[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.

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.

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.

Age-associated stereoselective alterations in hexobarbital metabolism.

This clinical investigation was designed to study the influence of age on stereoselective drug disposition using hexobarbital as a model marker. The disposition of hexobarbital enantiomers was investigated in 10 young and 10 elderly, healthy male volunteers. Mean oral clearance (+/- SD) of d-hexobarbital (1.9 +/- 0.5 vs. 1.7 +/- 0.3 ml/min/kg; P greater than 0.05) did not differ significantly between the young and elderly subjects, respectively. However, despite wide intersubject variability, l-hexobarbital mean oral clearance (+/- SD) was approximately twofold greater in the young than in the elderly subjects (16.9 +/- 11.9 vs. 8.2 +/- 3.2 ml/min/kg; P less than 0.05). This resulted in a significantly greater enantiomeric oral clearance ratio in the young when compared with the elderly subjects (8.3 +/- 3.4 vs. 4.7 +/- 1.4; P less than 0.01). No significant difference (P greater than 0.05) in pharmacologic response after hexobarbital administration was found between the two groups. Demonstration of an age-related preferential decline in metabolism of one enantiomer over another has not been reported previously for any racemic drug in animals or humans.

Pharmacokinetics of hexobarbital in young and old rats.

Hexobarbital is a drug widely used to study the capacity of the liver to metabolize drugs. The pharmacokinetics of hexobarbital in 3- and 30-month-old male BN/BiRij rats were studied. The half-life of hexobarbital in 30-month-old rats (39.9 +/- 4.1 min) was significantly higher than that of 3-month-old ones (21.3 +/- 3.8 min). The volume of distribution (ml.kg-1 body weight) did not change with age. The intrinsic clearance, expressed as ml.min-1.kg-1 body weight, of hexobarbital in 30-month-old rats (20.2 +/- 6.6) was half that of the 3-month-old ones (39.5 +/- 7.6). Further studies will be performed to investigate the effect of age on the intrinsic clearance of S(+)- and R(-)- hexobarbital.

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.

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.

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.

Disposition of hexobarbitone and antipyrine in DOCA-hypertensive rats.

The disposition of antipyrine and hexobarbitone, and their effects on drug metabolizing hepatic enzymes have been investigated in DOCA-hypertensive rats. Antipyrine pharmacokinetic parameters were the same in hypertensive and control animals. Hexobarbitone sleeping time was longer in hypertensive rats compared with controls, while the activity of hepatic hexobarbitone hydroxylase was the same in both groups. Hepatic aminopyrine-N-demethylase activity was elevated in hypertensive rats while aniline hydroxylase and aryl hydrocarbon hydroxylase were lower. Glucuronyl transferase was the same in both groups. The sensitivity of the central nervous system of hypertensive rats to hexobarbitone was not altered, as determined by hexobarbitone concentration in blood and in brain. The total hepatic blood flow (arterial and portal) was significantly increased. Thus it is suggested that the difference in the disposition of the two drugs is probably not due to drug metabolizing enzyme activity. It is likely that the increase in total hepatic blood flow and rapid saturation of hepatic hexobarbitone metabolizing enzymes have significant roles in the slower metabolism and increased activity of hexobarbitone in hypertensive rats as compared with control rats.

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.

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.

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 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.

[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.

Acute tolerance to and distribution of hexobarbital in relation to depth and duration of anaesthesia in rats.

The development of acute tolerance to hexobarbital was investigated with an EEG-threshold method in rats. Hexobarbital was infused in a tail vein and the effect was monitored either by continuous EEG-recording (using the criterion "silent second") or by continuous observation. Anaesthesia was maintained at the level of "the silent second" for periods of up to 120 min. After different time intervals the last infusion period to the EEG-criterion was followed by decapitation and samples from blood, brain, muscle and fat were analysed for hexobarbital content. Brain concentrations at the EEG criterion increased and were notable after 10 min. but statistically significant at 30 min. when a 40% increase in concentration was needed to reach the criterion. Another group of rats kept at a lower level of anaesthesia (i.e. the righting reflex) showed a slight but not always significant increase in concentration when measured in different parts of the brain at "silent second". The dose of hexobarbital needed to maintain anaesthesia for intervals up to 120 min. increased almost linearly with time. Analysis of serum, muscle and fat tissue showed that concentration in fat tissue increased linearly during this whole interval and served as the final depot in redistribution. Muscle tissue shows an increase up to 60 min. but a very small increase thereafter, which is consistent with a function as temporary storage compartment.

Influence of the rate of hepatic portal vein infusion on hexobarbital pharmacokinetics in the rat.

Pharmacokinetic parameters of hexobarbital were estimated in rats after hepatic portal infusion of a 10-mg dose. Infusion during 10 min resulted in an area under the blood concentration-time curve (AUC) of 556 +/- 83 micrograms.min/ml and a clearance of 83 +/- 13 ml/min.kg, whereas infusion of the same dose during 40 min resulted in values of 272 +/- 36 micrograms.min/ml and 169 +/- 30 ml/min.kg, respectively (mean values +/- SD, n = 3). Infusion during 15 and 20 min provided intermediate values. The decrease of the AUC and the increase of the blood clearance of hexobarbital following decreasing infusion rates clearly indicate nonlinear pharmacokinetics related to the hepatic inflow concentration of hexobarbital.

Age-dependent stereoselective increase in the oral clearance of hexobarbitone isomers caused by rifampicin.

1. The disposition of hexobarbitone enantiomers before and after rifampicin treatment (600 mg daily for 14 days) was investigated in six young (29 +/- 3 years old) and six elderly (71 +/- 4 years old) healthy male volunteers. Hexobarbitone was given as a single 500 mg oral dose of the racemate. 2. The mean (+/- s.d.) oral clearance of S-(+) hexobarbitone was 1.9 +/- 0.3 and 1.8 +/- 0.2 ml min-1 kg-1, respectively, in young and elderly subjects and increased approximately six fold following 14 days of rifampicin treatment in both young (to 11.9 +/- 2.2 ml min-1 kg-1) and elderly (to 10.7 +/- 2.8 ml min-1 kg-1) subjects. 3. In contrast, rifampicin treatment produced a larger and a differential increase in the oral clearance of R-(-) hexobarbitone in young and elderly subjects; an 89 fold change in the young (15.6 +/- 16.4 to 1146.7 +/- 1478.0 ml min-1 kg-1) and a 19 fold change (10.3 +/- 3.0 to 199.9 +/- 98.1 ml min-1 kg-1) in the elderly.

Comparison of anaesthetic and kinetic properties of thiobutabarbital, butabarbital and hexobarbital after intravenous threshold doses in the male rat.

Due to the exceptionally long duration of action of thiobutbarbital the anaesthetic properties of this barbiturate was reinvestigated with an intravenous threshold technique using butabarbital and hexobarbital as references. Adult male rats were used. The criterion of anaesthesia was a burst suppression in the EEG of 1 sec. or more (the "silent second" = SS). The dose which induced the criterion was used as a threshold. The barbiturates were infused with different rates to obtain dose rate curves. After induction of the threshold criterion the animals were either killed and different tissue concentrations were analyzed with a HPLC method or allowed to survive and duration of SS and duration of loss of righting reflex were recorded. With hexobarbital, duration of SS and of loss of righting reflex increased significantly with increasing dose rate. With increasing rates of thiobutabarbital and butabarbital there was in both cases a stepwise increase in duration of SS. At sacrifice, after induction of SS with slow rates brain concentrations of both thiobutabarbital and butabarbital were lower than values recorded after higher rates. The change between the two concentrations was abrupt and occurred at a rate of 20 mg/kg/min. with thiobutabarbital and at the rate of 1.25 mg/kg/min. with butabarbital. This phenomenon was the reverse of acute tolerance which was recorded with hexobarbital and can thus be denoted acute supersensitivity. A kinetic analysis of serum, muscle and fat indicated considerable differences between the barbiturates. As indicated by mortality figures the induction of acute supersensitivity could be potentially dangerous.

[Pharmacokinetic characteristics of drugs in experimental splenectomy]. / Osobennosti farmakokinetiki nekotorykh lekarstvennykh veshchestv pri éksperimental'noi splenéktomii.

Pharmacokinetics of antipyrine, hexenal, phenylbutasone and caffeine was studied in experiments on splenectomized male rats. It was found that the half-life of all the drugs increased and plasma clearance decreased. Total protein binding assessed by using congo red decreased to a certain degree after splenectomy. The main factor modifying pharmacokinetics of drugs following splenectomy is believed to be depression of biotransformation processes in the liver.