[Human toxicokinetic of hexobarbital after acute multi-drug intoxication]. / Etude de la toxicocinétique de l'hexobarbital après intoxication aiguë polymédicamenteuse.

A 33-year-old man was hospitalized unconscious on suspicion of acute diazepam and hexobarbital intoxication, a barbiturate not marketed in France. Its quantification was developed by gas chromatography coupled with mass spectrometry detection and validated on one-hundred microL of plasma extracted by a liquid/liquid method. Hexobarbital and diazepam concentrations in initial plasma samples were at toxic levels, respectively 15 900 ng/mL and 13 800 ng/mL. Hexobarbital toxicokinetic was studied during 175 h and analysed with a non-compartmental model. Half-life value of 61,8 h was found, being much longer than already published hexobarbital half-lives (between 3.2 h and 6.9 h). The reasons of this long half-life were discussed according to metabolism and pharmacogenetic.

Physical dependence after benzodiazepine treatments in rats: Comparison of short and long treatments with diazepam and lorazepam.

OBJECTIVE: This study examined the development of physical dependence after different durations of treatments with two benzodiazepines (diazepam and lorazepam). METHOD: Increased excitation in the central nervous system during a 2-week withdrawal period after 4-day and 4-week treatments with diazepam and lorazepam was examined with an EEG threshold method in male rats. Increased excitation was measured as a decreased sensitivity to hexobarbital (i.e., increased threshold doses). The concentrations of hexobarbital in two different brain regions, serum, fat and muscle tissue after 4-week treatment with diazepam were determined with a high-pressure liquid chromatography method. RESULTS: The duration of withdrawal was influenced by the duration of treatment but the maximum level of withdrawal excitation was similar for both drugs. Equieffective doses of diazepam (20 mg/kg) and lorazepam (2 mg/kg) induced similar patterns of withdrawal excitability after both treatments. The brain concentrations of hexobarbital were significantly higher on Days 1 and 3 of withdrawal after diazepam treatment. Significant correlations between the threshold doses and brain concentrations were found on Day 1, but these correlations disappeared on day 3. At the same time, a difference between the concentrations of hexobarbital in different brain areas emerged. CONCLUSIONS: The duration of treatment had a minor influence on the pattern of withdrawal excitation. Equieffective doses of diazepam and lorazepam induced comparable withdrawal excitability indicating no significant difference in their potential to induce physical dependence. The time-dependent change in the hexobarbital concentrations in the brain suggests that withdrawal excitation after diazepam treatment is a complex phenomenon probably involving several different systems at different times.

A study of the duration of acute tolerance induced with hexobarbital in male rats.

Male rats were infused i.v. with hexobarbital to obtain a burst suppression of 1 s or more in the EEG (SS). At SS the rats were killed and the concentration of hexobarbital was determined by HPLC in three parts of the brain. Acute tolerance (induced by a 1-h exposure at the SS level) was recorded as an approximately 20% increase in brain concentrations of hexobarbital at the last SS during the exposure when compared with concentrations recorded at the first SS in the controls. Increased brain concentrations (approximately 8%) at SS were recorded 24 h after induction of acute tolerance. After 48 h the increase was uncertain. Thus, acute tolerance to hexobarbital could have cumulative properties if new exposures are imposed after 24 h.

Phase I and phase II xenobiotic biotransformation in different inbred strains of rats: study in immobilized perfused hepatocytes.

The present study was designed to compare phase I and phase II biotransformation reactions in immobilized perfused hepatocytes as a cellular system obtained from inbred rat strains which represent models for some cardiovascular diseases, namely, spontaneously hypertensive rats (SHR), rats sensitive and resistant to isoprenaline-induced myocardial lesions (IS and IR, respectively) as compared to Wistar rats (W). The biotransformation kinetics for hexobarbital (HX), 7-ethoxycoumarin (7-EC), 1-chloro-2,4-dinitrobenzene (CDNB) and 4-nitrophenol (4-NP) were followed up in the hepatocyte perfusate. W and SHR rat hepatocytes have metabolized HX at a higher rate than those of the IR and IS strains. Hepatocytes from the W strain exhibited a higher rate of 7-EC deethylation activity compared to hepatocytes obtained from the IR or IS strains. Hepatocytes obtained from SHR and IR rats showed the highest glutathione-S-transferase (GST) activity towards CDNB compared to the IS or W strain. 4-NP disappearance was higher in the perfusion medium of hepatocytes obtained from the W and IS strains compared to the IR strain. These significant differences in drug biotransformation between various studied strains, which may be genetically determined, can be well demonstrated by using an efficient drug metabolizing model of the immobilized perfused hepatocytes. The importance of these differences should be considered during the study of the experimental therapy of the relevant disease as obtained from the specific experimental strain, where it may be expected that the pharmacokinetic profile of a drug in vivo and consequently its pharmacodynamic or toxic effects will be strain dependent.

Endotoxin depresses hepatic cytochrome P450-mediated drug metabolism in women.

AIMS: In men, the inflammatory response to intravenous endotoxin depresses apparent oral clearances of antipyrine, hexobarbitone, and theophylline. The aim of this study was to investigate whether there might be gender differences in the regulation of hepatic cytochromes P450. METHODS: Experiments were carried out in seven healthy women volunteers (ages 19-51, median 22 years). Each woman received a cocktail of the three drugs on two occasions, once after a saline injection and again after endotoxin. RESULTS: Endotoxin injections, but not saline, caused the expected physiologic responses of inflammation including fever and increases in circulating tumor necrosis factor-alpha, interleukin-6, and C-reactive protein. When compared with the saline control studies, endotoxin significantly decreased clearances of all probes: antipyrine, 31% (95%CI 21%-41%); hexobarbitone, 20% (95%CI 10-31%); and theophylline, 20% (95%CI 10%-30%). The decreases were comparable with those found in the men previously studied (35%, 27%, and 22%, respectively). CONCLUSIONS: These data show that endotoxin-induced inflammation decreases hepatic cytochrome P450-mediated metabolism of selected probe drugs in women as it does in men.

The upregulating effect of dexamethasone on tumor necrosis factor production is mediated by a nitric oxide-producing cytochrome P450.

Dexamethasone (DEX) is a well-known inhibitor of tumor necrosis factor (TNF) production when given shortly before lipopolysaccharide (LPS). However, DEX (10 mg/kg, ip) potentiates TNF production when administered 24-48 hr before LPS (16 micrograms/kg, ip). We have found that this is probably due to DEX induction of cytochrome P450 3A, which is known to produce nitric oxide (NO). The upregulating effect of DEX on TNF production is associated with increased NO production. Both the upregulation of NO and of TNF production by DEX are inhibited by co-administration of the P450 3A inhibitor troleandomycin (TAO, 40 mg/kg, ip). These data suggest that P450 3A-generated NO might be involved in TNF induction.

Endotoxin administration to humans inhibits hepatic cytochrome P450-mediated drug metabolism.

In experimental animals, injection of gram-negative endotoxin (LPS) decreases hepatic cytochrome P450-mediated drug metabolism. To evaluate this phenomenon in a human model of gram-negative sepsis, LPS was administered on two consecutive days to healthy male volunteers during which time a cocktail of antipyrine (AP-250 mg), hexobarbital (HB-500 mg), and theophylline (TH-150 mg) was ingested and the apparent oral clearance of each drug determined. Each subject had a control drug clearance study with saline injections. In the first experiment, six subjects received the drug cocktail 0.5 h after the first dose of LPS. In the second experiment, another six subjects received the drug cocktail 0.5 h after the second dose of LPS. In both experiments, LPS caused the expected physiologic responses of inflammation including fever with increases in serum concentrations of TNF alpha, IL-1 beta, IL-6, and acute phase reactants. In the first experiment, only minor decreases in clearances of the probe drugs were observed (7-12%). However in the second experiment, marked decreases in the clearances of AP (35, 95% CI 18-48%), HB (27, 95% CI 14-34%), and TH (22, 95% CI 12-32%) were seen. The decreases in AP clearance correlated with initial peak values of TNF alpha (r = 0.82) and IL-6 (r = 0.86). These data show that in humans the inflammatory response to even a very low dose of LPS significantly decreases hepatic cytochrome P450-mediated drug metabolism and this effect evolves over a 24-h period. It is likely that septic patients with much higher exposures to LPS have more profound inhibition of drug metabolism.

Metabolic actions of a single atenolol and metoprolol dose.

Atenolol (CAS 29122-68-7) and metoprolol (CAS 37350-58-6) are beta 1-selective adrenoceptor antagonists without intrinsic sympathomimetic activity. beta-Receptor blockers influence carbohydrate- and lipid metabolism. Liver is a central organ of these processes. The metabolic fate of a single oral atenolol and metoprolol dose and their actions on carbohydrate- and lipid parameters have been investigated. Healthy male rats received a dose reducing heart beat/min by 25% (atenolol: 6 mg/kg; metoprolol: 10 mg/kg). About 9% of atenolol is metabolized by cytochrome P-450 (P-450). P-450-dependent functions (aminopyrine-N-demethylase, hexobarbital biotransformation time) were not inhibited. Serum bilirubin was normal. Triglyceride (TG), total cholesterol and HDL-cholesterol levels of the plasma were not affected. Transient blood glucose increase was measured returning to initial value at 120 min. Metoprolol is metabolized by hepatic monooxygenases. P-450-dependent functions were inhibited correlating to the lowered P-450-content of the microsomes. High TG level and decreased HDL-cholesterol content were measured. Blood glucose was significantly high. The liposoluble metroprolol affected the hepatic functions more than the hydrophilic atenolol. The monitoring of blood glucose during beta-receptor antagonist treatment may be suggested.

Effects of furazolidone on duration of righting reflex loss induced with hexobarbital and zoxazolamine in the rat.

Effects of furazolidone (FZ) on the sleeping time induced with hexobarbital (HEX) and paralysis time induced by zoxazolamine (ZOX) were investigated by measuring the length of time required to recover from righting reflex loss in rats after oral administration of FZ at doses of 50, 100, 200 and 400 mg/kg/day for 4 successive days. Administration of 50 mg/kg to rats of both sexes induced no effect on the HEX sleeping time, but of 100 mg/kg FZ or more induced prolongation of sleeping time dose-dependently. In female rats, HEX sleeping time of the control group was twice that of the male rats, but HEX sleeping time after receiving FZ above 200 mg/kg was approximately the same as in the male rats. ZOX paralysis time exhibited no sex differences in the control rats, and it was significantly prolonged by FZ at a dose of 100 mg/kg or more. No significant differences in blood levels of HEX and ZOX at the time of recovery were found between the control and FZ treated rats, suggesting that FZ produced prolongation of the drug effects was due to the maintenance of the blood levels rather than the change in the sensitivities of rats at the receptor sites. Body weight gains were inhibited in the rats treated with FZ at doses over 100 mg/kg. Cytochrome P-450 content in hepatic microsomes in the rats which received 100 mg/kg FZ were slightly increased. It is suggested that successive oral administration of FZ to rats at high doses impaired drug clearance and this resulted in the prolongation of HEX sleeping and ZOX paralysis times.

[The characteristics of the effect of centimeter-range microwaves on drug pharmacokinetics in the body of experimental animals]. / Osobennosti vliianiia mikrovoln santimetrovogo diapazona na farmakokinetiku medikamentov v organizme éksperimental'nykh zhivotnykh.

The experiments on 130 rat males have shown that the exposure of the animals' liver to centimeter microwaves enhances catalytic activity of P-450p cytochrome, an enzyme of drug microsomal metabolism. However, changes in pharmacokinetic parameters of elimination from the blood of the drugs based on microsomal substrates of hepatic enzymatic system are more dependent on the microwaves' impact on physiological factors modifying drug pharmacokinetics. This implies the necessity of pharmacokinetic investigations in each individual case of combining drugs with microwaves.

The influence of aging on the metabolism of simultaneously administered hexobarbital enantiomers and antipyrine before and after phenobarbital induction in male rats: a longitudinal study.

The influence of aging on the metabolism of antipyrine (AP) and hexobarbital enantiomers (R-HB and S-HB) with and without phenobarbital (PB) induction was investigated in a longitudinal study in rats aged 6, 12, 24 and 30 months. The metabolic clearances of AP (Clm AP), R-HB (Clm R-HB) and S-HB (Clm S-HB) were used as indicators for P450 enzyme activities in vivo. This also included the assessment of the clearances of formation of three AP metabolites, 3-hydroxymethylantipyrine (Cl-->HMA), 4-hydroxyantipyrine (Cl-->OHA) and norantipyrine (Cl-->NORA). Aging appeared to have little influence on the pharmacokinetics of the model compounds. By contrast, the influence of PB pretreatment on Clm AP changed dramatically with aging. The extent of induction decreased from 4.5-fold at 6 months to 1.7-fold at 30 months. Aging influenced the clearances of formation of the three metabolites differentially. Clm S-HB was about six times higher than Clm R-HB without induction. After PB induction, S-HB did not reach detectable levels in plasma at 6, 12 and 24 months. At 30 months, PB pretreatment resulted in a significantly decreased Clm S-HB when compared with the uninduced state. The extent of induction of R-HB metabolism had decreased strongly at 24 and 30 months. The present results clearly indicate that in the aged rat, the P450 enzyme system is much less sensitive to PB induction.

Stereoselective disposition of hexobarbital and its metabolites: relationship to the S-mephenytoin polymorphism in Caucasian and Chinese subjects.

In vitro studies with human liver preparations suggest that the metabolism of hexobarbital involves CYP2CMP--the determinant of the S-mephenytoin 4'-hydroxylation polymorphism, but no in vivo evidence of interphenotypic differences exist. The pharmacokinetics and urinary excretion of hexobarbital and its metabolites were, therefore, investigated following oral administration of a differentially labelled pseudoracemate that allowed determination of the fate of the individual enantiomers. Studies were undertaken in 10 Caucasian and nine Chinese healthy subjects known to be either extensive (EM) or poor (PM), metabolizers of mephenytoin. No inter-racial differences were observed in any of the measured parameters within a given phenotype. However, pronounced stereoselectivity in disposition was noted in EMs with R-(-)-hexobarbital's oral clearance being five- to six-fold greater than that for the S-(+)-enantiomer. By contrast, the S-(+)-isomer was eliminated twice as fast as R-(-) hexobarbital in PMs and, in addition, the oral clearances of both enantiomers were significantly reduced compared with their values in EMs. Formation of 3'-hydroxy- and 3'-ketohexobarbital and 1,5-dimethylbarbituric acid were the major identified routes of metabolism for each enantiomer in both phenotypes. Furthermore, these pathways were found to co-segregate with the mephenytoin polymorphism and in EMs they were primarily responsible for the observed stereoselectivity in disposition. These findings, therefore, confirm the stereoselectivity in hexobarbital's disposition in humans and identify the major pathways of metabolism involved. Additionally, the results indicate that CYP2CMP is a major determinant of the in vivo metabolism of both of hexobarbital's enantiomers but especially that of the R-(-)-enantiomer.

Effects of interferon-alpha monotherapy on hepatic drug metabolism in cancer patients.

1. The influence of interferon-alpha (IFN alpha) on the clearances of theophylline (TH), antipyrine (AP) and hexobarbitone (HB) was studied in seven cancer patients given IFN alpha as their only treatment. In addition, IFN alpha effects on drug clearance were correlated with changes in serum inflammatory cytokines and acute phase proteins. 2. A 'baseline' study was performed by administering an oral drug 'cocktail' of TH (150 mg), AP (250 mg) and HB (250 mg) with saline injected simultaneously and again 24 h later. One week later, an 'acute' study was performed at the initiation of IFN alpha therapy, 3 x 10(6) units injected with the drug cocktail and again 24 h later. After 2 weeks of IFN alpha treatment three times per week, a 'chronic' study was performed with IFN alpha injected the day prior to, simultaneously with, as well as 24 h after the drug cocktail. 3. Plasma samples were collected over 48 h and the clearances of TH, AP and HB were estimated. Serum samples were collected at various times for the measurement of tumor necrosis factor (TNF), interleukin-1 (IL-1), interleukin-6 (IL-6), C-reactive protein (C-RP) and alpha 1-acid glycoprotein (AGP). 4. IFN alpha caused a 33% decrease in the oral clearance of TH during the chronic study compared with baseline (P < or = 0.05). Although IFN alpha inhibited TH clearance by 16% during the acute study and AP clearance by 20-21% during both acute and chronic studies, these changes did not reach statistical significance. IFN alpha caused minimal changes in HB clearance. There were no chronic effects of IFN alpha on serum cytokines or acute phase proteins. 5. The findings confirm that the most commonly used dose of IFN alpha inhibits the hepatic clearance in humans of some but not all drugs and that this inhibition persists during IFN alpha therapy. Because inhibition was not associated with increases in serum cytokines or acute phase proteins, the mechanism by which IFN alpha inhibits cytochrome P450 activities in vivo does not appear to involve inflammatory mediators such as TNF. IL-1 or IL-6.

[The effect of phytin, benzonal and their combination administered prophylactically on the pharmacodynamics of drugs metabolized in the liver in hypokinesia]. / Vliianie fitina, benzonala i ikh kombinatsii pri profilakticheskom vvedenii na farmakodinamiku lekarstvennykh veshchestv, metaboliziruiushchikhsia v pecheni pri gipokinezii.

Hexenal, meprobamate, amidopyrine and ethylmorphine produced a significantly marked effect in animals under hypokinesia as compared with normal rats. When phytin, benzonal and their combination were used for preventive purposes, impaired pharmacodynamics of the tested drugs metabolizing in the liver disappeared. The investigations demonstrated that the preventive use of phytin in combination with benzonal is the most optimal in correcting the impairments of drug pharmacodynamics in hypokinesia.

Influence of age on stereoselective pharmacokinetics and metabolism of hexobarbital in the rat.

The influence of age on stereoselective pharmacokinetics and in vitro metabolism of R- and S-hexobarbital was studied in the rat. After intravenous administration of the racemate, the plasma concentrations of S-hexobarbital are markedly lower than those of R-hexobarbital. For S-hexobarbital the half-life is somewhat shorter and the volume of distribution and plasma clearance is higher than for its antipode. For both enantiomers an increase in AUC and half-life, and a decrease in clearance are observed with aging. These changes occur mainly between the 3rd and the 12th month and are slightly more pronounced for R- than for S-hexobarbital, as appears from the S/R ratios. The volume of distribution shows no changes with aging. In vitro disappearance rate in 3-month-old rats is significantly higher for S- than for R-hexobarbital. There is for both enantiomers an increase in disappearance rate in 12-month-old rats as compared to younger or older rats, but this is significant only for the R-enantiomer. There are pronounced differences in the kinetics and metabolism of both hexobarbital enantiomers; changes with aging occur, but are only slightly and not always significantly more important for R- than for S-hexobarbital.

Effects of phenolic smoke condensates and their components on hepatic drug metabolizing systems.

Treatment of food with wood smoke is a long-established method of preservation and flavouring food. Recently, hardwood smoke condensates, purified of polycyclic hydrocarbons, have become of importance for direct flavouring of sausage-meat. The acute toxicity of the purified phenolic fraction in mice after intraperitoneal administration was therefore investigated. The LD50 was found to be 940 mg/kg body weight, which is about three times the LD50 of phenol (about 300 mg/kg). Only high concentrations of phenols or smoke condensate fractions are able to damage cytochrome P-450 by conversion to cytochrome P-420, whereas lower concentrations exhibit inhibitory effects on monooxygenase activity. Inductive properties of the phenolic fractions could not be demonstrated. Concentrations in vivo of free phenolic compounds do not reach inhibitory levels, since the hexobarbital-induced sleeping-time and 14CO2-exhalation after administration of p-[methoxy-14C] acetanilide are not altered. It is concluded that the phenolic compound intake with food regularly treated with smoke condensate fractions is below a toxicologically relevant level.

Inhibition of hepatic drug biotransformation by carrageenan-induced inflammation in the rat: effect of sex hormone alterations.

Following in vivo treatment with carrageenan, sex-related differences in alteration of hepatic drug metabolism were found in the rat. In adult male rats, marked decreases were observed in hepatic 9000 x g supernatant cytochrome P-450 content and in the biotransformation of hexobarbital, aminopyrine, ethylmorphine, and meperidine. Hexobarbital hypnosis was significantly prolonged by carrageenan treatment in intact and testectomized animals as compared to their respective controls. Although carrageenan-treated intact animals slept 480% longer, carrageenan-treated testectomized rats slept only 60% longer than the respective control animals. However, testectomy or administration of 17 beta-estradiol to testectomized male rats did not inhibit the monooxygenase activities by carrageenan-treatment. Furthermore, administration of testosterone to ovariectomized female rats did not antagonize the inhibitory effects of the carrageenan-induced inflammation. The inhibitory effects produced by carrageenan-induced inflammation on the microsomal enzyme system were observed only in mature male rats and were not observed in mature female rats or in sexually immature rats of either sex. Thus, these results suggest that the inhibitory effects of carrageenan-induced inflammation on hepatic 9000 x g supernatant monooxygenases in the male rat are partially mediated through the toxic action of carrageenan-induced inflammation on androgen-dependent factors in this enzyme system.

[Drug clearance as a decision aid for further invasive liver diagnosis--studies with hexobarbital as a model substrate]. / Die Arzneimittelclearance als Entscheidungshilfe für eine weiterführende invasive Leberdiagnostik--Untersuchungen mit Hexobarbital als Modellsubstrat.

The clearance of a drug predominantly metabolized in the liver may serve as an estimate of quantitative liver function. In 260 consecutive patients presenting with a history of liver disease and abnormal laboratory findings but without a current definite diagnosis we have measured the clearance of hexobarbital and investigated if low values in patients are able to support the decision for an invasive diagnostic procedure such as needle biopsy or laparoscopy. 250 mg of hexobarbital was given orally to the patients between 8 and 10 hrs p.m. 12 hrs later blood samples were taken. Hexobarbital was determined by gas chromatography with N-selective detection, and a single point clearance was calculated. We recommended liver biopsy or laparoscopy to all patients with a hexobarbital clearance below 2.7 ml/min/kg body weight (normal 2.66-5.34 ml/min/kg). 73 out of 260 patients showed a reduced hexobarbital clearance. In 44 patients blind liver biopsy (n = 14) or laparoscopy (n = 30) was performed, 29 patients refused an invasive diagnostic procedure. 17 out of 26 patients with the tentative diagnosis chronic hepatitis had already an incomplete or complete liver cirrhosis. In 11 out of 18 patients with the tentative diagnosis alcohol toxic liver injury we found a progressive portal fibrosis or complete liver cirrhosis. Reduced drug clearance reflecting quantitative liver function can be an indicator of advanced liver disease, thus adding substantially to the decision for further invasive diagnostic procedures.

[Applications of positron emission tomography (PET) to the measurement of regional cerebral pharmacokinetics]. / Anwendungen der Positronen-Emissions-Tomographie (PET) zur Messung regionaler zerebraler Pharmakokinetiken.

Positron emission tomography (PET) has not only a variety of applications to functional diagnostics using methods of nuclear medicine and for the investigation of pathophysiological processes, it also offers new possibilities for pharmacology. As PET is able to quantitatively record "from outside" the regional concentration of a positron emitter in a living primate, the distribution and kinetics of a labelled drug at the site of action can be determined non-invasively. This is always the case if the research substance can be labelled practically carrier-free with a short-lived positron emitter such as 11C (T1/2 = 20 min) or if applicable 18F (T1/2 = 110 min). The quantities applied in this case are so small that pharmacodynamic effects do not occur. Therefore, this method is particularly suitable for measuring in vivo the regional cerebral pharmacokinetics of centrally acting drugs in humans.