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Flucytosine

Flucytosine, a fluorinated pyrimidine analogue, is a synthetic antimycotic drug. Chemically it is referred to as 4-amino-5-fluoro-2(1H)-pyrimidinon. The sum formula is C4H4FN3O. Fucytosine has the CAS-Number 2022-85-7. It is structurally related to the cytostatic flourouracil and to floxuridine. It is available in oral and in some countries also in injectable form. A common brand name is Ancobon®. The drug is dispensed in capsules of 250 mg and 500 mg strength. The injectable form is diluted in 250ml NaCl-solution to contain 2.5 grams totally (10mg per ml). more...

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The solution is physically incompatible with other drugs including Amphotericin B.

Pharmacology

Mechanisms of action

Two major mechanisms of acton have been elucidated, one is that the drug is intrafungally converted into the cytostatic flourouracil that undergoes further steps of activation and finally interacts as 5-fluorouridinetriphosphate with RNA-biosynthesis and disturbs therefore the building of certain essential proteins. The other mechanism is the conversion into 5-flourodeoxyuridinemonophosphate which inhibits fungal DNA-synthesis.

Spectrum of susceptible fungi and Resistance

Flucytosine is as well in vitro and in vivo active against some strains of Candida and Cryptococcus. Limited studies demonstrate that Flucytosine may be of value against infections with Sporothrix, Aspergillus, Cladosporium, Exophila, and Phialophora. Resistance is quite commonly seen as well in treatment naive patients and under current treatment with Flucytosine. In different strains of Candida resistance has been noted to occur in 1 to 50% of all specimen obtained from patients.

Pharmacokinetic data

Flucytosine is well absorbed (75 to 90%) from the GI-Tract. Intake with meals slows the resorption, but does not decrease the amount resorbed. Following an oral dose of 2 grams peak serum levels are reached after approximately 6 hours. The time to peak level decreases with continued therapy. After 4 days peak levels are measured after 2 hours. The drug is eliminated renally. In normal patients Flucytosine has reportedly a half-life of 2.5 to 6 hours. In patients with impared renal function higher serum levels are seen and the drug tends to cumulate in these patients. The drug is mainly excreted unchanged in the urine (90% of an oral dose) and only traces are metabolized and excreted in the feces. Therapeutic serum levels range from 25 to 100mcg/ml. Serum levels in exceed of 100mcg are associated with a higher incidence of side-effects. Periodic measurements of serum levels are recommended for all patients and are a must in patients with renal damage.

Human overdose

Symptoms and their severities are unknown, because Flucytosine is used under close medical supervision, but expected to be an excess of the usually encountered side-effects on bone-marrow, GI-Tract, liver, and kidney-function. Vigouros hydration and hemodialysis may be helpful to remove the drug from the body. Hemodialysis is particular useful in patients with impaired renal function.

Human carcinogenity

It is not known, if Flucytosine is a human carcinogen. The issue has been raised because traces of 5-fluorouracil, which is a known carcinogen, are found in the colon resulting from the metabolization of Flucytosine.

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Flucytosine 10-mg/mL Oral Liquid
From International Journal of Pharmaceutical Compounding, 3/1/04

METHOD OF PREPARATION

1. Calculate the required quantity of each ingredient for the total amount to be prepared.

2. Accurately measure each ingredient. Ohtain the required number of Ancobon (flucytosine) 250-mg or 500-mg capsules to provide the flucytosine for this preparation.

3. Reinove the contents from the capsules, and pulverize the powder.

4. Add the glycerin and form a smooth paste.

5. Tn portions, incorporate the Ora-Plus and mix well.

6. Add sufficient Ora-Sweet or Ora-Sweet SF to volume and mix well.

7. Package and label.

PACKAGING

Package in tight, light-resistant containers.1

LABELING

Keep out of reach of children. Use only as directed. Shake well before using.

STABILITY

A beyond-use date of 60 days is appropriate for this preparation.1-2

USE

Flucytosine is used as an antifungal agent.

QUALITYCONTROL

Quality-control assessment can include weight/volume, pH, specific gravity, active-drug assay, color, rheological properties/pourability, physical observation and physical stability (discoloration, foreign materials, gas formation and mold growth).3

DISCUSSION

Flucytosine (C^sub 4^H^sub 4^FN^sub 3^O, MW 129.09) occurs as a white to offwhite crystalline powder that is odorless or has a slight odor. It is sparingly soluble in water and slightly soluble in alcohol. Flucytosine is a fluorinated pyrimidine analog that is used to treat serious infections caused by susceptible strains of Candida or Cryptococcus neoformans and to treat chromomycosis caused by susceptible fungi.1,4

Glycerin (C^sub 3^H^sub 8^O^sub 3^, MW 92.1, glycerol, 1,2,3-propane triol) occurs as a clear, colorless, odorless, viscous, hygroscopic liquid with a taste about two thirds as sweet as that of sucrose. It is miscible with water, methanol and 95% ethanol; practically insoluble in oils and chloroform and slightly soluble in acetone. It should be stored in airtight containers in a cool place. It is not prone to oxidation but will decompose on heating. When mixed with water, ethanol and propylene glycol, the mixtures are chemically stable.5

Ora-Plus is an oral suspending vehicle that accepts dilution of up to 50% or more with water, flavoring agents or syrups and still retains its suspending properties. It has a pH of approximately 4.2 and an osmolality of about 230 mOsm/Kg. It is a thixotropic vehicle with a viscosity of approximately 1000 cps at 25┬░C. It contains purified water, microcrystalline cellulose, sodium carboxymethylcellulose, xanthan gum, carrageenan, sodium phosphate and citric acid as buffering agents; simethicone as an antifoaming agent; and potassium sorbate and methylparaben as preservatives.6

Ora-Sweet syrup is a flavoring vehicle for oral extemporaneous preparations. It is flavored with a citrus-berry flavor blend and contains glycerin and sorbitol to prevent "cap-lock," a problem associated with many syrups. It is buffered to a pH of approximately 4.2 and has an osmolality of about 3240 mOsm/Kg. It contains purified water, sucrose, glycerin, sorbitol (5%), flavoring, sodium phosphate and citric acid as buffering agents and potassium sorbate and methylparaben as preservatives.6

Ora-Sweet SF is a flavoring vehicle for oral extemporaneous preparations. It is a sugar-free, alcohol-free syrup flavored with a citrus-berry flavor blend. It is buffered to a pH of approximately 4.2 and may be used alone or in combination with other vehicles. It will tolerate dilution up to 50% with dissolved actives in water or suspending agents and still retain an acceptable taste. It has an osmolality of 2150 mOsm/Kg. It contains water, sodium saccharin, xanthan gum, glycerin, sorbitol, citric acid and sodium citrate as buffers; methylparaben, propylparaben and potassium sorbate as preservatives; and flavoring agents.6

REFERENCES

1. US Pharmacopeial Convention, Inc. United States Pharmacopeia 26NationalFormulary 21. Rockville, MD:US Pharmacopeial Convention, lnc.;2003:794-795, 2197-2201, 2561.

2. Alien LV Jr, Erickson MA. Stability of acetazolamide, allopurinol, azathioprine, clonazepam and flucytosine in extemporaneously compounded oral liquids. Am J Health Syst Pharm 1996;53:1944-1949.

3. Alien LV Jr. Standard operating procedure for performing physical quality assessment of oral and topical liquids. /JPC1999;3:146-147.

4. McEvoy GK. AHFS Drug Information-2003. Bethesda, MD:American Society of Health-System Pharmacists;2003:102.

5. Price JC. Glycerin. In :Rowe RC, Sheskey PJ, Weller PJ, eds. Handbook of Pharmaceutical Excipients. 4th ed. Washington, DC:American Pharmaceutical Association;2003:257-259.

6. Ora-Plus/Ora-Sweet/Ora-Sweet SF [product information]. Minneapolis, MN:Paddock Laboratories, Inc.

Copyright International Journal of Pharmaceutical Compounding Mar/Apr 2004
Provided by ProQuest Information and Learning Company. All rights Reserved

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