Pharmacokinetics of ethylene glycol. III. Plasma disposition and metabolic fate after single increasing intravenous, peroral, or percutaneous doses in the male Sprague-Dawley rat.

1. The pharmacokinetic fate of [1,2-14C]-ethylene glycol (EG) was evaluated in the male Sprague-Dawley rat in order to characterize its overall uptake and elimination. Doses of 10 and 1000 mg/kg were administered by the intravenous (i.v.), peroral (p.o.), or percutaneous (p.c.) route; additional doses of 400, 600 and 800 mg/kg were evaluated by the p.o route. 2. Baseline data obtained by the i.v. route for bioavailability comparisons showed that while plasma radioactivity concentrations declined in a biexponential manner with t1/2 beta of 26-37 h, the disappearance of unmetabolized EG from the plasma was quite rapid (t1/2 beta of 0.8-1.2 h). Peroral doses were rapidly and almost completely absorbed, showing t1/2 abs in the order of minutes, and a bioavailable fraction for unmetabolized EG of 92-100%. Conversely, EG applied to rat skin was slowly and rather poorly absorbed, showing t1/2 abs which were an order of magnitude longer than for comparable p.o. and i.v. doses, and a bioavailability of approximately 22%. 3. The major route of elimination for the 10 mg/kg dose by any route was by metabolism to 14CO2 and exhalation, while urinary elimination of 14C was the secondary excretion pathway. 4. Plasma clearance of 14C was linear with increases in p.o. doses over the 400-800 mg/kg range, with AUC proportional to dose for these and the 10 mg/kg p.o. dose levels. However, a dose-dependent shift in excretion routes was observed following the p.o. 1000 mg/kg dose, with urine becoming the major excretion route, and similar capacity limited pharmacokinetics were observed for the i.v. 1000 mg/kg dose. Plasma pharmacokinetic data for unchanged EG after i.v. and p.o. doses demonstrated an apparent first-order kinetic behaviour between the 10 and 1000 mg/kg dose levels for the disappearance of EG. 5. Following both i.v. and p.o doses, dose-independent relationships were seen in the values obtained for the area under the plasma curve (AUC infinity), the total clearance of EG (CltotalEG), mean residence time (MRT infinity), apparent volume of distribution at steady state (Vdss), the terminal half-life (t1/2 beta) and the renal and metabolic clearance values. However, this dose-linear plasma time course was not apparent from the dose-dependent excretion profiles for these two exposure routes. 6. Increases in urinary 14C-glycolate were also observed when the i.v. or p.o. doses were increased from 10 to 1000 mg EG/kg, indicating that metabolism of EG makes a substantial contribution to AUC infinity in the beta disposition phase of the plasma curves for this high dose. Oxalate, a metabolite found in man after EG exposure, was detected at very low levels after both the 10 and 1000 mg/kg dose levels and by either i.v or p.o. routes. 7. Thus, EG given by three different routes demonstrated apparent first-order pharmacokinetic behaviour for disposition in and the elimination from plasma in the male rat, but dose-dependent changes occurred for the elimination of metabolites in urine and as 14CO2 after single i.v. and p.o. doses, but not for the p.c. routes.