Trichloroethylene Hypersensitivity Syndrome Is Potentially Mediated through Its Metabolite Chloral Hydrate.

BACKGROUND: We documented previously the entity of trichloroethylene (TCE) hypersensitivity syndrome (THS) in occupational workers. OBJECTIVES: To identify the culprit causative compound, determine the type of hypersensitivity of THS, and establish a screening test for subjects at risk of THS. METHODS: TCE and its main metabolites chloral hydrate (CH), trichloroethanol (TCOH) and trichloroacetic acid (TCA) were used as allergens at different concentrations in skin patch tests. The study included 19 case subjects diagnosed with occupational THS, 22 control healthy workers exposed to TCE (exposure >12 weeks), and 20 validation new workers exposed to TCE for <12 weeks free of THS. All subjects were followed-up for 12 weeks after the patch test. RESULTS: The highest patch test positive rate in subjects with THS was for CH, followed by TCOH, TCA and TCE. The CH patch test positive rate was 100% irrespective of CH concentrations (15%, 10% and 5%). The TCOH patch test positive rate was concentration-dependent (89.5%, 73.7% and 52.6% for 5%, 0.5% and 0.05%, respectively). Lower patch test positive rates were noted for TCA and TCE. All patch tests (including four allergens) were all negative in each of the 22 control subjects. None of the subjects of the validation group had a positive 15% CH patch test. CONCLUSIONS: Chloral hydrate seems to be the culprit causative compound of THS and type IV seems to be the major type of hypersensitivity of THS. The CH patch test could be potentially useful for screening workers at risk of THS.

Pharmacokinetic interaction between methotrexate and chloral hydrate.

We report the case of a drug interaction between methotrexate (MTX) and chloral hydrate (CH) observed in a child treated for acute leukemia. Significantly slower MTX clearance and increased MTX exposure occurred on the first three courses of a high-dose chemotherapy when co-administered with CH despite normal renal function, adequate hydration, and alkalinization. Mean MTX area under the curve associated with CH administration was 1,134 µmol hours/L, compared to 608 µmol hours/L after discontinuation of CH. This interaction possibly resulted from a competition between anionic CH metabolites and MTX for renal tubular excretion.

Effects of temperature, surfactants and skin location on the dermal penetration of haloacetonitriles and chloral hydrate.

Dermal exposure has been recognized as an important contributor to the total internal dose to disinfection-by-products (DBPs) in water. However, the effect of the use of surfactants, water temperature and area of the body exposed to DBPs on their dermal flux has not been characterized and was the focus of the present study using an in-vitro system. The dermal flux of mg/l concentrations of haloacetonitriles and chloral hydrate (CH), important cytotoxic DBPs, increased by approximately 50% to 170% with increasing temperature from 25 °C to 40 °C. The fluxes for the torso and dorsum of the hand were much higher than that of palm and scalp skin. An increase in flux was observed for chloroacetonitrite and dichloroacetonitrile, two less lipophilic HANs, but not for trichloroacetonitrile or CH, with the addition of 2% sodium lauryl sulfate or 2% sodium laureth sulfate, two surfactants commonly used in soaps and shampoos used in showering and bathing. Thus, factors such as temperature, surfactants and skin location affect dermal penetration and should be considered when evaluating dermal absorption.

Percutaneous absorption of haloacetonitriles and chloral hydrate and simulated human exposures.

Disinfection-by-products (DBPs) have long been a human health concern and many are known carcinogens and teratogens. Skin is exposed to DBPs in water through bathing and swimming; however, dermal uptake of many DBPs has not been characterized. The present studies were initiated to measure the permeation coefficients (K(p) ) for haloacetonitriles (HANs) and chloral hydrate (CH), important cytotoxic DBPs. The K(p) values measured using fully hydrated dermatomed torso skin at 37 °C for the HANs ranged from 0.099 to 0.17 cm h⁻¹, and was 0.0039 cm h⁻¹ for CH. Of the HANs, dibromoacetonitrile had the highest permeability while chloroacetonitrile had the lowest permeability and a direct relationship was observed between their K(p) and their octanol/water partition coefficients (K(ow) ). The K(p) values of the HANs were also approximately 30 times that of CH. The monthly dermal and ingestion doses of HANs and CH of an average American population were estimated using Monte Carlo simulations. The dermal doses of HANs from showering and bathing ranged from 0.39 to 0.78 times their ingestion doses but only approximately 0.02 times their ingestion doses for CH, assuming that the K(p) values determined are applicable to shorter water contact times. However, that ratio can vary markedly with chlorinated swimming pool exposures, with a range of 0.30-2.3 for HANs and 0.19-0.25 for CH. Dermal exposure to HANs and CH seems to be a significant route of exposure and should be considered when evaluating their total exposure during the routine usage of water for bathing and swimming.

[Clopidogrel and its salts: any clnical implication?]. / Le clopidogrel et ses differents sets: existe-t-il une pertinence clinique?

Clopidogrel hydrogen sulfate is an antiplatelet agent administered, alone or in combination with acetyl salicylic acid, approved in the prevention of cardiovascular events based on large-scale clinical trials. The new salt formulations clopidogrel where approved based on pharmacokinetic measurements of the inactive prodrug on few healthy volunteers, without any other medication. Clopidogrel hydrogen sulfate has a wide variability in platelet response and the pharmacokinetic of the active metabolite is not dose-linear. Ideally, new clopidogrel salts should be tested for therapeutic equivalence in the target patient population. Should this not be feasible, consistent bioequivalence data should be obtained for the active metabolite, using a properly validated and standardized test method.

Kinetics of chloral hydrate and its metabolites in male human volunteers.

Chloral hydrate (CH) is a short-lived intermediate in the metabolism of trichloroethylene (TRI). TRI, CH, and two common metabolites, trichloroacetic acid (TCA) and dichloroacetic acid (DCA) have been shown to be hepatocarcinogenic in mice. To better understand the pharmacokinetics of these metabolites of TRI in humans, eight male volunteers, aged 24-39, were administered single doses of 500 or 1,500 mg or a series of three doses of 500 mg given at 48 h intervals, in three separate experiments. Blood and urine were collected over a 7-day period and CH, DCA, TCA, free trichloroethanol (f-TCE), and total trichloroethanol (T-TCE=trichloroethanol and trichloroethanol-glucuronide [TCE-G]) were measured. DCA was detected in blood and urine only in trace quantities (<2 microM). TCA, on the other hand, had the highest plasma concentration and the largest AUC of any metabolite. The TCA elimination curve displayed an unusual concentration-time profile that contained three distinct compartments within the 7-day follow-up period. Previous work in rats has shown that the complex elimination curve for TCA results largely from the enterohepatic circulation of TCE-G and its subsequent conversion to TCA. As a result TCA had a very long residence time and this, in turn, led to a substantial enhancement of peak concentrations following the third dose in the multiple dose experiment. Approximately 59% of the AUC of plasma TCA following CH administration is produced via the enterohepatic circulation of TCE-G. The AUC for f-TCE was found to be positively correlated with serum bilirubin concentrations. This effect was greatest in one subject that was found to have serum bilirubin concentrations at the upper limit of the normal range in all three experiments. The AUC of f-TCE in the plasma of this individual was consistently about twice that of the other seven subjects. The kinetics of the other metabolites of CH was not significantly modified in this individual. These data indicate that individuals with a more impaired capacity for glucuronidation may be very sensitive to the central nervous system depressant effects of high doses of CH, which are commonly attributed to plasma levels of f-TCE.

Bayesian population analysis of a harmonized physiologically based pharmacokinetic model of trichloroethylene and its metabolites.

Bayesian population analysis of a harmonized physiologically based pharmacokinetic (PBPK) model for trichloroethylene (TCE) and its metabolites was performed. In the Bayesian framework, prior information about the PBPK model parameters is updated using experimental kinetic data to obtain posterior parameter estimates. Experimental kinetic data measured in mice, rats, and humans were available for this analysis, and the resulting posterior model predictions were in better agreement with the kinetic data than prior model predictions. Uncertainty in the prediction of the kinetics of TCE, trichloroacetic acid (TCA), and trichloroethanol (TCOH) was reduced, while the kinetics of other key metabolites dichloroacetic acid (DCA), chloral hydrate (CHL), and dichlorovinyl mercaptan (DCVSH) remain relatively uncertain due to sparse kinetic data for use in this analysis. To help focus future research to further reduce uncertainty in model predictions, a sensitivity analysis was conducted to help identify the parameters that have the greatest impact on various internal dose metric predictions. For application to a risk assessment for TCE, the model provides accurate estimates of TCE, TCA, and TCOH kinetics. This analysis provides an important step toward estimating uncertainty of dose-response relationships in noncancer and cancer risk assessment, improving the extrapolation of toxic TCE doses from experimental animals to humans.

Pharmacodynamics of chloral hydrate in former preterm infants.

UNLABELLED: The aim of this study was to document the pharmacodynamics of chloral hydrate in former preterm infants at term post-conception age. The degree of sedation (COMFORT), feeding behaviour and cardiorespiratory events (bradycardic events, apnoeas) before and after administration of chloral hydrate (oral, 30 mg/kg) were prospectively evaluated in former preterm infants during procedural sedation. Characteristics at birth, during neonatal stay and at inclusion were collected. Paired Wilcoxon and McNemar tests were used to study the impact of chloral hydrate. Characteristics of infants who displayed severe bradycardic events were compared to infants in whom no bradycardic events were recorded (Mann Whitney U, Fischer's exact). A significant increase in sedation (decrease COMFORT scale) was observed up to 12 h after administration. There was a minor but significant decrease in oral intake (161 to 156 ml/kg/day, P < 0.01). A significant increase in the number of bradycardic events (<80/min: 38 to 82 events, of which < 70/min: 30 to 79 of which < 60/min: 15 to 45; at least P < 0.01) and in the duration of the most severe bradycardic event (8-12.5 s) was observed. Therefore, further inclusion was stopped when 26 neonates were included. Infants who displayed severe bradycardic (< 60/min) events ( n = 13) after administration of chloral hydrate had a lower gestational age at birth without difference in post-conception age at inclusion. CONCLUSION: Chloral hydrate was associated with an increase in unintended side-effects in former preterm infants, likely reflecting population specific pharmacodynamics and kinetics of chloral hydrate.

Toxicokinetics of chloral hydrate in ad libitum-fed, dietary-controlled, and calorically restricted male B6C3F1 mice following short-term exposure.

Chloral hydrate is widely used as a sedative in pediatric medicine and is a by-product of water chlorination and a metabolic intermediate in the biotransformation of trichloroethylene. Chloral hydrate and its major metabolite, trichloroacetic acid, induce liver tumors in B6C3F1 mice, a strain that can exhibit high rates of background liver tumor incidence, which is associated with increased body weight. This report describes the influence of diet and body weight on the acute toxicity, hepatic enzyme response, and toxickinetics of chloral hydrate as part of a larger study investigating the carcinogenicity of chloral hydrate in ad libitum-fed and dietary controlled mice. Dietary control involves moderate food restriction to maintain the test animals at an idealized body weight. Mice were dosed with chloral hydrate at 0, 50, 100, 250, 500, and 1000 mg/kg daily, 5 days/week, by aqueous gavage for 2 weekly dosing cycles. Three diet groups were used: ad libitum, dietary control, and 40% caloric restriction. Both dietary control and caloric restriction slightly reduced acute toxicity of high doses of chloral hydrate and potentiated the induction of hepatic enzymes associated with peroxisome proliferation. Chloral hydrate toxicokinetics were investigated using blood samples obtained by sequential tail clipping and a microscale gas chromatography technique. It was rapidly cleared from serum within 3 h of dosing. Trichloroacetate was the major metabolite in serum in all three diet groups. Although the area under the curve values for serum trichloroacetate were slightly greater in the dietary controlled and calorically restricted groups than in the ad libitum-fed groups, this increase did not appear to completely account for the potentiation of hepatic enzyme induction by dietary restriction.

[Mixed fatal poisoning caused by taking L-methadone and chloral hydrate]. / Letale Mischintoxikation durch Zufuhr von L-Methadon und Chloralhydrat.

A 42-year-old female drug user who was enrolled in a methadone maintenance program was found dead in her apartment. Cause of death was an intoxication with chloral hydrate and L-methadone. Trichloroethanol (TCE), the primary metabolite of chloral hydrate, was quantified by solid phase microextraction (SPME) and GC/MS in heartblood (27 micrograms/ml) and urine (338 micrograms/ml). D- and L-methadone were differentiated by chiral HPLC, which showed that only L-methadone had been taken. The quantitation of L-methadone and its metabolite EDDP was carried out by GC/MS from heartblood (1300 ng/ml and 86 ng/ml, respectively), urine (5239 ng/ml and 4960 ng/ml, respectively) and gastric contents (159 ng/ml and 122 ng/ml, respectively). The concentrations of both--trichloroethanol and methadone--were in toxic ranges.

[Chloral hydrate: a hypnotic best forgotten?]. / L'hydrate de chloral, un hypnotique à oublier?

Synthesised by Justin Liebig in 1832 chloral hydrate is one of the oldest synthetic agents. Since 1869 it has been in use for hypnotic or sedative purposes. Chloral hydrate was used a lot from the end of the 19th century to the middle of the 20th century. Since then chloral hydrate has been less frequently in use as a hypnotic. In the 1990's, the principal use of chloral hydrate in pediatrics was the sedation of children for minor surgery during dental or diagnostic procedures. In general practice, it is an analgesia found in topical preparations. It was known as safe and easy to use. Now it is shown to be potentially dangerous (risk of death in case of intoxication) and there is doubt about genotoxicity and carcinogenecity. The pharmacological property was known in 1948 when Butler discovered the principal active metabolite, trichloroethanol. The gastro-intestinal tract rapidly absorbs chloral hydrate after oral or rectal use. The sedative and hypnotic effects appear in 20 to 60 minutes. The main metabolites [trichloroethanol (TCE) and trichloroacetic acid (TCA)] are formed by hepatocytes and erythrocytes. The half-life of chloral hydrate is short (a few minutes), the half lives of the metabolics are longer, 8 to 12 hours for TCE and 67 hours for TCA. The affinity for lipids is high. It is eliminated principally by the kidneys. Its mechanism of action is unknown. It is a depressor of the SNC, and the sedation is attributed to chloral hydrate and the hypnotic effect to TCE. The interactions appear with: alcohol, anticoagulants, amitriptyline and furosemide. The use of flumazenil (a gaba antagonist), in case of intoxication, indicates a possible action of GABA. The posology is usually between 0.5 to 2 g per day. Chloral hydrate is taken during meals to prevent gastric irritation. The main side effects are digestive, cardiologic (risk of rhythm disorder), dermatologic, neuropsychiatric (withdrawn, delusions, hallucination, dependence) and ophthalmologic. Death occurs after absorption of doses of around 10 g of hydrate chloral, some cases were reported with 5 g. The use of hydrate chloral is contra-indicated in cases of gastric ulcers, hepatic insufficiency, porphyry, respiratory insufficiency, association with anticoagulants and hyper sensibility. Nowadays should we be using chloral hydrate in cases of insomnia in adult and older people? A recent preclinical working group of the French Agency for evaluation of medicinal products reassessed the benefit/risk ratio of chloral hydrate. Many references are found about genotoxicity and carcinogenicity in recent literature. In France, since the end of 2000, chloral hydrate has been withdrawn from many medications for external use in dermatology and in stomatology. Chloral hydrate can be used as a pediatric sedative only once in a lifetime. The psychiatric indication for insomnia is no longer justified and especially in older people.

Effect of enterohepatic circulation on the pharmacokinetics of chloral hydrate and its metabolites in F344 rats.

Chloral hydrate (CH) is a commonly found disinfection by-product in water purification, a metabolite of trichloroethylene, and a sedative/hypnotic drug. CH and two of its reported metabolites, trichloroacetic acid (TCA) and dichloroacetic acid (DCA), are hepatocarcinogenic in mice. Another metabolite of CH, trichloroethanol (TCE), is also metabolized into TCA, and the enterohepatic circulation (EHC) of TCE maintains a pool of metabolite for the eventual production of TCA. To gain insight on the effects of EHC on the kinetics of CH and on the formation of TCA and DCA, dual cannulated F344 rats were infused with 12, 48, or 192 mg/kg of CH and the blood, bile, urine, and feces were collected over a 48-h period. CH was cleared rapidly (>3000 ml/h/kg) and displayed biphasic elimination kinetics, with the first phase being elimination of the dose and the second phase exhibiting formation rate-limited kinetics relative to its TCE metabolite. The effects of EHC on metabolite kinetics were only significant at the highest dose, resulting in a 44% and 17% decrease in the area under the curve (AUC) of TCA and TCE, respectively. The renal clearance of CH, free TCE (f-TCE), and TCA of 2, 2.7, and 38 ml/h/kg, respectively, indicates an efficient reabsorption mechanism for all of these small chlorinated compounds. DCA was detected at only trace levels (<2 microM) as a metabolite of CH, TCA, or TCE.

NTP technical report on the toxicity and metabolism studies of chloral hydrate (CAS No. 302-17-0). Administered by gavage to F344/N rats and B6C3F1 mice.

Chloral hydrate is widely used as a sedative and a hypnotic in pediatric medicine. It is also a byproduct of water chlorination. Chloral hydrate has been shown to be genotoxic in numerous prokaryotic and eukaryotic assay systems including human lymphocytes in vitro. One of its metabolites, trichloroacetic acid, has demonstrated hepatocarcinogenic activity in mice. Trichloroethylene and perchloroethylene, both of which are metabolized to chloral hydrate, have been shown to be carcinogenic in rats and/or mice. Because of this evidence of carcinogenicity and because of the wide-spread use of chloral hydrate, 16- or 17-day range-finding toxicity studies and separate 16- or 17-day metabolism studies were performed in F344/N rats and B6C3F1 mice in preparation for further long-term rodent studies. In addition, in vitro studies of the metabolism and DNA-binding capacity of chloral hydrate and its metabolites were performed. Genetic toxicity studies were conducted in Salmonella typhimurium, cultured Chinese hamster ovary cells, Drosophila melanogaster, and mouse bone marrow cells. For the range-finding studies, groups of eight male and eight female F344/N Nctr BR rats and B6C3F1/Nctr BR (C57BL/6N x C3H/HeN MTV-) mice were administered 0, 50, 100, 200, 400, or 800 mg chloral hydrate per kg body weight in water by gavage 5 days per week for 17 days (rats) or 16 days (mice) for a total of 12 doses. One male rat receiving 800 mg/kg died after five doses. Two 800 mg/kg female rats died after dosing ended but before study termination. One male mouse in each group except the 400 mg/kg group died before the end of the study. Two 800 mg/kg female mice also died before the end of the study. The final mean body weight of 800 mg/kg male rats and the mean body weight gains of 400 and 800 mg/kg males were significantly less than those of the vehicle controls. The mean body weight gains of all groups of dosed male mice were significantly greater than that of the vehicle control group. The only clinical finding in rats and mice attributed to chloral hydrate treatment was light sedation in the 400 mg/kg groups and heavy sedation in the 800 mg/kg groups; sedation subsided within 30 minutes or 3 hours, respectively. The liver weights of 400 mg/kg male mice and 800 mg/kg male and female mice were significantly greater than those of the vehicle control groups. No chemical-related lesions were observed in rats or mice. Male and female rats and mice were administered a single dose of 50 or 200 mg chloral hydrate per kg body weight in water by gavage, or 12 doses of 50 or 200 mg/kg over 17 days (rats) or 16 days (mice). Plasma concentrations of chloral hydrate and its metabolites were determined 15 minutes, 1, 3, 6, and 24 hours, and 2, 4, 8, and 16 days after receiving 1 or 12 doses. Maximum concentrations of chloral hydrate were observed at the initial sampling point of 15 minutes. By 1 hour, the concentrations had dropped substantially, and by 3 hours, chloral hydrate could not be detected in rats or mice. Trichloroacetic acid was the major metabolite detected in the plasma. In rats, the concentrations rose slowly, with the peaks occurring between 1 and 6 hours after treatment. In mice, the peak concentrations were found 1 hour after dosing. The concentrations then slowly decreased such that by 2 days the metabolite could no longer be detected in rats or mice. Trichloroethanol was assayed both as the free alcohol and its glucuronide. In rats, the maximum concentrations of free trichloroethanol occurred at 15 minutes, while the peak concentrations of trichloroethanol glucuronide were found at 1 hour; by 3 hours, concentrations of both metabolites approached background levels. In mice, the maximum concentrations of both metabolites occurred at 15 minutes, and by 1 to 3 hours concentrations approached background levels. The plasma concentrations of chloral hydrate and its metabolites were dose dependent in rats and mice. In mice, plasma concentrations of trichloroacetic acid were significantly higher after a single dose than after 12 doses. None of the metabolic parameters appears to account for species differences that may exist in hepatocarcinogenicity. The data from the study of metabolism and DNA adduct formation indicated that in vitro metabolism of 200 microM to 5 mM chloral hydrate by male B6C3F1 mouse liver microsomes (control microsomes) generated free radical intermediates that resulted in endogenous lipid peroxidation, forming malondialdehyde, formaldehyde, acetaldehyde, acetone, and propionaldehyde. Similar concentrations of trichloroacetic acid and trichloroethanol, the primary metabolites of chloral hydrate, also generated free radicals and induced lipid peroxidation. Lipid peroxidation induced by trichloroacetic acid nearly equaled that induced by chloral hydrate, while that from trichloroethanol was three- to fourfold less. Metabolism of 200 microM to 5 mM chloral hydrate, trichloroacetic acid, and trichloroethanol by liver microsomes of B6C3F1 mice pretreated with pyrazole (pyrazole-induced microsomes) yielded lipid peroxidation products at concentrations two- to threefold greater than those from liver microsomes of untreated mice. Additionally, chloral hydrate-induced lipid peroxidation catalyzed by control and pyrazole-induced microsomes was reduced significantly by 2,4-dichloro-6-phenylphenoxyethylamine, a general cytochrome P450 inhibitor. Human lymphoblastoid transgenic cells expressing cytochrome P(450)2E1 metabolized 200 to 5,000 micrograms/mL chloral hydrate to reactants inducing mutations, whereas the parental cell line was inactive. The malondialdehyde-modified DNA adduct, 3-(2-deoxy-beta-D-erythro-pentofuranosyl)pyrimido[1,2 alpha]purin-10(3H)-one (MDA-MG-1), formed from the metabolism of 1 mM chloral hydrate, trichloroacetic acid, and trichloroethanol by control B6C3F1 mouse liver microsomes, mouse pyrazole-induced microsomes, male F344/N rat liver microsomes, and human liver microsomes in the presence and absence of calf thymus DNA was also determined. When incubated in the absence of calf thymus DNA, the amount of malondialdehyde formed from metabolism by pyrazole-induced mouse microsomes was twice that from rat or human liver microsomes. Amounts of chloral hydrate-induced and trichloroacetic acid-induced lipid peroxidation products formed from metabolism by rat and human liver microsomes were similar, and these quantities were about twice those formed from the metabolism of trichloroethanol. The quantity of MDA-MG-1 formed from the metabolism of chloral hydrate, trichloroacetic acid, and trichloroethanol by mouse, rat, and human liver microsomes exhibited a linear correlation with the quantity of malondialdehyde formed under incubation conditions in the absence of calf thymus DNA. Chloral hydrate was shown to be mutagenic in vitro and in vivo. At doses from 1,000 to 10,000 micrograms/plate, it induced mutations in S. typhimurium strain TA100, with and without S9 activation; an equivocal response was obtained in S. typhimurium strain TA98 in the absence of S9, and no mutagenicity was detected with strain TA1535 or TA1537. Chloral hydrate at doses from 1,700 to 5,000 micrograms/mL induced sister chromatid exchanges; at doses from 1,000 to 3,000 micrograms/mL, chromosomal aberrations were induced in cultured Chinese hamster ovary cells, with and without S9. Results of a sex-linked recessive lethal test in D. melanogaster were unclear; administration of chloral hydrate by feeding produced an inconclusive increase in recessive lethal mutations, results of the injection experiment were negative. An in vivo mouse bone marrow micronucleus test with chloral hydrate at doses from 125 to 500 mg/kg gave a positive dose trend. In summary, due to the absence of chloral hydrate-induced histopathologic lesions in rats and mice, no-observed-adverse-effect levels (NOAELs) were based on body weights of rats and liver weights of mice. The NOAELs for rats and mice were 200 mg/kg. Chloral hydrate was rapidly metabolized by rats and mice, with trichloroacetic acid occurring as the major metabolite. Peak concentrations of trichloroacetic acid occurred more quickly in mice. Plasma concentrations of chloral hydrate were dose dependent, but metabolic rates were unaffected by dose or sex. Chloral hydrate was mutagenic in vitro and in vivo. Metabolism of chloral hydrate and its metabolites produced free radicals that resulted in lipid peroxidation in liver microsomes of mice, rats, and humans. Induction of cytochrome P(450)2E1 by pyrazole increased the concentrations of lipid peroxidation products; inhibition of cytochrome P(450)2E1 by 2,4-dinitrophenylhydrazine reduced these concentrations. Metabolism of chloral hydrate and its metabolites by mouse, rat, and human liver microsomes formed malondialdehyde, and in the presence of calf thymus DNA formed the DNA adduct MDA-MG-1.

The extent of dichloroacetate formation from trichloroethylene, chloral hydrate, trichloroacetate, and trichloroethanol in B6C3F1 mice.

Conflicting data have been published related to the formation of dichloroacetate (DCA) from trichloroethylene (TRI), chloral hydrate (CH), or trichloroacetic acid (TCA) in B6C3F1 mice. TCA is usually indicated as the primary metabolic precursor to DCA. Model simulations based on the known pharmacokinetics of TCA and DCA predicted blood concentrations of DCA that were 10- to 100-fold lower than previously published reports. Because DCA has also been shown to form as an artifact during sample processing, we reevaluated the source of the reported DCA, i.e., whether it was metabolically derived or formed as an artifact. Male B6C3F1 mice were dosed with TRI, CH, trichloroethanol (TCE), or TCA and metabolic profiles of each were determined. DCA was not detected in any of these samples above the assay LOQ of 1.9 microM of whole blood. In order to slow the clearance of DCA, mice were pretreated for 2 weeks with 2 g/liter of DCA in their drinking water. Even under this pretreatment condition, no DCA was detected from a 100 mg/kg i.v. dose of TCA. Although there is significant uncertainty in the amount of DCA that could be generated from TRI or its metabolites, our experimental data and pharmacokinetic model simulations suggest that DCA is likely formed as a short-lived intermediate metabolite. However, its rapid elimination relative to its formation from TCA prevents the accumulation of measurable amounts of DCA in the blood.

Metabolism of chloral hydrate in mice and rats after single and multiple doses.

Chloral hydrate is a hepatocarcinogen in mice but not rats. To examine this species-related difference, male and female B6C3F1 mice and Fischer (F344) rats were treated by gavage with 1 or 12 doses of chloral hydrate, and concentrations of the drug and its metabolites were determined in plasma at 0.25, 7, 3, 6, and 24 h and 2, 4, 8, and 16 d after the last treatment. Maximum levels of chloral hydrate were observed at the initial sampling time of 0.25 h. By 1 h, levels dropped substantially, and by 3 h, chloral hydrate could not be detected. Trichloroacetic acid was the major metabolite found in the plasma, with peak levels being observed 1-6 h after dosing. The concentrations then slowly decreased such that by 2 d this metabolite could no longer be detected. Trichloroethanol was assayed as both the free alcohol and its glucuronide. Maximum levels of trichoroethanol occurred at 0.25 h, and by 1-3 h approached the limits of detection. A pharmacokinetic model was constructed to describe the metabolic data. The plasma half-life values of chloral hydrate were similar in both species. In mice, the rate of elimination of trichloroacetic acid was significantly increased after multiple doses; this difference was not observed with rats. The half-life of trichloroethanol and its glucuronide was significantly greater in rats as compared to mice. None of the metabolic parameters appears to account for the hepatocarcinogenicity of chloral hydrate seen in mice but not rats.

[The plasma level of the neurotoxin 1-trichloromethyl-1,2,4,5-tetrahydro-beta-carboline (TaClo) in man after oral administration of chloral hydrate]. / Untersuchungen zu Plasmaspiegeln des Neurotoxins 1-Trichlormethyl-1,2,3,4-tetrahydro-beta-carbolin (TaClo) beim Menschen nach oraler Verabreichung von Chloralhydrat.

Chloral hydrate (CAS 302-17-0) is a widely used hypnotic and sedative agent. It was recently reported in the literature that a neurotoxin, TaClo (1-trichloromethyl-1,2,3,4-tetrahydro-beta-carboline), may be formed in vitro from tryptamine (Ta) and chloral (Clo). Intraperitoneal administration of TaClo led to parkinson-like symptoms in the rat. Hence, the plasma levels of TaClo were determined at various time-points in 18 healthy volunteers in two periods each during a bioavailability study of several chloral hydrate preparations. The limit of quantitation for TaClo was 5 ng/ml. No TaClo could be determined in the plasma of the various volunteers following administration of human therapeutic doses of chloral hydrate. Hence, it is unlikely that TaClo will be formed in man after application of therapeutic doses of chloral hydrate to patients.

[The relative bioavailability and pharmacokinetics of chloral hydrate and its metabolites]. / Untersuchungen zur relativen Bioverfügbarkeit und Pharmakokinetik von Chloralhydrat und seinen Metaboliten.

Two open, randomized cross-over trials were performed in 18 healthy volunteers each to evaluate the relative bioavailability and the pharmacokinetics of chloral hydrate (CAS 302-17-0), the active ingredient of Chloraldurat 500 (immediate release capsules, CH), Chloraldurat rot (immediate release capsules, CR) and Chloraldurat blau (enteric-coated modified release capsules, CB). In the first study the male subjects, aged 21 to 31 years, were randomly given one capsule of CH or 500 mg of chloral hydrate as drinking solution. In the second study the volunteers, aged 20 to 28 years, received either one capsule of CR or one capsule of CB or 250 mg of chloral hydrate as drinking solution. The time of administration was between 6:30 and 7:30 a.m. and the capsules had to be swallowed with 150 ml water. The reference medication consisted of 150 ml drinking solution. The wash out time in both studies was 4 weeks. Prior to the administration and (2, 4, 6, only for CH) 8, 10, 15, 20, 40, 60 min and 1.5, 2, 4, 6, 8, 12, 24, 36, 48, 72, 96, 144, 192, 240 (and 408 only for CR/CB) h afterwards blood samples of 4.5 ml were taken from the antecubital vein. Additional 4.5 ml were drawn before and 10, 20, 40 and 60 min after administration to detect unchanged chloral hydrate. In the second study times of blood sampling were modified up to 4 h after administration due to the estimated later onset of release from CB in comparison to CR. Blood samples were centrifuged within 20 min, the plasma was separated and immediately frozen at -20 degrees C. Due to the extremely short terminal half-life of chloral hydrate its active metabolite trichloroethanol is regarded as the pharmacokinetically relevant parameter for the assessment of the bioavailability of the parent substance. Compared to the reference formulation (drinking solution) the bioavailability of trichloroethanol was 94.8% (CH), 100.7% (CR) and 101.6 (CB), respectively. The maximum plasma concentrations (Cmax) of trichloroethanol were 5176 ng/ml after intake of CH (reference 6131 ng/ml), after intake of CR 3241 ng/ml and CB 3279 ng/ml (reference 2993 ng/ml). Maximum plasma concentrations (tmax) of trichloroethanol were reached after 0.67 h (reference) and after 0.98 (CH), 0.76 (CR) and 2.38 h (CB), respectively. The terminal half-life for trichloroethanol was calculated to be 9.3 to 10.2 h, for the inactive metabolite trichloracetic acid the half-life ranged from 89 to 94 h. Chloral hydrate itself could be detected only 8 to 60 min after application at very low concentrations in some of the plasma samples. It is justified to characterize its bioavailability by the active metabolite trichloroethanol due to the extremely short terminal half-life and high variability of the parent substance.

A physiologically based pharmacokinetic model for trichloroethylene and its metabolites, chloral hydrate, trichloroacetate, dichloroacetate, trichloroethanol, and trichloroethanol glucuronide in B6C3F1 mice.

A six-compartment physiologically based pharmacokinetic (PBPK) model for the B6C3F1 mouse was developed for trichloroethylene (TCE) and was linked with five metabolite submodels consisting of four compartments each. The PBPK model for TCE and the metabolite submodels described oral uptake and metabolism of TCE to chloral hydrate (CH). CH was further metabolized to trichloroethanol (TCOH) and trichloroacetic acid (TCA). TCA was excreted in urine and, to a lesser degree, metabolized to dichloroacetic acid (DCA). DCA was further metabolized. The majority of TCOH was glucuronidated (TCOG) and excreted in the urine and feces. TCOH was also excreted in urine or converted back to CH. Partition coefficient (PC) values for TCE were determined by vial equilibrium, and PC values for nonvolatile metabolites were determined by centrifugation. The largest PC values for TCE were the fat/blood (36.4) and the blood/air (15.9) values. Tissue/blood PC values for the water-soluble metabolites were low, with all PC values under 2.0. Mice were given bolus oral doses of 300, 600, 1200, and 2000 mg/kg TCE dissolved in corn oil. At various time points, mice were sacrificed, and blood, liver, lung, fat, and urine were collected and assayed for TCE and metabolites. The 1200 mg/kg dose group was used to calibrate the PBPK model for TCE and its metabolites. Urinary excretion rate constant values were 0. 06/hr/kg for CH, 1.14/hr/kg for TCOH, 32.8/hr/kg for TCOG, and 1. 55/hr/kg for TCA. A fecal excretion rate constant value for TCOG was 4.61/hr/kg. For oral bolus dosing of TCE with 300, 600, and 2000 mg/kg, model predictions of TCE and several metabolites were in general agreement with observations. This PBPK model for TCE and metabolites is the most comprehensive PBPK model constructed for P450-mediated metabolism of TCE in the B6C3F1 mouse.

Kinetics and metabolism of chloral hydrate in children: identification of dichloroacetate as a metabolite.

Chloral hydrate was introduced into therapeutics more than 100 years ago, and since then a number of kinetic and metabolic studies have been conducted on this drug. Trichloroethanol, its glucuronide and trichloroacetic acid have been identified as the metabolites of chloral hydrate. We now report the identification of dichloroacetate as a major product of chloral hydrate metabolism in children, in addition to trichloroethanol and trichloroacetic acid. Furthermore, pretreatment of children with chloral hydrate appears to retard the plasma clearance of dichloroacetate.

[The metabolism and bactericidal properties of the blood neutrophilic granulocytes in experimental typhoid intoxication]. / Metabolizm i bakteritsidnye svoistva neitrofil'nykh granulotsitov krovi pri éksperimental'noi briushnotifoznoi intoksikatsii.

The levels of succinate dehydrogenase (SDG), lactate dehydrogenase (LDG), glucose-6-phosphate-dehydrogenase (G-6-PDG), myeloperoxydase (MPO), glycogen and cationic proteins were determined in the neutrophilic granulocytes of peripheral blood of 79 rabbits after experimental contamination by endotoxin of S. typhi. The bactericidal system of neutrophils was stimulated due to the depression of SDG, activation of LDG and G-6-PDG levels. Administration of indometacinum and chlotasolum blockaded the cyclooxygenase fermentative system of prostaglandin synthesis and thus decreased the activity of S. typhi endotoxin.