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Active ingredient: Flucytosine - Brands, Medical Use, Clinical Data

Brands, Medical Use, Clinical Data

Drug Category

  • Antimetabolites
  • Antifungals

Dosage Forms

  • Capsule (250mg and 500mg)

Brands / Synonyms

5-FC; 5-Fluorocystosine; 5-Fluorocytosin; 5-Fluorocytosine; 5-Fluorocytosine (Flucytosine); 5-Flurocytosine; Ancobon; Ancobon (TN); Ancotil; Flucytosin; Flucytosine (JP14/USP); Flucytosine(USAN); Fluocytosine; Fluorcytosine

Indications

For the treatment (in combination with amphotericin B) of serious infections caused by susceptible strains of Candida (septicemia, endocarditis and urinary system infections) and/or Cryptococcus (meningitis and pulmonary infections).

Pharmacology

Flucytosine is an antimetabolite that acts as an antifungal agent with in vitro and in vivo activity against Candida and Cryptococcus. Flucytosine enters the fungal cell via cytosine permease; thus, flucytosine is metabolized to 5-fluorouracil within fungal organisms. The 5-fluorouracil is extensively incorporated into fungal RNA and inhibits synthesis of both DNA and RNA. The result is unbalanced growth and death of the fungal organism. Antifungal synergism between Ancobon and polyene antibiotics, particularly amphotericin B, has been reported.

Mechanism of Action

Although the exact mode of action is unknown, it has been proposed that flucytosine acts directly on fungal organisms by competitive inhibition of purine and pyrimidine uptake and indirectly by intracellular metabolism to 5-fluorouracil. Flucytosine enters the fungal cell via cytosine permease; thus, flucytosine is metabolized to 5-fluorouracil within fungal organisms. The 5-fluorouracil is extensively incorporated into fungal RNA and inhibits synthesis of both DNA and RNA. The result is unbalanced growth and death of the fungal organism. It also appears to be an inhibitor of fungal thymidylate synthase.

Absorption

Rapidly and virtually completely absorbed following oral administration. Bioavailability 78% to 89%.

Toxicity

Oral, rat: LD50 = >15 gm/kg.

Biotrnasformation / Drug Metabolism

Flucytosine is deaminated, possibly by gut bacteria or by the fungal targets, to 5-fluorouracil, the active metabolite.

Contraindications

5-Flucytosine should not be used in patients with a known hypersensitivity to the drug.

Drug Interactions

Cytosine arabinoside, a cytostatic agent, has been reported to inactivate the antifungal activity of flucytosine 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 Jaffe 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 Jaffe reaction.

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