PHARMACOKINETICS OF ETHYLENE-GLYCOL .3. PLASMA DISPOSITION AND METABOLIC-FATE AFTER SINGLE INCREASING INTRAVENOUS, PERORAL, OR PERCUTANEOUSDOSES IN THE MALE SPRAGUE-DAWLEY RAT
Sw. Frantz et al., PHARMACOKINETICS OF ETHYLENE-GLYCOL .3. PLASMA DISPOSITION AND METABOLIC-FATE AFTER SINGLE INCREASING INTRAVENOUS, PERORAL, OR PERCUTANEOUSDOSES IN THE MALE SPRAGUE-DAWLEY RAT, Xenobiotica, 26(5), 1996, pp. 515-539
1. The pharmacokinetic fate of [1,2-C-14]-ethylene glycol (EG) was eva
luated in the male Sprague-Dawley rat in order to characterize its ove
rall uptake and elimination. Doses of 10 and 1000 mg/kg were administe
red 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 th
e p.o. route. 2. Baseline data obtained by the i.v. route for bioavail
ability comparisons showed that while plasma radioactivity concentrati
ons declined in a biexponential manner with t(1/2)(beta) of 26-37 h, t
he disappearance of unmetabolized EG from the plasma was quite rapid (
t(1/2)(beta) of 0.8-1.2 h). Peroral doses were rapidly and almost comp
letely absorbed, showing t(1/2)(beta) in the order of minutes, and a b
ioavailable fraction for unmetabolized EG of 92-100%. Conversely, EG a
pplied to rat skin was slowly and rather poorly absorbed, showing t(1/
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 m
etabolism to (CO2)-C-14 and exhalation, while urinary elimination of C
-14 was the secondary excretion pathway. 4. Plasma clearance of C-14 w
as linear with increases in p.o. doses over the 400-800 mg/kg range, w
ith AUC proportional to dose for these and the 10 mg/kg p.o. dose leve
ls. However, a dose-dependent shift in excretion routes was observed f
ollowing the p.o. 1000 mg/kg dose, with urine becoming the major excre
tion route, and similar capacity limited pharmacokinetics were observe
d for the i.v. 1000 mg/kg dose. Plasma pharmacokinetic data for unchan
ged 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 di
sappearance of EG. 5. Following both i.v. and p.o. doses, dose-indepen
dent relationships were seen in the values obtained for the area under
the plasma curve (AUG,), the total clearance of EG (Cl-total(EG)), me
an residence time (MRT(infinity)), apparent volume of distribution at
steady slate (Vd(SS)), the terminal half-life (t(1/2)(beta)) and the r
enal and metabolic clearance values. However, this dose-linear plasma
time course was not apparent from the dose-dependent excretion profile
s for these two exposure routes. 6. Increases in urinary C-14-glycolat
e were also observed when the i.v. or p.o. doses were increased from 1
0 to 1000 mg EG/kg, indicating that metabolism of EG makes a substanti
al contribution to AUC(infinity) in the beta disposition phase of the
plasma curves for this high dose. Oxalate, a metabolite found in man a
fter EG exposure, was detected at very low levels after both the 10 an
d 1000 mg/kg dose levels and by either the i.v. or p.o. routes. 7. Thu
s, EG given by three different routes demonstrated apparent first-orde
r pharmacokinetic behaviour for disposition in and the elimination fro
m plasma in the male rat, but dose-dependent changes occurred for the
elimination of metabolites in urine and as (CO2)-C-14 after single i.v
. and p.o. doses, but not for the p.c. routes.