Pharmacokinetics and bioavailability of diisopropanolamine (DIPA) in rats following intravenous or dermal application.

This study was conducted to determine the relative dermal bioavailability (absorption), distribution, metabolism, and excretion (ADME) of diisopropanolamine (DIPA), an alcohol amine used in a number of industrial and personal care products. Groups of 4 female Fischer 344 rats received either a single bolus i.v. dose of 19.0mg/kg (14)C-DIPA in water or a dermal application of 19.5mg/kg (14)C-DIPA in acetone to an area of 1cm(2) on the back and covered with a bandage. Time-course blood and excreta were collected and radioactivity determined. Urine was analyzed for DIPA and monoisopropanolamine (MIPA). Following i.v. administration, DIPA was rapidly cleared from the plasma and excreted into urine in a biexponential manner (t(1/2alpha), 0.4h; t(1/2beta), 2.9h). The levels of radioactivity in plasma dropped below the limit of detection 12h post-dosing. A total of 97+/-4% of the dose was actively excreted in urine by kidney, most ( approximately 71%) within 6h of dosing, virtually all as parent compound; renal clearance exceeded the glomerular filtration rate. Following dermal application, approximately 20% of the dose was absorbed in 48 h with the steady-state penetration rate of approximately 0.2%/h. Most (14.4%) of the applied radioactivity was excreted in urine at a relatively constant rate due to the presence of large amount of the (14)C-DIPA at the application site. Fecal elimination was <0.2% of the dose. The absorbed DIPA did not accumulate in tissues; only approximately 0.1% of the administered dose was found in liver and kidney. The absolute systemic dermal bioavailability (dose corrected AUC(dermal)/AUC(i.v.)) of (14)C-DIPA was 12%. The ADME of DIPA contrasts that of its diethanol analogue, diethanolamine, which displays a broad spectrum of toxicity in rats and mice. Toxicologically significant concentrations of DIPA are unlikely to be achieved in the systemic circulation and/or tissues as a result of repeated dermal application of products containing DIPA due to slow absorption from the skin, rapid unchanged elimination in urine, and majority of the products contain

Toxicity and pharmacokinetics of 2-(2-dimethylaminoethoxy)ethanol following cutaneous dosing.

A 9-day repeated cutaneous toxicity study in the New Zealand White rabbit was conducted using 6-h occluded contact with 0 (water control), 50, 250 and 500 mg dimethylaminoethoxyethanol (DMEE)/kg. There were no clinical signs, and no effects on body weight, food consumption or serum chemistry. Hematological effects were limted to increased leukocyte count due to heterophil leukocytosis, increased platelet count, and decreased hemoglobin and hematocrit at the high dose. These findings are typical of the response of cutaneous inflammation. Histopathological findings were limited to the DMEE-treated skin, and consisted of acanthosis and ulcerative/necrotizing dermatitis. Thus, there was no evidence for cumulative percutaneous systemic toxicity for DMEE. The pharmacokinetics of DMEE was investigated in the Fischer 344 rats. Rats were given an intravenous dose of 15 or 150 mg/kg, or an occluded cutaneous dose of 150 mg/kg [14C]DMEE, and its fate was followed for 48-72 h. DMEE was readily absorbed through the skin (bioavailability=72-80%). Concentration in plasma rose steadily to a maximum at about 3.5 h after dosing, and then declined in a biphasic manner. 14C-DMEE-derived radioactivity was distributed throughout the body, with no apparent sequestration in any particular organ. The highest concentrations were observed in the kidney, liver and lung, and the lowest concentrations were found in the brain and fat. Urine was the major route of excretion, with minor amounts eliminated in the feces and as expired CO(2). The rate of excretion was moderate, with about 30% of the applied dose eliminated in the first 12 h, and by 72 h after dosing, less than 4% of the dose remained in the carcass. Unchanged DMEE was the principal component detected in the urine. This observation, together with the less than 1% of the dose excreted as CO(2), showed that metabolism was not an important process in the elimination of DMEE in the rat.

Targeting acute ischemic stroke with a calcium-sensitive opener of maxi-K potassium channels.

During ischemic stroke, neurons at risk are exposed to pathologically high levels of intracellular calcium (Ca++), initiating a fatal biochemical cascade. To protect these neurons, we have developed openers of large-conductance, Ca++-activated (maxi-K or BK) potassium channels, thereby augmenting an endogenous mechanism for regulating Ca++ entry and membrane potential. The novel fluoro-oxindoles BMS-204352 and racemic compound 1 are potent, effective and uniquely Ca++-sensitive openers of maxi-K channels. In rat models of permanent large-vessel stroke, BMS-204352 provided significant levels of cortical neuroprotection when administered two hours after the onset of occlusion, but had no effects on blood pressure or cerebral blood flow. This novel approach may restrict Ca++ entry in neurons at risk while having minimal side effects.

Acute intravenous and inhalation pharmacokinetics of 2,4-pentanedione in the Fischer 344 rat.

2,4-Pentanedione (2,4-PD; CAS No. 123-54-6), an industrial chemical, was investigated for its comparative pharmacokinetics in male Fischer 344 rats by a single intravenous (i.v.) injection of (4.3, 43, 148.5, and 430 mg/kg), or a 6-hr nose-only inhalation exposure (400 ppm) to 14C-2,4-PD. For the i.v. route, the plasma concentration of 14C-2,4-PD-derived radioactivity declined in a biexponential fashion. The overall form of the 14C plasma concentration-time curves and derived pharmacokinetic parameters indicated that dose-linear kinetics occurred in the i.v. dose range 4.3-148.5 mg/kg, but not with 430 mg/kg. Metabolism of 2,4-PD was quite rapid as the concentration of unmetabolized 2,4-PD declined steadily to undetectable after 8 hr. 14C-2,4-PD derived radioactivity was eliminated mainly as 14CO2 and in urine. For the 4.3, 43 and 148.5 mg/kg doses 14CO2 elimination was relatively constant (36.8, 38.8 and 42.3% in 48 hr samples respectively) and greater than urinary excretion (17.9, 14.3 and 29.6%; 48 hr specimens). At 430 mg/kg i.v. there was a reversal of the excretion pattern, with urine 14C excretion (54.7%) becoming greater than that for 14CO2 (27.3%). Excretion in expired volatiles and feces was small. Radiochromatograms of urine showed free 2,4-PD in the 12 hr sample, together with 7 other metabolites. Free 2,4-PD and 6 of the metabolites decreased or were not detectable in a 24 or 48 hr urine sample, but one peak (retention 7.9 min) increased progressively to become the major fraction (97%). Nose-only exposure to 400 ppm 14C-2, 4-PD produced a mean decrease in breathing rate of 20.1%, which was constant and sustained throughout exposure, due to a lengthening of the expiratory phase of the respiratory cycle. 14C-2,4-PD was rapidly absorbed during the first 3 hr of exposure, then began to plateau, but did not reach a steady state. Postexposure elimination of 14C from plasma followed a biexponential form with a t1/2 for the terminal disposition phase of 30.72 hr. Plasma unmetabolized 2,4-PD was present throughout the whole of the exposure phase, but was significantly less than total 14C. Postexposure, plasma unmetabolized 2,4-PD declined rapidly to undetectable concentrations by 12 hr. Radiolabel excretion was approximately equivalent in urine (37.6%) and expired 14CO2 (36.3%). Urine radiochromatograms showed a minor 2,4-PD contaminant (0.6-5.9% over 48 hr), along with 7 other peaks probably representing metabolites. As with the 148.5 mg/kg i.v. dose, the major metabolite peak was at 7.8 min retention, increasing from 41.1% (12 hr) to 62.8% (48 hr). Immediately postexposure, radioactivity was present in all tissues examined, but on a concentration basis (microgram equiv/g) there was no preferential accumulation of 14C in any tissue or organ. On a total organ basis, highest contents were in liver and kidney, presumably related to the metabolism and excretion of 2,4-PD. By 48 hr postexposure, concentrations had decreased in all tissues except fat, presumably due to the lipophilicity of 14C residues. The profile of the plasma-time radioactivity curves, and the presence of residual radioactivity in tissues at 48 hr postexposure, suggests that a cumulative process could occur with frequent repeated exposures.

Chlorhexidine gluconate (CHG) activity against clinical isolates of vancomycin-resistant Enterococcus faecium (VREF) and the effects of moisturizing agents on CHG residue accumulation on the skin.

The effectiveness of skin decontamination by chlorhexidine gluconate (CHG) in the presence of commonly-used skin moisturizing lotions was evaluated using vancomycin-resistant Enterococcus faecium (VREF) as a representative nosocomial pathogen. Anti-bacterial efficacy was determined in vitro using pigskin preparations inoculated with five VREF clinical isolates to evaluate Calgon Vestal 2 and 4% (by weight) CHG solutions in comparison with Hibiclens Antiseptic Antimicrobial Cleaner (4% CHG solution). Control inocula were determined for each experiment from recovery of VREF harvested directly from the surface of each control piece of skin. These CHG formulations were evaluated in the presence and absence of Calgon Vestal 'Lotion Soft Skin Conditioner' (LSSC) to determine potential interactions of CHG with LSSC, and also with ¿Vaseline Intensive Care' lotion as a CHG-deactivating agent. The 2% Calgon Vestal CHG alone reduced VREF 10(2)-10(3)-fold, as well as 10(3)-10(4)-fold when LSSC was present, and was as efficacious as either 4% CHG solution when these were tested in the presence of LSSC. Four percent Calgon Vestal CHG produced reductions of 10(3)-10(5)-fold with or without LSSC present. Conversely, ¿Hibiclens' showed similar reductions in the presence of LSSC to that for the Calgon Vestal 4% CHG, but only a 10(1)-10(3)-fold reduction without LSSC. ¿Vaseline Intensive Care' lotion completely inactivated the VREF-killing effects for all of the CHG formulations tested, while LSSC and ¿Vaseline Intensive Care' lotion both showed minimal activity alone against these VREF isolates. These results indicate that the Calgon Vestal 2% CHG solution is as effective against VREF, even in the presence of LSSC, as either the 4% Calgon Vestal or Hibiclens 4% CHG formulations; the use of this lower concentration of CHG may be associated with less irritation, particularly with concomitant use of LSSC.

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.

A tiered approach to pharmacokinetic studies.

Studies of absorption, distribution, metabolism, and elimination (ADME) have long been recognized as important in the evaluation of the pharmacological efficacy of pharmaceutical agents. In recent years, the importance of ADME studies in toxicology also has become increasingly apparent. In realization of the importance of ADME studies, regulatory agencies have established guidelines governing the conduct of these studies. To be of maximum utility, it is desirable that ADME and pharmacokinetic studies be closely integrated with the toxicity testing protocol. However, in many instances this is not the case, which results in ADME and pharmacokinetic studies that are often chronologically and philosophically remote from the toxicity testing protocols. An inevitable consequence of this approach is that it frequently leads to the generation of ADME data that are of limited use in the process of toxicity evaluation and risk assessment. Recently, there has been increased focus on developing testing strategies that would result in the development of ADME data with greater application to toxicity testing and risk assessment. An example of such an approach is the concept of a tiered approach to the conduct of ADME studies. An important aspect of the tiered approach is generating ADME data at an earlier stage during the toxicity testing of a chemical. This could be effected by acceptance of the concept of a minimum experimental data set for a chemical. This minimum data set could be conducted in a timely and economic manner and would develop data addressing three fundamental questions: Is the chemical absorbed? Is the chemical metabolized? Does the chemical persist?(ABSTRACT TRUNCATED AT 250 WORDS)

The use of pharmacokinetics as an interpretive and predictive tool in chemical toxicology testing and risk assessment: a position paper on the appropriate use of pharmacokinetics in chemical toxicology.

It has been recognized for several decades in the pharmaceutical industry that the safety evaluation of pharmacological agents must include pharmacokinetic (PK) studies, which are designed to determine the rate of absorption, distribution, metabolism, and excretion (ADME). In recent years the importance of such ADME studies in toxicology has also become increasingly apparent to the chemical industry. This increased focus has led to testing strategies that can produce ADME/PK data with greater applicability to toxicity testing and risk assessment. An example of such a strategy is the concept of a tiered approach to the conduct of ADME/PK studies (Wilson, A. G. E., Frantz, S. W., and Keifer, L. C. (1994). Environ. Health Perspect., in press). However, in practice, PK data are often viewed as being of limited usefulness and of only ancillary importance to the determination of chemical toxicity. As a consequence, the close integration of PK studies with toxicity-testing protocols is not always practiced within the chemical industry and is thus frequently scheduled independently from toxicity testing. This lack of integration has resulted in the design of subchronic (13-week) and chronic (2-year) toxicity studies without the benefit of PK information to establish the appropriate dose levels to be used, often because of inappropriate timing. The result is that much of the PK data which have been generated is without a clear consideration of its application to toxicity testing and risk assessment. This position paper is intended to provide recommendations for the appropriate design and interpretation of a PK study, as well as when and how to use PK data in the interpretation of toxicology data. Additional issues discussed in the paper include the design of PK studies to evaluate tissue time-course relationships and chemical persistence, the overall usefulness of PK data to toxicology testing, and the utility of PK as a useful interpretive and predictive tool in toxicology and risk assessment.

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.

Mutagenicity in Salmonella assays of cyclohexane epoxide derivatives.

15 Cyclohexane epoxide derivatives were synthesized and compared for direct mutagenicity and bacterial toxicity using Salmonella typhimurium strain TA100 in the liquid suspension and spot-test version of the Ames procedure. While no general correlations could be established for position and stereochemistry of the hydroxylated derivatives, an increase in mutagenicity was noted for the presence of electron-withdrawing groups and unsaturation in conjugation with the oxirane groups.

Tetrachloroethylene: balance and tissue distribution in male Sprague-Dawley rats by drinking-water administration.

While low levels of organic contaminants have been reported to occur in drinking water, often little information is available concerning the toxicological significance of ingestion by this route. For tetrachloroethylene, considerable animal toxicity data exist for gavage or inhalation exposure. Since extrapolation of toxicity between routes of administration implies similar pharmacokinetic disposition, the pharmacokinetics of tetrachloroethylene was examined in rats following administration in the drinking water. Tetrachloro[14C]ethylene was administered to adult, male Sprague-Dawley rats in saturated drinking water solutions (approximately 150 ppm) resulting in a mean dose of 8.1 +/- 3.1 mg/kg. Within 72 hr from termination of a 12-hr drinking exposure period, approximately 88% of the body burden was eliminated as unmetabolized parent compound in expired air. As much as 96% of the activity recovered in this form was excreted during the first 24 hr. The remaining 14C activity recovered was the result of metabolic conversion to 14CO2 (2.2%), nonvolatile metabolites in urine (7.2%) and feces (1.7%), and minor amounts (0.9%) in the carcass. Radioactivity in the carcass 72 hr following termination of the exposure period was distributed within liver, kidneys, fat, lungs, heart, and adrenals. Pulmonary elimination of unchanged tetrachloroethylene was monophasic with a calculated elimination half life of 7.1 hr. The elimination kinetics were consistent with results previously generated by both gavage and inhalation exposure. The fate of tetrachloroethylene following drinking-water administration was not substantially different from the disposition resulting from these two routes of administration.

Bacterial mutagenicity and toxicity of cycloaliphatic epoxides.

The mutagenicity of 12 cycloaliphatic epoxides was investigated using the Ames Salmonella assay without the addition of liver homogenate fractions. Base-pair substitution mutagenic activity was detected for 8 members of this series of compounds, confirming our laboratory's previous observations of weak mutagenic response at high dose levels for cis-1,2-disubstituted epoxides. While mutagenicity decreased with expanding ring size, inhibition of bacterial growth increased for increases in ring size. Toxicity accompanying the required high doses for the demonstration of mutagenicity for these compounds prevented the establishment of meaningful dose-response ranges for the remaining epoxides tested. The volatility observed with these oxiranes also made dose-response establishment difficult but was countered by the use of petri dish sealing bands during incubation. Mutagenicity in this series was found to be generally more pronounced in TA1535 while toxicity was detected with greater sensitivity by TA100. The use of the less permeable strains TA92, TA1950 and TA2410, all having normal lipopolysaccharide cell wall coatings, failed to reduce this marked toxicity. The repair test compared results in TA1535 (repair-deficient strain) with TA1975 (repair-proficient strain) and demonstrated that the bacteria were not being killed by damage to DNA since toxicity was not reduced in TA1975.