Pharmacokinetics of ethylene glycol. II. Tissue distribution, dose-dependent elimination, and identification of urinary metabolites following single intravenous, peroral or percutaneous doses in female Sprague-Dawley rats and CD-1 mice.

1. [1,2]-14C-Ethylene glycol (EG) was given to female CD (Sprague-Dawley) rats and CD-1 mice in order to determine tissue distribution and metabolic fate after intravenous (iv), peroral (po), and percutaneous (pc) doses. Rats were given doses of 10 or 1000 mg/kg by each route, and additional pc doses of 400, 600 or 800 mg/kg. Mice were also given iv and po doses of 10 or 1000 mg/kg, and intermediate po doses of 100, 200 or 400 mg/kg. Mice were given po doses of 100 or 1000 mg/kg, and both species were given a 50% (w/w) aqueous po dose to simulate antifreeze exposure. 2. For both species, EG is very rapidly and almost completely adsorbed after po doses. Perorally administered EG doses produced similar dose-dependent relationships described in prior studies for the disposition and excretion of iv doses. 3. The tissue distribution of EG following either iv or po routes was essentially the same, with similar percentages recovered for each dose by both routes and for either species. 4. Cutaneously-applied EG was slowly and rather poorly adsorbed in both species, in comparison with po-dose administration, and urinalysis after undiluted po doses indicated that EG probably penetrates rat skin in the parent form. There was an absence in both species of dose-dependent changes in disposition and elimination following the pc application of EG. 5. 14C-labelled EG, glycolic acid and/or oxalic acid accounted for the majority of the detectable radioactivity in the urine samples from all dose routes in the rat, while glycoaldehyde and glyoxylic acid were not detected in any of the urine fractions evaluated. Similar increases in glycolate production with increasing dose were also observed in mouse urine samples from iv and po dosing. Also, glyoxylate and oxalate were absent from mouse urine. 6. Oxidative metabolic pathways appeared to be saturated at high po doses in both species, resulting in a shift from principally 14CO2 exhalation to urinary 14C excretion, while the onset of capacity-limited metabolic changes appears to occur at lower doses for mice than for rats. 7. In summary, rats and mice displayed several similarities in the manner in which low doses of EG by several routes are distributed, metabolized, and excreted, but the onset of capacity-limited changes in metabolism occurs at lower doses for mice than for rats. Such differences in the disposition of EG may provide important interpretive information to help explain differences observed in developmental toxicity and nephrotoxic responses between these two rodent species.

Pharmacokinetics of ethylene glycol. I. Plasma disposition after single intravenous, peroral, or percutaneous doses in female Sprague-Dawley rats and CD-1 mice.

The pharmacokinetics of [1,2-14C]ethylene glycol (EG) were evaluated in female Sprague-Dawley rats and CD-1 mice to characterize the plasma disposition after intravenous (IV), peroral (PO), and percutaneous (PC) doses. Rats were given doses of 10 or 1000 mg/kg by each route, and additional PO doses of 400, 600, or 800 mg/kg. Mice were also given IV and PO (bolus gavage) doses of 10 or 1000 mg/kg, and additional PO doses of 100, 200, or 400 mg/kg. PC doses in mice were 100 or 1000 mg/kg, and both species were given a 1000 mg/kg PC dose with a 50% (w/w) aqueous solution (2 ml/kg) to simulate antifreeze exposure. Results from this study have shown that orally-administered EG is very rapidly and almost completely absorbed in both rats and mice, with a bioavailable fraction of 92-100% in rats and similar percentages at the higher doses in mice. In contrast, the absorption of cutaneously applied EG is comparatively slow in both species. A species difference in the overall absorption of PC doses was demonstrated, with higher recoveries of 14C observed after PC doses in mice than for rats and a greater penetration of 14C after applying a 50% aqueous PC dose in mice than in rats, as evidenced by quantifiable plasma 14C concentrations only in mice. The major metabolites in both rats and mice are CO2 and glycolate. Oxidative metabolic pathways are saturated at high PO doses in both species, resulting in a shift from exhaled CO2 as the major excretion route to urinary excretion. The capacity to metabolize more completely EG to CO2 at low doses seems to be greater in the mouse than in the rat, as evidenced by the absence of urinary oxalate from EG-dosed female mice, and saturation of metabolic pathways at a comparatively lower dose in mice than for rats. This evidence suggests that dose-dependent changes in EG excretion in female Sprague-Dawley rats and CD-1 mice probably resulted from capacity-limited effects on EG metabolic pathways for the production of CO2 and a compensatory urine clearance of glycolate. Results from the present study corroborate previous observations in rats for the lower doses, but demonstrate a substantial difference in single-dose pharmacokinetics for IV and PO 1000 mg/kg doses in mice vs. rats. In summary, these data indicate that mice show a nonlinear plasma disposition of total radioactivity (EG and its metabolites) as dose is increased, whereas in rats plasma kinetics were linear over the dose range evaluated, whereas excretion kinetic patterns were nonlinear in both species as dose is increased.

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.

Pharmacokinetics of 2-ethyl-1,3-hexanediol. III. In vitro skin penetration comparisons using the excised skin of humans, rats, and rabbits.

Excised skin from Fischer 344 rats, New Zealand White rabbits, and human females (obtained from mammoplasty patients) were compared for their in vitro skin penetration potential with 2-[14C]-ethyl-1,3-hexanediol (EHD). EHD was applied as both an undiluted dose and a 3% v/v aqueous dose using a flowthrough skin penetration chamber design and was analyzed over 0-6 hr. The undiluted dose was equivalent to a 150 mg/kg dose used in vivo with rats (Frantz et al., Drug Metab. Dispos. 20(1), 6-18, 1992), but normalized on a per cm2 surface area basis, and applied under occluded conditions (covered as for in vivo studies). Undiluted applications of EHD did not substantially penetrate skin, with effluent recoveries of approximately 0.9% of the applied dose for human skin, 2-4% for rat skin, and 3-6% for rabbit skin. By comparison, nonoccluded human skin showed lower effluent radioactivity (0.6%), which was attributed to EHD evaporation from skin. With undiluted EHD, approximately 97% of the recovered 14C was an unabsorbed dose for human skin, with 94% for rat skin and 85% for rabbit skin (expressed as a percentage of the recovered dose). Based on HPLC analysis of effluent samples, 99-100% of the undiluted [14C]EHD penetrated rat, rabbit, and human skin in the unmetabolized form. In contrast, approximately 5% of the applied aqueous dose was recovered in the effluents for human skin, while 6-9% appeared in effluents for rat skin; rabbit skin was not evaluated for aqueous doses. The fraction of unabsorbed aqueous EHD dose totaled 53% of the applied dose for human skin and 63% for rat skin. Evaporative loss of undiluted [14C]EHD was also measured (captured on activated charcoal) in separate experiments and compared with a known standard chemical, N,N[14C]diethyl-m-toluamide (DEET). Evaporation of EHD was clearly a competing factor with penetration, particularly for human skin preparations, and evaporative losses were similar to those seen in previous studies. Penetration of skin was also greater for both EHD and DEET when evaporation was not permitted (stopped chamber). Permeability constant (kp) values were calculated using the pseudo steady-state slopes from plots for cumulative mg/cm2 penetration vs time. For undiluted EHD, human skin had the slowest penetration rate, while rabbit skin kp values were the largest. The kp values for water solutions of EHD on rat and human skin demonstrated a slightly higher penetration, with values of the same order of magnitude as that observed for a concurrently run [14C]ethanol control. The minimal skin penetration observed in vitro in this study, taken together with in vivo percutaneous pharmacokinetic studies (Frantz et al., 1992) and the known percutaneous toxicology of EHD, suggests that penetration through human skin and systemic adverse effects should be minimal.

Disposition and metabolism of acrylic acid in C3H mice and Fischer 344 rats after oral or cutaneous administration.

Acrylic acid (AA) is used in large amounts to produce acrylic esters and polymers. Here we report on the disposition and metabolism of [1-14C]AA in male C3H mice and Fischer 344 (F344) rats after oral (40 and 150) mg/kg) or cutaneous (10 and 40 mg/kg) administration. Although these and other strains of rodents have been used frequently in toxicity studies of AA, results of pharmacokinetic studies are available for only the Sprague-Dawley rat. In the current study, C3H mice rapidly absorbed and metabolized orally administered AA, with about 80% of the dose exhaled as 14CO2 within 24 h. Excretion in urine and feces accounted for approximately 3% and 1% of the dose, respectively. Elimination of 14C from plasma, liver, and kidney was rapid but was slower from fat. The disposition of orally administered AA in F344 rats was similar to the results obtained from mice. After cutaneous administration to C3H mice, about 12% of the dose was absorbed, while the remainder apparently evaporated. Approximately 80% of the absorbed fraction of the dose was metabolized to 14CO2 within 24 h. Excretion in urine and feces each accounted for less than 0.5% of the dose. Elimination of radioactivity from plasma, liver, and kidney was rapid; however, levels in fat were higher at 72 h than at 1 or 8 h. After cutaneous administration to F344 rats, 19-26% of the dose was absorbed, and the rest apparently evaporated. Disposition of the absorbed fraction of the dose was similar to results found in mice. Results from an in vitro experiment with rat skin showed that at least 60% of the applied dose evaporated and about 25% was absorbed, confirming the in vivo results. High-performance liquid chromatography (HPLC) analysis of rat urine and rat and mouse tissues indicated that absorbed AA was rapidly metabolized by the beta-oxidation pathway of propionate catabolism. In summary, rapid detoxification of systemically absorbed AA, as observed here in C3H mice and F344 rats, can explain findings that AA causes minimal systemic toxicity despite its causing irritation at portal-of-entry tissues.

Pharmacokinetics of 2-ethyl-1,3-hexanediol. II. Nonsystemic disposition following single percutaneous or peroral doses in Fischer 344 rats.

The pharmacokinetics of [1,3-14C]-2-ethyl-1,3-hexanediol (EHD) were investigated following single percutaneous doses of 150 mg/kg, applied to male and female Fischer 344 rats, or single peroral doses of 1.5 or 150 mg EHD/kg given by gavage to male Fischer 344 rats. EHD-derived radioactivity was slowly absorbed through skin and relatively rapidly excreted through the urine in a first-order manner over 48 hr postdosing. Skin penetration of 14C was sufficiently slow that the terminal rate constant for the plasma concentration data had to be derived from the absorption phase of this curve, based on the terminal rate constant for a comparable intravenous dose plasma curve [Frantz et al.: Drug Metab. Dispos. 19, 881 (1991)]. Plasma data from perorally doses rats exhibited dose-linearity over a 1.5-150 mg/kg range, with plasma 14C concentration vs. time plots for oral doses of EHD resembling the iv time-course data. This resulted from a very rapid absorption phase (5.5 min t1/2), with plasma 14C levels for both dose levels decreasing in a biexponential manner. The major route of excretion after peroral doses was in urine, making this mode of excretion consistent for both routes of administration evaluated in this study and including the doses given in previous iv work. Kinetic analysis confirmed that this route of excretion was first-order. HPLC analysis of urine from both routes demonstrated that EHD was metabolized and excreted as at least two major, water-soluble urinary metabolites; these metabolites were not identified in this investigation. No unmetabolized EHD was detected in urine, indicating that EHD may be completely metabolized in the rat. Overall, EHD was absorbed, distributed, metabolized, and eliminated from the Fischer rat in a first-order manner following either cutaneous or peroral doses. The results of this study indicate that the kinetic patterns observed experimentally will be dose-proportional for doses administered in the range of 1.5-150 mg/kg.

Pharmacokinetics of 2-ethyl-1,3-hexanediol. I. Systemic disposition following single intravenous doses in male Fischer 344 rats.

A determination of the systemic pharmacokinetics of [1,3-14C]-2-ethyl-1,3-hexanediol (EHD) was conducted following i.v. dosing of male Fischer 344 rats. Pharmacokinetic analyses of the plasma data indicated that there is dose linearity in the 1.5 to 150 mg/kg range, and that EHD is cleared from plasma in a biexponential manner according to first order transfer and elimination processes. The data show that EHD-derived radioactivity is very rapidly distributed and then is slowly eliminated (probably as EHD metabolites) over a 48-hr period after a single i.v. injection. EHD is not found in the urine as unchanged test material by HPLC analysis following these i.v. doses, indicating that this chemical is probably completely metabolized in the rat. The appearance of EHD-derived radioactivity in the urine also follows a first order behavior, as evidenced by calculations of rate constants which are similar to the terminal rate constants from plasma radioactivity data. Both U infinity-Ut and dU/dt analyses of urine radioactivity data demonstrated that first order rate constants can be derived from urinary excretion data and supported the overall conclusion that the elimination of EHD from the rat follows first order processes in this range of i.v. doses.

Biochemical and morphological studies on the percutaneous uptake of [14C] ethylenediamine in the rat.

Male Wistar rats were exposed to aqueous [14C]ethylenediamine (EDA) solutions (10, 25, or 50%) percutaneously over a 7 x 7 cm area on the back with occlusion for 24 h. For each rat dosed, three types of studies were conducted: (1) plasma kinetics, (2) material balance, and (3) histological evaluation, including autoradiography of the skin sample from the dosing area. Adequate kinetic measurements were obtained only from animals treated with 25 and 50% EDA, but not from the 10% treatment group, due to analytical limitations. The uptake of [14C]EDA percutaneously by the rat was relatively slow in comparison with uptake following peroral or endotracheal administration. The absorption of EDA by the animals was estimated to be greater than 61, 55, and 12%, respectively, for the 50, 25, and 10% treatment groups. A large portion (11-32%) of the dose was left on/in the dosing area. Urinary excretion was the predominant route for the disposition of EDA. The recovery of the administered dose was low (70-83%), possibly due to volatilization of EDA from the skin during dosing and holding. Histologic examination of skin sections (dosing areas) revealed a normal, intact epidermis in rats dosed with 10% EDA, but full-thickness epidermal necrosis in rats dosed with 25% or 50% EDA solutions. The damage of the epidermis apparently enhanced the penetration of EDA. Autoradiographic preparations revealed a concentration of the [14C]EDA radiolabel over the keratin layer and hair shafts.

Age-dependent pharmacokinetic changes of ethylenediamine in Fischer 344 rats parallel to a two-year chronic toxicity study.

As part of a 2-year chronic toxicity study, the pharmacokinetics of ethylenediamine (EDA) was studied in Fischer 344 rats of both sexes at day zero (naive animals), 6 months (controls and high level animals), and 18 months (controls and high level animals). The rats, which were randomized along with the rest of the animals on the toxicity study, were taken for pharmacokinetic experiments at the specified time. A single per os (po) dose of 50 mg [14C]EDA X 2HCl/kg was given to each rat and the plasma kinetics was followed for a 24-hr period. Five pharmacokinetic parameters (absorption rate constant, terminal half-life, area under the curve, volume of distribution, and 14CO2 production rate constant) were compared with respect to age, sex, and chronic dosing. There were no apparent age-, sex-, and/or chronic dosing-related differences in absorption rate constant and terminal half-life. However, age-related changes in area under the curve (AUC) were evident. The older rats had higher values (generally two- to threefold) for AUC than the younger rats. This age-related difference in AUC is closely associated with the volumes of distribution (Vd) of the animals of varying ages. On the basis of liters per kilogram, the Vd's of the older rats are approximately one-fourth to one-half of those for the younger (zero day) rats. The 14CO2 production rate constant was derived from the rate of formation of 14CO2 as a result of [14C]EDA X 2HCl dosing. The comparison of this constant under the various experimental conditions suggests sex-related differences.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolism of carbaryl by kidney, liver, and lung from human postembryonic fetal autopsy tissue.

Metabolic profiles of carbaryl in human postembryonic fetal autopsy tissue were determined using an in vitro tissue-maintenance technique. 1-Naphthyl-14C or N-methyl-14C-carbaryl was applied to growth medium containing explants of the tissue. Each mixture was incubated for 18 hr and the medium analyzed by DEAE-cellulose column chromatography. Fetal liver performed the metabolic processes of demethylation, hydrolysis, hydroxylation, and oxidation, followed by conjugation, as was found with adult liver. However, the anionics from fetal liver amounts to 20% of those found with adult liver. The kidney made naphthyl glucuronide and naphthyl sulfate, whereas the lung produced naphthyl sulfate from carbaryl. The metabolic activities of the fetal kidney and lung were close to the corresponding human adult tissues based upon the anionic metabolites found and the amount of unmetabolized carbaryl in the medium after 18 hr of incubation. Silica gel chromatography of ether-extractable neutral fractions from DEAE-cellulose revealed 3,4, and 9 ether-extractable metabolites from lung, kidney, and liver, respectively. The present study shows that the in vitro technique is capable of semiquantitatively demonstrating the metabolic activities of specific organs from the human fetus.