title: Pharmacokinetic study of doxifluridine given by 5-day stepped-dose infusion.
abstract: Doxifluridine (5'-deoxy-5-fluorouridine, 5'-dFUR) metabolism has been reported to be saturable and associated with a fall in clearance of the drug as the dose is increased. The aim of the present study was to determine the disposition of 5'-dFUR and 5-fluorouracil (5-FU) when 5'-dFUR was given as a 5-day infusion, with the infusion rate increased stepwise every 24 h. Measurement of plasma and urinary levels of 5'-dFUR and 5-FU at steady state for each infusion rate enabled the estimation of 5'-dFUR renal (ClR) and nonrenal (ClNR) clearance and 5-FU renal clearance. A total of 28 patients with histologically proven malignancy received 5-day courses of 5'-dFUR ranging in dose from 3.75 to 20 g/m2 per 120 h. The lowest dose given over 24 h was 0.25 g/m2, and the highest was 5 g/m2. Steady-state plasma levels of 5'-dFUR ranged from 167 to 6,519 ng/ml. At these plasma levels there was no evidence of significant saturation of 5'-dFUR metabolism; steady-state plasma levels of 5'-dFUR increased approximately linearly with dose, and nonrenal clearance did not change significantly with dose. There was also no evidence of nonlinearity in 5'-dFUR renal clearance. The mean (+/- SD) ClR of 5'-dFUR was 108.9 +/- 53.6 ml/min per m2 (range, 45.7-210 ml/min per m2), and the ClNR was 728 +/- 181 ml/min per m2 (range, 444-1,119 ml/min per m2). Renal clearance comprised 13% of the total 5'-dFUR clearance. The mean renal clearance of 5-FU was 100.8 +/- 48.6 ml/min per m2 (range, 23.5-198 ml/min per m2). There was considerable interpatient variability in 5'-dFUR renal and nonrenal clearance, even at the same dose level. We concluded that the administration of 5'-dFUR by the infusion method described avoided the saturation of nonrenal elimination processes reported to occur with shorter infusion schedules.
authors: Department of Clinical Pharmacology, Queen Elizabeth Hospital, Adelaide, South Australia.
authors: P A
authors: PA
authors: Reece
authors: I N
authors: IN
authors: Olver
authors: R G
authors: RG
authors: Morris
authors: J F
authors: JF
authors: Bishop
authors: T W
authors: TW
authors: Guentert
authors: H S
authors: HS
authors: Hill
authors: B L
authors: BL
authors: Hillcoat
mesh_terms: D000328:Adult; D000368:Aged; D000970:Antineoplastic Agents / Q000008:administration & dosage / Q000009:adverse effects / Q000493:pharmacokinetics*; D004334:Drug Administration Schedule; D005260:Female; D005467:Floxuridine / Q000008:administration & dosage / Q000009:adverse effects / Q000493:pharmacokinetics*; D005472:Fluorouracil / Q000493:pharmacokinetics; D006801:Humans; D007262:Infusions, Intravenous; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000188:drug therapy*
chemical_list: D000970:Antineoplastic Agents; D005467:Floxuridine; D005472:Fluorouracil; C025034:doxifluridine