[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 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.

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.

Study of lot-to-lot reproducibilities of Bond Elut Certify and Clean Screen DAU mixed-mode solid-phase extraction columns in the extraction of drugs from whole blood.

The lot-to-lot reproducibilities of Bond Elut Certify and Clean Screen DAU columns are described. The recoveries of five test drugs obtained from twelve lots of Bond Elut Certify columns ranged from 84 to 104% with standard deviations of less than 9%. The recoveries of five test drugs obtained from six lots of Clean Screen DAU columns ranged from 81 to 103% with standard deviations of less than 7%. The 95% confidence intervals of the means as obtained by ANOVA demonstrate that there are no significant differences between the tested lots of Bond Elut Certify and Clean Screen DAU columns. Comparison of the two brands shows that both Bond Elut Certify and Clean Screen DAU columns are well acceptable for routine drug screening in systematic toxicological analysis, with a slightly higher overall recovery for the former.

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.

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.

Enantiospecific quantification of hexobarbital and its metabolites in biological fluids by gas chromatography/electron capture negative ion chemical ionization mass spectrometry.

A highly sensitive and specific assay based on gas chromatography/electron capture negative ion chemical ionization mass spectrometry has been developed for the analysis of the enantiomers of hexobarbital and its major metabolites in human urine and plasma. S-(+)-(5-2H3)hexobarbital and R-(-)-(5-2H3)hexobarbital were synthesized for clinical studies along with (+/-)-(1,5-2H6)hexobarbital and the deuterated major metabolites for use as internal and reference standards. Hexobarbital enantiomers and their metabolites were analyzed after pentafluorobenzyl and trimethylsilyl derivatization, following solid-phase extraction from plasma and urine. Intense negative ion spectra were observed for all of the derivatives. The base peak in the spectra corresponded to the M-pentafluorobenzyl anion [M-PFB]- except for 1,5-dimethylbarbituric acid, where M-. was the most abundant ion. The applicability of the method was demonstrated by following the plasma concentration-time profiles and urinary excretion in a male extensive metabolizer of mephenytoin who was given a pseudoracemic oral dose of hexobarbital containing equal 50 mg amounts of S-(+)-2(H0)hexobarbital and R-(-)-(2H3)hexobarbital. Marked stereoselective disposition was observed, with the R-(-)-enantiomer being more efficiently metabolized, primarily by alicyclic oxidation and ring cleavage.

High-performance liquid chromatographic method for the simultaneous determination of R-(-)- and S-(+)-hexobarbital in rat plasma.

The enantiospecific determination of R- and S-hexobarbital in rat plasma is described. The method involves liquid-liquid extraction of racemic hexobarbital from plasma, separation of the underivatized enantiomers by high-performance liquid chromatography on an alpha 1-acid glycoprotein column and ultraviolet detection. The mobile phase consists of a phosphate buffer (pH 5.4) containing 0.4% 2-propanol as organic modifier. An alpha 1-acid glycoprotein guard column is used to increase the lifetime of the analytical column. Heptabarbital is the achiral internal standard. With detection limits of ca. 0.05 microgram/ml for both R- and S-hexobarbital, the assay is suitable for pharmacokinetic studies of the enantiomers in rats.

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.

A simple and rapid high-pressure liquid chromatographic assay for pentobarbital and other barbiturates in serum.

A single extraction technique for measuring pentobarbital and other barbiturates in serum involved high-pressure liquid chromatography and UV detection yielding a sensitivity for pentobarbital of about 1 microgram/ml. We concluded that the assay provides a practical method for use in pharmacokinetic studies and in serum concentration monitoring in experimental animals.

Inhibition and induction of drug biotransformation in vivo by 8-methoxypsoralen: studies of caffeine, phenytoin and hexobarbital metabolism in the rat.

The effects of 8-methoxypsoralen (8-MOP) on drug metabolism in vivo were studied in catheterized rats. Rats were pretreated with a single i.p. injection of 5.4 or 27 mg/kg of 8-MOP, 30 min before an i.v. injection of either caffeine (CA; 10 mg/kg), hexobarbital (HB; 40 mg/kg), phenytoin (DPH; 15 mg/kg) or 5-(4'-hydroxyphenyl)-5-phenylhydantoin (HPPH; 15 mg/kg). Clearance of CA, HB and DPH, respectively (drugs eliminated primarily by phase-1 biotransformation), decreased from 0.25 +/- 0.02, 2.9 +/- 0.2 and 1.6 +/- 0.1 liters/kg/hr (means +/- S.E.) in control rats to 0.062 +/- 0.006, 0.65 +/- 0.15 and 0.09 +/- 0.03 liters/kg/hr in rats pretreated once with 27 mg/kg of 8-MOP. In contrast, the clearance of HPPH, which is eliminated primarily by glucuronidation, decreased only slightly from 1.3 +/- 0.1 liters/kg/hr in controls to 0.89 +/- 0.02 liters/kg/hr in rats pretreated with a single injection of 27 mg/kg of 8-MOP. Induction of drug metabolism by 8-MOP was studied in vivo in rats pretreated with 50 mg/kg/day of 8-MOP for 3 days and given an i.v. injection of CA, HB, DPH or HPPH 24 hr after their last pretreatment. This regimen increased the clearance of CA from 0.25 +/- 0.02 liters/kg/hr in controls to 1.08 +/- 0.04 liters/kg/hr in pretreated rats but had no significant effect on the elimination of HB, DPH and HPPH. Thus, acutely, 8-MOP is a potent, nonselective inhibitor of phase-1 metabolism in vivo. In contrast, chronically, it is a specific inducer of the metabolism of CA.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinetics of hexobarbital and dipyrone in critical care patients receiving high-dose pentobarbital.

The effect of pentobarbital treatment in a mean dose of 30 mg/kg/day on the clearance of hexobarbital (Evipan) and dipyrone (Novalgin) has been evaluated in critical care patients receiving a large number of drugs as comedication. Eleven patients treated with pentobarbital showed a hexobarbital half-life of 2.79 h and a total plasma clearance of 9.80 ml X min-1 X kg-1 as compared to 10 patients without pentobarbital administration in whom there was a significantly longer half life (6.92 h) and lower clearance (2.97 ml X min-1 X kg-1). The kinetics of hexobarbital were correlated with the urinary excretion of D-glucaric acid, a non-invasive parameter of drug metabolising activity. In 10 patients on pentobarbital, the total plasma clearance of N-4-methyl-aminoantipyrine, the active form of dipyrone, did not differ from that in 8 patients not receiving pentobarbital. As drug kinetics show great variability in these patients, it is difficult to discriminate enzyme induction from other mechanisms, for example competitive inhibition or changes in volume of distribution. In the presence of pentobarbital, however, induction of drug metabolising enzymes should be considered as a possible reason for the higher clearance of hexobarbital.

Effect of praseodymium chloride on liver microsomal enzymes of rats.

A single i.v. dose (5 mg/kg) of a light lanthanon, praseodymium, prolonged the duration of hexobarbital-induced sleep and zoxazolamine-induced paralysis, as well as it modified pharmacokinetic parameters of hexobarbital and zoxazolamine, in rats. Half-lives (t1/2) and area under the curve (AUC) were increased, while elimination coefficient (beta) and clearance (Cl) were decreased. However, in daily doses of 1 mg/kg i.p. for 15 days, praseodymium did not alter pharmacological effects and pharmacokinetic parameters. The in vitro hydroxylation of hexobarbital and zoxazolamine by liver microsomes was inhibited when the animals were treated previously with a single i.v. dose (5 mg/kg) of praseodymium chloride. In these animals, the amount of cytochromes P-450 and b5 were reduced significantly, whereas that of NADPH-cytochrome c reductase remained unchanged. The pretreatment of animals with phenobarbital normalized the microsomal enzyme impairment caused by praseodymium.

Pharmacokinetics of orally administered hexobarbital in plasma and saliva of healthy subjects.

Hexobarbital (HB) concentrations were determined in plasma and saliva of 8 healthy subjects, following oral administration of 500 mg HB-Na. Mean plasma half-lives were 3.2 +/- 0.1 h, and salivary half-lives 3.3 +/- 0.2 h. Mean plasma clearance was 22.9 +/- 2.3 1 h-1. There was a linear relationship between HB concentrations in saliva and plasma (r = 0.92). Mean salivary levels were 34 per cent of plasma levels. Salivary pH was constant throughout the experiment, 7.06 +/- 0.09. There was an inconsistent tendency of the saliva over plasma ratios to increase as a function of time. The percentage of protein binding calculated from saliva over plasma ratios was in reasonable agreement with in vitro data of equilibrium dialysis, 64.1 +/- 2.6 per cent and 65.9 +/- 0.8 per cent, respectively. The experiment was repeated in 4 subjects, and considerable intraindividual differences were shown to exist in saliva over plasma ratio, half-lives, and protein binding. It was concluded that HB elimination half-lives can relatively accurately be determined from salivary concentrations. Oral plasma clearance can only be estimated if the individual saliva over plasma ratios are known; this would require the taking of at least one blood sample during the experiment. When employing HB as a model substrate for drug metabolizing enzyme activity in vivo, the determination of its pharmacokinetic parameters, particularly oral plasma clearance as a reflection of cytochrome P-450 activity, cannot be achieved by taking saliva samples only.

Disposition of allylic oxidation pathway metabolites of racemic hexobarbital in the rat.

The pharmacokinetics in blood of the major metabolites of hexobarbital (HB), 3'-hydroxyhexobarbital (OH-HB) and 3'-ketohexobarbital (K-HB) were studied in rats. In addition urinary excretion of OH-HB and K-HB and 1,5-dimethylbarbituric acid (DMBA) was determined. Half-lives of OH-HB and K-HB were slightly longer than that of the parent drug. Urinary recovery of OH-HB, K-HB and DMBA following i.a. administration of OH-HB (75%) was more complete than the recovery following i.a. administration of K-HB (52%). Most probably further metabolism of K-HB takes place. Of K-HB, 41% was excreted renally, and 3.4% of K-HB reverted back to OH-HB. Of OH-HB, about 45% was excreted renally, following p.o. or i.a. administration. Since about 10% of both OH-HB and K-HB was converted to DMBA, it seems that the epoxide-diol pathway as proposed for HB also plays a minor role in the metabolism of OH-HB and K-HB. It is further concluded that measuring allylic pathway oxidation metabolites of HB does not improve the usefulness of HB as a model compound in the assessment of the activity of oxidative drug metabolizing activity.

Selected ion monitoring analysis of pseudoracemic hexobarbital and its major metabolites in blood and urine of rats.

A stereospecific synthesis of N1-(2H3)-labelled R(-)-hexobarbital is described. A sensitive and rapid selected ion monitoring assay procedure for pseudoracemic hexobarbital, consisting of equal amounts of S(+)-hexobarbital (1a) and (2H3)-R(-)-hexobarbital (1b) in 100 microliters blood samples of rats was developed. Both the parent enantiomers in blood and three major metabolites excreted in urine were quantified. An application of the method in rats is described, and the results are compared to previously obtained data of separately administered enantiomers.

[Characteristics of the ischemic disorders of xenobiotic metabolism in the liver of rats in the early and late stages of recovery]. / Kharakteristika ishemicheskikh narushenii metabolizma ksenobiotikov v pecheni krys na rannikh i otdalennykh étapakh vosstanovleniia.

It has been demonstrated in rat experiments that total ischemia of the liver leads to disorders of the metabolism of xenobiotics and endogenous substrates. Upset hexenal metabolism manifests in the prolongation of the hexenal-induced sleep and hexenal concentration elevation in blood plasma for 18 days of the postischemic period. Following exposure to ischemia liver microsomes show a decrease in the rate of amidopyrine, aniline and hydrocortisone hydroxylation. Hydrocortisone metabolism returns to normal by day 14, that of amidopyrine by day 21 of the postischemic period. Aniline metabolism gets disturbed to a greater degree, remaining 33.4% lower by day 21. It has been shown that the inducibility of microsomal monooxygenases is substantially restricted by days 7 and 14 of the postischemic period.