title: Pharmacokinetics, oral bioavailability, and metabolic disposition in rats of (-)-cis-5-fluoro-1-[2-(hydroxymethyl)-1,3-oxathiolan-5-yl] cytosine, a nucleoside analog active against human immunodeficiency virus and hepatitis B virus.
abstract: The pharmacokinetics and metabolism of the potent anti-human immunodeficiency virus and anti-hepatitis B virus compound, (-)-cis-5-fluoro-1-[2-(hydroxymethyl)-1,3-oxathiolan-5-yl] cytosine (FTC), were investigated in male CD rats. Plasma clearance of 10 mg of FTC per kg of body weight was biexponential in rats, with a half-life at alpha phase of 4.7 +/- 1.1 min (mean +/- standard deviation) and a half-life at beta phase of 44 +/- 8.8 min (n = 5). The total body clearance of FTC was 1.8 +/- 0.1 liters/h/kg, and the oral bioavailability was 90% +/- 8%. The volume of distribution at steady state (Vss) was 1.5 +/- 0.1 liters/kg. Increasing the dose to 100 mg/kg slowed clearance to 1.5 +/- 0.2 liters/kg/h, lowered the Vss to 1.2 +/- 0.2 liters/kg, and reduced the oral bioavailability to 65% +/- 15%. FTC in the brains of rats was initially less than 2% of the plasma concentration but increased to 6% by 2 h postdose. Probenecid elevated levels of FTC in plasma as well as in brains but did not alter the brain-to-plasma ratio. The urinary and fecal recoveries of unchanged FTC after a 10-mg/kg intravenous dose were 87% +/- 3% and 5% +/- 1.6%, respectively. After a 10-mg/kg oral dose, respective urinary and fecal recoveries were 70% +/- 2.5% and 25% +/- 1.6%. Two sulfoxides of FTC were observed in the urine, accounting for 0.4% +/- 0.03% and 2.7% +/- 0.2% of the intravenous dose and 0.4% +/- 0.06% and 2.5% +/- 0.3% of the oral dose. Also observed were 5-fluorocytosine, representing 0.4% +/- 0.06% of the intravenous dose and 0.4% +/- 0.07% of the oral dose, and FTC glucuronide, representing 0.7% +/- 0.2% of the oral dose and 0.4% +/- 0.2% of the intravenous dose. Neither deaminated FTC nor 5-fluorouracil was observed in the urine (less than 0.2% of dose). The high oral availability and minimal metabolism of FTC encourage its further preclinical development.
authors.affiliation: Wellcome Research Laboratories, Research Triangle Park, North Carolina 27709, USA.
authors.forename: L W
authors.initials: LW
authors.lastname: Frick
authors.forename: L
authors.initials: L
authors.lastname: St John
authors.forename: L C
authors.initials: LC
authors.lastname: Taylor
authors.forename: G R
authors.initials: GR
authors.lastname: Painter
authors.forename: P A
authors.initials: PA
authors.lastname: Furman
authors.forename: D C
authors.initials: DC
authors.lastname: Liotta
authors.forename: E S
authors.initials: ES
authors.lastname: Furfine
authors.forename: D J
authors.initials: DJ
authors.lastname: Nelson
mesh_terms: D000284:Administration, Oral; D000818:Animals; D000998:Antiviral Agents / Q000378:metabolism / Q000493:pharmacokinetics* / Q000494:pharmacology; D001682:Biological Availability; D001711:Biotransformation; D001921:Brain / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D000068679:Emtricitabine / Q000031:analogs & derivatives; D015497:HIV-1 / Q000187:drug effects*; D006207:Half-Life; D006515:Hepatitis B virus / Q000187:drug effects*; D006801:Humans; D007275:Injections, Intravenous; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D013056:Spectrophotometry, Ultraviolet; D014018:Tissue Distribution; D016047:Zalcitabine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000493:pharmacokinetics / Q000494:pharmacology
chemical_list: D000998:Antiviral Agents; D016047:Zalcitabine; D000068679:Emtricitabine; C075889:Racivir