Physiological disposition of 2,2'-anhydro-1-beta-D-arabinofuranosyl-5-fluorocytosine in humans.
[2-14C]-2,2'-Anhydro-1-beta-D-arabinofuranosyl-5-fluorocytosine ([14C]AAFC) was given to 7 patients i.v. and to 3 patients p.o. at doses of 2 or 20 mg/kg. After i.v. administration of [14C]AAFC, 20 mg/kg, maximum plasma levels of up to 42.5 mug [14C]AAFC equivalents per ml of plasma occurred. A rapid exponential decrease of the radioactivity resulted in an initial half-line of 0.5 to 1.5 hr for the first part and a half-line of 8 to 24 hr for the second part of the curve. Most of the radioactivity was unchanged starting material. In plasma, 1-beta-D-arabinofuranosyl-5-fluorocytosine was found for only a short time and at low levels after i.v. injection. Its deamination product, 1-beta-D-arabinofuranosyl-5-fluorouracil (AFU), too, showed up in minor quantities. A small amount of 2,2'-anhydro-1-beta-D-arabinofuranosyl-5-fluorouracil was also detected. Administration p.o. of the 14C-labeled drug (2 mg/kg) resulted in the slow appearance of radioactivity in plasma. It peaked at 6 to 18 hr and slowly disappeared with a half-life of 12 to 18 hr. In a fasting patient, [14C]AAFC, 20 mg/kg, administered p.o. resulted in its rapid absorption into the bloodstream and in elevated levels in plasma for 48 hr. The unchanged drug and AFU were the predominant substances identified in plasms. Radioactivity after i.v. injection was found primarily in urine; only small amounts were recovered in expired air (to 2.4%) and traces were found in feces. The predominant urinary excretions product was the unchanged drug (average, 79%). The rest was AFU (average, 12.4%), 1-beta-D-arabinofuranosyl-5-fluorocytosine (average, 3.9%), and 2,2'-anhydro-1-beta-D-arabinofuranosyl-5-fluorouracil (average, 1.9%). After p.o. administration of the labeled drug, the calculated absorption was 32%. Urine contained about 50% unchanged drug and 40% AFU; the remainder was composed of 1-beta-D-arabinofuranosyl-5-fluorocytosine and the deaminated anhydro compound, 2,2'-anhydro-1-beta-D-arabinofuranosyl-5-fluorouracil. The rate of excretion in the urine was slow. In general after both i.v. and p.o. administration, spinal fluid contained considerably less radioactivity than plasma at shor intervals after the administration. At longer intervals after i.v. and p.o. administration, spinal fluid contained comparable or even considerably higher levels of radioactivity when compared to the levels in plasma. Autopsies performed 6 to 25 days after i.v. or p.o. drug administration revealed that radioactivity remained in kidney, spleen, small intestine, liver, and lung.
D000284:Administration, Oral; D003561:Cytarabine / Q000031:analogs & derivatives* / Q000097:blood / Q000378:metabolism; D003641:Deamination; D005215:Fasting; D005243:Feces / Q000032:analysis; D005461:Fluorine; D006207:Half-Life; D006801:Humans; D007275:Injections, Intravenous
D003561:Cytarabine; D005461:Fluorine