp., Candida spp.)

Pregnancy Risk Factor:

Pregnancy Implications:

Teratogenic in some animal studies, however, there are no adequate and well-controlled studies in pregnant women.

Lactation:

Excretion in breast milk unknown/not recommended

Contraindications:

Hypersensitivity to flucytosine or any component of the formulation

Warnings/Precautions:

Use with extreme caution in patients with renal dysfunction; dosage adjustment required. Avoid use as monotherapy; resistance rapidly develops. Use with caution in patients with bone marrow depression; patients with hematologic disease or who have been treated with radiation or drugs that suppress the bone marrow may be at greatest risk. Bone marrow toxicity can be irreversible.

Adverse Reactions:

Frequency not defined.

Cardiovascular: Cardiac arrest, myocardial toxicity, ventricular dysfunction, chest pain

Central nervous system: Confusion, headache, hallucinations, dizziness, drowsiness, psychosis, parkinsonism, ataxia, sedation, pyrexia, seizure, fatigue

Dermatologic: Rash, photosensitivity, pruritus, urticaria, Lyell's syndrome

Endocrine & metabolic: Temporary growth failure, hypoglycemia, hypokalemia

Gastrointestinal: Nausea, vomiting, diarrhea, abdominal pain, loss of appetite, dry mouth, hemorrhage, ulcerative colitis

Hematologic: Bone marrow suppression, anemia, leukopenia, thrombocytopenia, agranulocytosis, aplastic anemia, eosinophilia, pancytopenia

Hepatic: Liver enzymes increased, hepatitis, jaundice, azotemia, bilirubin increased

Neuromuscular & skeletal: Peripheral neuropathy, paresthesia, weakness

Otic: Hearing loss

Renal: BUN and serum creatinine increased, renal failure, azotemia, crystalluria

Respiratory: Respiratory arrest, dyspnea

Miscellaneous: Anaphylaxis, allergic reaction

Overdosage/Toxicology:

Symptoms of overdose include nausea, vomiting, diarrhea, hepatitis, and bone marrow suppression. Treatment is supportive. Removed by hemodialysis.

Drug Interactions:

Increased effect/toxicity with concurrent amphotericin administration; cytarabine may inactivate flucytosine activity

Ethanol/Nutrition/Herb Interactions:

Food: Food decreases the rate, but not the extent of absorption.

Stability:

Store at 25°C (77°F); protect from light

Mechanism of Action:

Penetrates fungal cells and is converted to fluorouracil which competes with uracil interfering with fungal RNA and protein synthesis

Pharmacodynamics/Kinetics:

Absorption: 75% to 90%

Distribution: Into CSF, aqueous humor, joints, peritoneal fluid, and bronchial secretions; Vd: 0.6 L/kg

Protein binding: 2% to 4%

Metabolism: Minimally hepatic; deaminated, possibly via gut bacteria, to 5-fluorouracil

Half-life elimination:

Normal renal function: 2-5 hours

Anuria: 85 hours (range: 30-250)

End stage renal disease: 75-200 hours

Time to peak, serum: ~2-6 hours

Excretion: Urine (>90% as unchanged drug)

Dosage:

Children and Adults: Oral: 50-150 mg/kg/day in divided doses every 6 hours

Dosing interval in renal impairment: Use lower initial dose:

Clcr 20-40 mL/minute: Administer every 12 hours

Clcr 10-20 mL/minute: Administer every 24 hours

Clcr<10 mL/minute: Administer every 24-48 hours

Hemodialysis: Dialyzable (50% to 100%); administer dose posthemodialysis

Peritoneal dialysis: Adults: Administer 0.5-1 g every 24 hours

Continuous arteriovenous or venovenous hemodiafiltration effects: Dose as for Clcr 10-50 mL/minute

Administration:

Administer around-the-clock to promote less variation in peak and trough serum levels. To avoid nausea and vomiting, administer a few capsules at a time over 15 minutes until full dose is taken.

Monitoring Parameters:

Pretreatment: Electrolytes, CBC, BUN, renal function, blood culture

During treatment: CBC and LFTS frequently, serum flucytosine concentration, renal function

Reference Range:

Therapeutic: 25-100 mcg/mL (peak) (SI: 195-775 mol/L); peak levels should not exceed 100-120 mcg/mL to avoid toxic bone marrow depressive effects

Trough: Draw just prior to dose administration

Peak: Draw 2 hours after an oral dose administration

Test Interactions:

Flucytosine causes markedly false elevations in serum creatinine values when the Ektachem® analyzer is used

Patient Education:

Inform prescriber of all prescriptions, OTC medications, or herbal products you are taking, and any allergies you have. Do not take any new medication during therapy unless approved by prescriber. Take capsules one at a time over a few minutes with food to reduce GI upset. Take full course of medication as ordered. Do not discontinue without consulting prescriber. Practice good hygiene measures to prevent reinfection. Frequent blood tests may be required. May cause nausea and vomiting (small, frequent meals may help). Report rash; respiratory difficulty; CNS changes (eg, confusion, hallucinations, ataxia, acute headache); yellowing of skin or eyes; changes in color of stool or urine; unresolved diarrhea or anorexia; or unusual bleeding, fatigue, or weakness. Pregnancy/breast-feeding precautions: Inform prescriber if you are or intend to become pregnant. Breast-feeding is not recommended.

Dental Health: Effects on Dental Treatment:

No significant effects or complications reported

Dental Health: Vasoconstrictor/Local Anesthetic Precautions:

No information available to require special precautions

Mental Health: Effects on Mental Status:

May rarely cause drowsiness, confusion, or hallucinations

Mental Health: Effects on Psychiatric Treatment:

May cause bone marrow suppression; use caution with clozapine and carbamazepine

Oncology: Emetic Potential:

Very low (<10%)

Dosage Forms:

Capsule: 250 mg, 500 mg

Extemporaneously Prepared:

Flucytosine oral liquid has been prepared by using the contents of ten 500 mg capsules triturated in a mortar and pestle with a small amount of distilled water; the mixture was transferred to a 500 mL volumetric flask; the mortar was rinsed several times with a small amount of distilled water and the fluid added to the flask; sufficient distilled water was added to make a total volume of 500 mL of a 10 mg/mL liquid; oral liquid was stable for 70 days when stored in glass or plastic prescription bottles at 4°C or for up to 14 days at room temperature.

Wintermeyer SM and Nahata MC, "Stability of Flucytosine in an Extemporaneously Compounded Oral Liquid,"Am J Health Syst Pharm, 1996, 53:407-9.

International Brand Names:

Alcobon® (GB, NZ); Ancobon® (CA); Ancotil® (AT, AU, BR, CH, CZ, DE, DK, FR, GB, HK, IE, IT, NL, PL, SE); Cocol® (JP)

References

Baley JE, Meyers C, Kliegman RM, et al, "Pharmacokinetics, Outcome of Treatment, and Toxic Effects of Amphotericin B and 5-Fluorocytosine in Neonates,"J Pediatr, 1990, 116(5):791-7.

Lau AH and Kronfol NO, "Elimination of Flucytosine by Continuous Hemofiltration,"Am J Nephrol, 1995, 15(4):327-31.

Lyman CA and Walsh TJ, "Systemically Administered Antifungal Agents. A Review of Their Clinical Pharmacology and Therapeutic Applications,"Drugs, 1992, 44(1):9-35.

Patel R, "Antifungal Agents. Part I. Amphotericin B Preparations and Flucytosine,"Mayo Clin Proc, 1998, 73(12):1205-25.

Saag MS, Graybill RJ, Larsen RA, et al, "Practice Guidelines for the Management of Cryptococcal Disease. Infectious Diseases Society of America,"Clin Infect Dis, 2000, 30(4):710-8.

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