Title: Flucytosine
CAS Registry Number: 2022-85-7
CAS Name: 4-Amino-5-fluoro-2(1H)-pyrimidinone
Additional Names: 5-fluorocytosine; 5-FC
Manufacturers' Codes: Ro-2-9915
Trademarks: Alcobon (Roche); Ancobon (Roche); Ancotil (Roche)
Molecular Formula: C4H4FN3O
Molecular Weight: 129.09
Percent Composition: C 37.22%, H 3.12%, F 14.72%, N 32.55%, O 12.39%
Literature References: Prepn: Duschinsky et al., J. Am. Chem. Soc. 79, 4559 (1957); Heidelberger, Duschinsky, US 2802005 (1957); Duschinsky, Heidelberger, US 2945038 and Duschinsky, US 3040026 (1960, 1962 both to Hoffmann-La Roche); Undheim, Gacek, Acta Chem. Scand. 23, 294 (1969). Patents as a fungicide: Berger, Duschinsky, BE 628615 and US 3368938 (1963, 1968 both to Hoffmann-La Roche). Activity studies: Grunberg et al., Antimicrob. Agents Chemother. 1963, 566; Shadomy et al., ibid. 1968, 452; Grunberg et al., in 5th Int. Congr. Chemother., Proc. vol. IV, K. Spitzy, Ed. (Verlag Wiener Med. Akad., 1967, Austria) p 69. Metabolic studies: Koechlin et al., Biochem. Pharmacol. 15, 435 (1966). Clinical results: Utz et al., Antimicrob. Agents Chemother. 1968, 344; Warner et al., ibid. 1970, 473. Comprehensive description: E. H. Waysek, J. H. Johnson, Anal. Profiles Drug Subs. 5, 115-138 (1976).
Properties: Odorless, white crystalline solid, mp 295-297° (dec). uv max (0.1N HCl): 285 nm (e 8900). Soly in water: 1.5 g/100 ml at 25°C. pKa1: 3.26. LD50 in mice (mg/kg): >2000 orally and s.c.; 1190 i.p.; 500 i.v. (Grunberg, 1963).
Melting point: mp 295-297° (dec)
pKa: pKa1: 3.26
Absorption maximum: uv max (0.1N HCl): 285 nm (e 8900)
Toxicity data: LD50 in mice (mg/kg): >2000 orally and s.c.; 1190 i.p.; 500 i.v. (Grunberg, 1963)
Therap-Cat: Antifungal.
Keywords: Antifungal (Synthetic).
Fludeoxyglucose F18 Fludiazepam Fludioxonil Fludrocortisone Flufenacet

Systematic (IUPAC) name
Clinical data
Trade names Ancobon
AHFS/Drugs.com monograph
MedlinePlus a601132
Pregnancy cat. B3 (AU) C (US)
Legal status POM (UK) -only (US)
Routes Oral, intravenous
Pharmacokinetic data
Bioavailability 75 to 90% (oral)
Protein binding 2.9 to 4%
Metabolism Minimal, in the GI tract
Half-life 2.4 to 4.8 hours
Excretion Renal (90%)
CAS number 2022-85-7 YesY
ATC code D01AE21 J02AX01
PubChem CID 3366
DrugBank DB01099
ChemSpider 3249 YesY
UNII D83282DT06 YesY
KEGG D00323 YesY
Chemical data
Formula C4H4FN3O 
Mol. mass 129.093 g/mol
 YesY (what is this?)  (verify)

Flucytosine, or 5-fluorocytosine, a fluorinated pyrimidine analogue, is a synthetic antimycotic drug.

It is structurally related to the cytostatic fluorouracil and to floxuridine. It is available in oral and in some countries also in injectable form. A common brand name is Ancobon. Flucytosine was first synthesized in 1957 but its antifungal properties were discovered in 1964. The drug is dispensed in capsules of 250 mg and 500 mg strength. The injectable form is diluted in 250 mL saline solution to contain 2.5 g total (10 mg/mL). The solution is physically incompatible with other drugs including amphotericin B.