Ancobon (flucytosine), an antifungal agent, is available as 250mg and 500mg capsules for oral administration. Each capsule also contains corn starch, lactose and talc. Gelatin capsule shells contain parabens (butyl, methyl, propyl) and sodium propionate, with the following dye systems: 250-mg capsules — black iron oxide, FD&C Blue No. 1, FD&C Yellow No. 6, D&C Yellow No. 10 and titanium dioxide; 500mg capsules — black iron oxide and titanium dioxide. Chemically, flucytosine is 5-fluorocytosine, a fluorinated pyrimidine which is related to fluorouracil and floxuridine. It is a white to off-white crystalline powder with a molecular weight of 129.09 and the following structural formula:

Ancobon is indicated only in the treatment of serious infections caused by susceptible strains of Candida and/or Cryptococcus.

Candida: Septicemia, endocarditis and urinary system infections have been effectively treated with flucytosine. Limited trials in pulmonary infections justify the use of flucytosine.

Cryptococcus: Meningitis and pulmonary infections have been treated effectively. Studies in septicemias and urinary tract infections are limited, but good responses have been reported.

Ancobon should be used in combination with amphotericin B for the treatment of systemic candidiasis and cryptococcosis because of the emergence of resistance to Ancobon (See Microbiology).

The usual dosage of Ancobon is 50 to 150 mg/kg/day administered in divided doses at 6-hour intervals. Nausea or vomiting may be reduced or avoided if the capsules are given a few at a time over a 15-minute period. If the BUN or the serum creatinine is elevated, or if there are other signs of renal impairment, the initial dose should be at the lower level (see WARNINGS).

Ancobon should be used in combination with amphotericin B for the treatment of systemic candidiasis and cryptococcosis because of the emergence of resistance to Ancobon (See Microbiology).

Capsules, 250 mg (gray and green), imprinted ANCOBON® 250 ICN, bottles of 100 (NDC 0187-3554-10). Capsules, 500 mg (gray and white), imprinted ANCOBON® 500 ICN, bottles of 100 (NDC 0187-3555-10). Store at 25°C (77°F); excursions permitted to 15°C - 30°C (59°F - 86°F).

Valeant Pharmaceuticals International, 3300 Hyland Avenue, Costa Mesa, California 92626. 714-545-0100. Rev. May 2006. FDA Rev date: 8/10/2006

The adverse reactions which have occurred during treatment with Ancobon are grouped according to organ system affected.

Cardiovascular: Cardiac arrest, myocardial toxicity, ventricular dysfunction.

Respiratory: Respiratory arrest, chest pain, dyspnea.

Dermatologic: Rash, pruritus, urticaria, photosensitivity.

Gastrointestinal: Nausea, emesis, abdominal pain, diarrhea, anorexia, dry mouth, duodenal ulcer, gastrointestinal hemorrhage, acute hepatic injury with possible fatal outcome in debilitated patients, hepatic dysfunction, jaundice, ulcerative colitis, bilirubin elevation, increased hepatic enzymes.

Genitourinary: Azotemia, creatinine and BUN elevation, crystalluria, renal failure.

Hematologic: Anemia, agranulocytosis, aplastic anemia, eosinophilia, leukopenia, pancytopenia, thrombocytopenia

Neurologic: Ataxia, hearing loss, headache, paresthesia, parkinsonism, peripheral neuropathy, pyrexia, vertigo, sedation, convulsions. Psychiatric: Confusion, hallucinations, psychosis.

Miscellaneous: Fatigue, hypoglycemia, hypokalemia, weakness, allergic reactions, Lyell's syndrome.

Cytosine arabinoside, a cytostatic agent, has been reported to inactivate the antifungal activity of Ancobon by competitive inhibition. Drugs which impair glomerular filtration may prolong the biological half-life of flucytosine.

Drug/Laboratory Test Interactions

Measurement of serum creatinine levels should be determined by the Jaffé reaction, since Ancobon does not interfere with the determination of creatinine values by this method. Most automated equipment for measurement of creatinine makes use of the Jaffé reaction.

Ancobon must be given with extreme caution to patients with impaired renal function. Since Ancobon is excreted primarily by the kidneys, renal impairment may lead to accumulation of the drug. Ancobon serum concentrations should be monitored to determine the adequacy of renal excretion in such patients. Dosage adjustments should be made in patients with renal insufficiency to prevent progressive accumulation of active drug.

Ancobon must be given with extreme caution to patients with bone marrow depression. Patients may be more prone to depression of bone marrow function if they: 1) have a hematologic disease, 2) are being treated with radiation or drugs which depress bone marrow, or 3) have a history of treatment with such drugs or radiation. Bone marrow toxicity can be irreversible and may lead to death in immunosuppressed patients. Frequent monitoring of hepatic function and of the hematopoietic system is indicated during therapy.

General

Before therapy with Ancobon is instituted, electrolytes (because of hypokalemia) and the hematologic and renal status of the patient should be determined (see WARNINGS). Close monitoring of the patient during therapy is essential.

Laboratory Tests

Since renal impairment can cause progressive accumulation of the drug, blood concentrations and kidney function should be monitored during therapy. Hematologic status (leucocyte and thrombocyte count) and liver function (alkaline phosphatase, SGOT and SGPT) should be determined at frequent intervals during treatment as indicated.

Carcinogenesis, Mutagenesis, Impairment of Fertility

Flucytosine has not undergone adequate animal testing to evaluate carcinogenic potential. The mutagenic potential of flucytosine was evaluated in Ames-type studies with five different mutants of S. typhimurium and no mutagenicity was detected in the presence or absence of activating enzymes. Flucytosine was nonmutagenic in three different repair assay systems (i.e., rec, uvr and pol).

There have been no adequate trials in animals on the effects of flucytosine on fertility or reproductive performance. The fertility and reproductive performance of the offspring (F₁ generation) of mice treated with 100 mg/kg/day (345 mg/M²/day or 0.059 times the human dose), 200 mg/kg/day (690 mg/M²/day or 0.118 times the human dose) or 400 mg/kg/day (1380 mg/M²/day or 0.236 times the human dose) of flucytosine on days 7 to 13 of gestation was studied; the in utero treatment had no adverse effect on the fertility or reproductive performance of the offspring.

Pregnancy

Teratogenic Effects. Pregnancy Category C

Flucytosine was shown to be teratogenic (vertebral fusions) in the rat at doses of 40 mg/kg/day (298 mg/M²/day or 0.051 times the human dose) administered on days 7 to 13 of gestation. At higher doses (700 mg/kg/day; 5208 mg/M²/day or 0.89 times the human dose administered on days 9 to 12 of gestation), cleft lip and palate and micrognathia were reported. Flucytosine was not teratogenic in rabbits up to a dose of 100 mg/kg/day (1423 mg/M²/day or 0.243 times the human dose) administered on days 6 to 18 of gestation. In mice, 400 mg/kg/day of flucytosine (1380 mg/M²/day or 0.236 times the human dose) administered on days 7 to 13 of gestation was associated with a low incidence of cleft palate that was not statistically significant. There are no adequate and well-controlled studies in pregnant women. Ancobon should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Nursing Mothers

It is not known whether this drug is excreted in human milk. Because many drugs are excreted in human milk and because of the potential for serious adverse reactions in nursing infants from Ancobon, a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother.

Pediatric Use

The efficacy and safety of Ancobon have not been systematically studied in pediatric patients. A small number of neonates have been treated with 25 to 200 mg/kg/day of flucytosine, with and without the addition of amphotericin B, for systemic candidiasis. No unexpected adverse reactions were reported in these patients. It should be noted, however, that hypokalemia and acidemia were reported in one patient who received flucytosine in combination with amphotericin B, and anemia was observed in a second patient who received flucytosine alone. Transient thrombocytopenia was noted in two additional patients, one of whom also received amphotericin B.

There is no experience with intentional overdosage. It is reasonable to expect that overdosage may produce pronounced manifestations of the known clinical adverse reactions. Prolonged serum concentrations in excess of 100 µg/mL may be associated with an increased incidence of toxicity, especially gastrointestinal (diarrhea, nausea, vomiting), hematologic (leukopenia, thrombocytopenia) and hepatic (hepatitis).

In the management of overdosage, prompt gastric lavage or the use of an emetic is recommended. Adequate fluid intake should be maintained, by the intravenous route if necessary, since Ancobon is excreted unchanged via the renal tract. The hematologic parameters should be monitored frequently; liver and kidney function should be carefully monitored. Should any abnormalities appear in any of these parameters, appropriate therapeutic measures should be instituted.

Since hemodialysis has been shown to rapidly reduce serum concentrations in anuric patients, this method may be considered in the management of overdosage.

Ancobon should not be used in patients with a known hypersensitivity to the drug.

Flucytosine is rapidly and virtually completely absorbed following oral administration. Ancobon is not metabolized significantly when given orally to man. Bioavailability estimated by comparing the area under the curve of serum concentrations after oral and intravenous administration showed 78% to 89% absorption of the oral dose. Peak serum concentrations of 30 to 40 µg/mL were reached within 2 hours of administration of a 2g oral dose to normal subjects. Other studies revealed mean serum concentrations of approximately 70 to 80 µg/mL 1 to 2 hours after a dose in patients with normal renal function receiving a 6-week regimen of flucytosine (150 mg/kg/day given in divided doses every 6 hours) in combination with amphotericin B. The half-life in the majority of healthy subjects ranged between 2.4 and 4.8 hours. Flucytosine is excreted via the kidneys by means of glomerular filtration without significant tubular reabsorption. More than 90% of the total radioactivity after oral administration was recovered in the urine as intact drug. Flucytosine is deaminated (probably by gut bacteria) to 5-fluorouracil. The area under the curve (AUC) ratio of 5-fluorouracil to flucytosine is 4%. Approximately 1% of the dose is present in the urine as the α-fluoro-β-ureido-propionic acid metabolite. A small portion of the dose is excreted in the feces.

The half-life of flucytosine is prolonged in patients with renal insufficiency; the average half-life in nephrectomized or anuric patients was 85 hours (range: 29.9 to 250 hours). A linear correlation was found between the elimination rate constant of flucytosine and creatinine clearance.

In vitro studies have shown that 2.9% to 4% of flucytosine is protein-bound over the range of therapeutic concentrations found in the blood. Flucytosine readily penetrates the blood-brain barrier, achieving clinically significant concentrations in cerebrospinal fluid.

Pharmacokinetics in Pediatric Patients

Limited data are available regarding the pharmacokinetics of Ancobon administered to neonatal patients being treated for systemic candidiasis. After five days of continuous therapy, median peak levels in infants were 19.6 µg/mL, 27.7 µg/mL, and 83.9 µg/mL at doses of 25 mg/kg (N=3), 50 mg/kg (N=4), and 100 mg/kg (N=3), respectively. Mean time to peak serum levels was of 2.5 ± 1.3 hours, similar to that observed in adult patients. A good deal of interindividual variability was noted, which did not correlate with gestational age. Some patients had serum levels > 100 µg/mL, suggesting a need for drug level monitoring during therapy. In another study, serum concentrations were determined during flucytosine therapy in two patients (total assays performed =10). Median serum flucytosine concentrations at steady state were calculated to be 57 ± 10 µg/mL (doses of 50 to 125 mg/kg/day, normalized to 25 mg/kg per dose for comparison). In three infants receiving flucytosine 25 mg/kg/day (four divided doses), a median flucytosine half-life of 7.4 hours was observed, approximately double that seen in adult patients. The concentration of flucytosine in the cerebrospinal fluid of one infant was 43 µg/mL 3 hours after a 25 mg oral dose, and ranged from 20 to 67 mg/L in another neonate receiving oral doses of 120 to 150 mg/kg/day.

Microbiology

Mechanism of Action

Flucytosine is taken up by fungal organisms via the enzyme cytosine permease. Inside the fungal cell, flucytosine is rapidly converted to fluorouracil by the enzyme cytosine deaminase. Fluorouracil exerts its antifungal activity through the subsequent conversion into several active metabolites, which inhibit protein synthesis by being falsely incorporated into fungal RNA or interfere with the biosynthesis of fungal DNA through the inhibition of the enzyme thymidylate synthetase.

Activity In Vitro

Flucytosine exhibited activity against Candida species and Cryptococcus neoformans. In vitro activity of flucytosine is affected by the test conditions. It is essential to follow the approved standard method guidelines.¹

Susceptibility Tests

Cryptococcus neoformans:

No interpretive criteria have been established for Cryptococcus neoformans¹.

Candida

Quantitative methods are used to determine antimicrobial minimum inhibitory concentrations (MICs). These MICs provide estimates of the susceptibility of yeasts to antimicrobial compounds. The MICs should be determined using a standardized procedure. Standardized procedures are based on a dilution method¹ with standardized inoculum concentrations and standardized concentrations of flucytosine powder. The MIC values should be interpreted according to the following criteria:

A report of "Susceptible" indicates that the pathogen is likely to be inhibited if the antimicrobial compound in the blood reaches the concentration usually achievable. A report of "Intermediate" indicates that the result should be considered equivocal, and, if the microorganism is not fully susceptible to alternative, clinically feasible drugs, the test should be repeated. This category implies possible clinical applicability in body sites where the drug is physiologically concentrated or in situations where a high dosage of drug can be used. This category also provides a buffer zone which prevents small uncontrolled technical factors from causing major discrepancies in interpretation. A report of "Resistant" indicates that the pathogen is not likely to be inhibited if the antimicrobial compound in the blood reaches the concentration usually achievable; other therapy should be selected. Because of other significant host factors, in vitro susceptibility may not correlate with clinical outcomes.

Standardized susceptibility test procedures require the use of laboratory control microorganisms to control the technical aspects of the laboratory procedures. Standard flucytosine powder should provide the following MIC values:

Acceptable ranges of MICs (µg/mL) for control strains for 48-hour reference broth macrodilution testing:

Acceptable ranges of MICs (µg/mL) for control strains for 24-hour and 48-hour reference broth microdilution testing:

Drug Resistance

Flucytosine resistance may arise from a mutation of an enzyme necessary for the cellular uptake or metabolism of flucytosine or from an increased synthesis of pyrimidines, which compete with the active metabolites of flucytosine (fluorinated antimetabolites). Resistance to flucytosine has been shown to develop during monotherapy after prolonged exposure to the drug.

Drug Combination

Antifungal synergism between flucytosine and polyene antibiotics, particularly amphotericin B has been reported in vitro. Ancobon is usually administered in combination with amphotericin B due to lack of cross-resistance and reported synergistic activity of both drugs.

REFERENCES

1. Clinical and Laboratory Standards Institute. Reference Method for Broth Dilution Antifungal Susceptibility Testing of Yeasts; Approved Standard-Second Edition. NCCLS Document M27-A2, 2002 Volume 22, No 15, NCCLS, Wayne, PA, August 2002.

No information provided. Please refer to the WARNINGS and PRECAUTIONS sections.

IMPORTANT NOTE: This is a summary and does not contain all possible information about this product. For complete information about this product or your specific health needs, ask your health care professional. Always seek the advice of your health care professional if you have any questions about this product or your medical condition. This information is not intended as individual medical advice and does not substitute for the knowledge and judgment of your health care professional. This information does not contain any assurances that this product is safe, effective, or appropriate for you.

FLUCYTOSINE - ORAL

(flew-SYE-toe-seen)

COMMON BRAND NAME(S): Ancobon

WARNING: This medication should be used with increased caution if you have certain kidney problems (decreased kidney function). In this case, the body cannot get rid of flucytosine as easily with decreased kidney function, and you may develop higher-than-normal blood levels of this medication. This can cause serious (sometimes fatal) problems such as liver disease and low numbers of certain blood cells (white and red cells, platelets), which can lead to serious infections. If you have decreased kidney function, tell your doctor before starting flucytosine.

To decrease the risk of blood cell/liver problems, your doctor will order certain lab blood tests (blood cell counts, liver tests, flucytosine blood levels) and decrease your dose of flucytosine as needed.

USES: This medication is used with other medications to treat fungal infections of the blood, heart, bladder, kidneys, or brain. Flucytosine belongs to a class of drugs known as antifungals. It works by slowing the growth of certain types of fungus.

HOW TO USE: Take this medication by mouth, usually 4 times daily or exactly as directed by your doctor. If nausea/vomiting occur, take 1-2 capsules every 2-5 minutes until the full dose is taken over 15 minutes.

Dosage is based on your medical condition, kidney function, body weight, and response to therapy.

This medication works best when the amount of drug in your body is kept at a constant level. Therefore, take this drug at evenly spaced intervals. To help you remember, take it at the same times each day.

It is very important to continue taking this medication (and other antifungal medications) exactly as prescribed by your doctor. Do not take more or less of this drug than prescribed or stop taking it (or other antifungal medicines) even for a short time unless directed to do so by your doctor. Skipping or changing your dose without approval from your doctor may cause the amount of fungus to increase, make the infection more difficult to treat (resistant), or worsen side effects.

Inform your doctor immediately if your condition persists or worsens.

SIDE EFFECTS: See also Warning and How to Use sections.

Abdominal/stomach pain, diarrhea, dry mouth, headache, or drowsiness may occur. If any of these effects persist or worsen, tell your doctor or pharmacist promptly.

Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

Tell your doctor immediately if any of these unlikely but serious side effects occur: signs of a serious infection (e.g., new fever/cough, severe chills, body aches, persistent sore throat), signs of low red blood cells (e.g., increasing tiredness, pale skin, bluish lips/fingernails, shortness of breath at rest, fast heartbeat at rest), signs of serious liver problems (persistent nausea, vomiting, stomach/abdominal pain/tenderness, severe tiredness, dark urine, yellowing eyes/skin), easy bruising/bleeding, muscle weakness/cramping, decreased amount of urine, trouble hearing, staggering walk, mental/mood changes (e.g., confusion, hallucinations, unusual behavior, trouble thinking clearly), tingling/numbness of hands/feet, unusual shakiness, increased sweating, increased hunger.

Tell your doctor immediately if any of these rare but very serious side effects occur: dizziness, chest pain, fainting, signs of heart failure (e.g., increasing tiredness, swelling of ankles/legs, shortness of breath), black/bloody stools, seizures.

A very serious allergic reaction to this drug is rare. However, seek immediate medical attention if you notice any symptoms of a serious allergic reaction, including: rash, itching, swelling, severe dizziness, trouble breathing.

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

Contact your doctor for medical advice about side effects. The following numbers do not provide medical advice, but in the US you may report side effects to the Food and Drug Administration (FDA) at 1-800-FDA-1088. In Canada, you may call Health Canada at 1-866-234-2345.

PRECAUTIONS: See also Warning section.

Before taking flucytosine, tell your doctor or pharmacist if you are allergic to it; or to fluorouracil; or if you have any other allergies.

This medication should not be used if you have certain medical conditions. Before using this medicine, consult your doctor or pharmacist if you have: end-stage kidney disease or are on kidney dialysis.

Before using this medication, tell your doctor or pharmacist your medical history, especially of: certain diseases of the blood cells/bone marrow (e.g., myelodysplastic syndrome, aplastic anemia, leukemia), low blood cell counts, recent radiation treatments, organ transplant, liver problems, diabetes, low blood minerals (e.g., potassium).

This drug may rarely make you dizzy or drowsy. Use caution while driving, using machinery, or doing any activity that requires alertness. Avoid alcoholic beverages.

Kidney function declines as you grow older. This medication is removed by the kidneys. Therefore, caution is advised when using this drug in the elderly because they may be more sensitive to the effects of the drug.

During pregnancy, this medication should be used only when clearly needed. Discuss the risks and benefits with your doctor.

It is not known whether this drug passes into breast milk. Consult your doctor before breast-feeding.

DRUG INTERACTIONS: Your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor or pharmacist first.

This drug should not be used with the following medication because very serious interactions may occur: cytosine arabinoside.

If you are currently using the medication listed above, tell your doctor or pharmacist before starting flucytosine.

Before using this medication, tell your doctor or pharmacist of all prescription and nonprescription/herbal products you may use, especially of: drugs that may decrease kidney function (e.g., amphotericin B, gentamicin, tobramycin), nonsteroidal anti-inflammatory drugs-NSAIDs (e.g., ibuprofen, naproxen, celecoxib), drugs that suppress the immune system (e.g., cancer chemotherapies, tacrolimus, cyclosporine).

Check the labels on all your medicines (e.g., cough-and-cold products) because they may contain NSAIDs.

This document does not contain all possible interactions. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you, and share the list with your doctor and pharmacist.

OVERDOSE: If overdose is suspected, contact your local poison control center or emergency room immediately. US residents can call the US National Poison Hotline at 1-800-222-1222. Canada residents can call a provincial poison control center.

NOTES: Do not share this medication with others.

Laboratory and/or medical tests (e.g., kidney function, blood cell counts, liver function, blood minerals) should be performed periodically to monitor your progress or check for side effects. Consult your doctor for more details.

MISSED DOSE: If you miss a dose, take it as soon as you remember. If it is near the time of the next dose, skip the missed dose and resume your usual dosing schedule. Do not double the dose to catch up.

STORAGE: Store at room temperature at 77 degrees F (25 degrees C) away from light and moisture. Brief storage between 59-86 degrees F (15-30 degrees C) is permitted. Do not store in the bathroom. Keep all medicines away from children and pets.

Do not flush medications down the toilet or pour them into a drain unless instructed to do so. Properly discard this product when it is expired or no longer needed. Consult your pharmacist or local waste disposal company for more details about how to safely discard your product.

Information last revised July 2008 Copyright(c) 2008 First DataBank, Inc.