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PubMed1986

Facilitation of recurrent inhibition in rat hippocampus by barbiturate and related nonbarbiturate depressant drugs.

The effects of anticonvulsant, anesthetic and convulsant barbiturates and of related depressant drugs were characterized on excitatory and inhibitory synaptic transmission in slices of rat hippocampus. The duration of recurrent GABAergic inhibition was increased by all of the drugs tested, including the convulsant barbiturate 5-ethyl-5-[1,3-dimethylbutyl]barbituric acid, anesthetic barbiturates such as pentobarbital and nonbarbiturate anesthetics such as (+)-etomidate. Several barbiturates, including phenobarbital and (+)-mephobarbital facilitated inhibition, but the maximal responses to these agents were significantly less than with pentobarbital. In general, there was a good correspondence between the potencies of these drugs in facilitating inhibition and their previously reported abilities to regulate binding at the gamma-aminobutyric acid/benzodiazepine/barbiturate receptor complex. In addition to facilitating recurrent GABAergic inhibition, at successively higher doses most of these drugs induced direct depression of the population spike response, field excitatory postsynaptic potential and presynaptic fiber spike. 5-Ethyl-5-[1,3-dimethylbutyl]barbituric acid, (+)-mephobarbital and pentobarbital facilitated excitatory synaptic transmission at the Schaffer collateral/commissural synapses on the CA1 pyramidal neurons at low doses, but caused depression at higher doses. The net effects observed with each drug tested (facilitation/depression of excitatory transmission, enhancement of GABAergic inhibition) correlated well with the behavioral effects of these agents in vivo.

Animals↗
PubMed1976

Metabolism, distribution and anticonvulsant properties of N,N'- dimethoxymethyl-phenobarbital in the rat.

The in vivo metabolism of N,N'-dimethoxymethyl phenobarbital (DMMP) and the anticonvulsant properties of its metabolites were studied in the rat. At 10 and 30 minutes after i.p. administration, DMMP (ethyl-1-14C) represented less than 3% of plasma radioactivity, whereas N-monomethoxymethyl phenobarbital (MMP) was 78 and 75%, respectively, phenobarbital (PB) 12 and 20%, apparent mephobarbital 6 and 2% and less than 5% of the radioactivity remained at the origin. Peak levels of MMP were reached at 30 minutes in liver and 60 minutes in plasma and brain. At 4 hours, MMP had declined to 7% in plasma and was not detected in brain while PB rose to 93% of total 14C in plasma and brain. SKF-525A blocked (90%) the in vivo conversion of DMMP to MMP and completely inhibited the formation of PB, apparent mephobarbital and unidentified polar metabolites. MMP after oral administration was effective against maximum electroshock seizures at a time when brain levels of PB derived from MMP were insufficient to account for the total observed protection. However, MMP appears less potent than PB against pentylenetetrazol seizures.

Animals↗
PubMed1987

Identification and synthesis of O-methylcatechol metabolites of phenobarbital and some N-alkyl derivatives.

5-Ethyl-5-(4-hydroxy-3-methoxyphenyl) barbituric acid was identified as a new, minor metabolite of phenobarbital in man. The identity of this O-methylcatechol metabolite was confirmed by an unequivocal chemical synthesis, and by GC-MS studies. Mephobarbital and the 1,3-dimethyl, 1-ethyl, and 1,3-diethyl analogues of phenobarbital yielded the corresponding N-alkylated O-methylcatechol metabolites, all of which were confirmed by synthesis. The N-alkyl barbiturates each gave additionally at least one O-methylcatechol metabolite in which N-dealkylation had occurred. These metabolites accounted for approximately 1-5% of the orally administered dose in man.

Catechols↗
PubMed1996

Distinct effects of phenobarbital and its N-methylated derivative on liver cytochrome P450 induction.

The relationship between barbiturate structures and their effects on induction of rat cytochrome P450 forms was studied in primary cultured hepatocytes. Treatment of hepatocytes cultured on matrigel with 1 mM barbital, N-methylbarbital, cyclobarbital, hexobarbital, phenobarbital (PB), or mephobarbital (N-methyl-PB) resulted in increased amounts of CYP2B1/2 and CYP2C6 forms. Microsomal CYP3A content was also enhanced by treatment with these barbiturates, except for barbital. Although no relationship was observed between the levels of CYP2B1/2 and CYP3A, ratios of CYP3A/CYP2B1 plus CYP2B2 contents were invariably higher with hepatocytes treated with N-methylated barbiturates than with the nonmethylated analogs. Consistent results were also observed in vivo in rats treated with PB and N-methyl-PB. These results indicate the difference in the structure requirement for induction of CYP2B and CYP3A. In addition, N-methyl-PB was found to suppress PB-mediated induction of CYP2B1. Hepatic levels of CYP2B1 mRNA and protein were increased by treatment with PB or N-methyl-PB alone, but decreased by cotreatment with 1 mM PB and N-methyl-PB. The suppression has been shown to occur at the transcriptional level of the CYP2B1 gene by using a chloramphenicol acetyltransferase reporter-CYP2B1 fused gene system.

Animals↗
PubMed1979

Enhancement of GABA-mediated postsynaptic inhibition in cultured mammalian spinal cord neurons: a common mode of anticonvulsant action.

Murine spinal cord neurons grown in dissociated cell culture were used to study the effects of barbiturate (phenobarbital, mephobarbital) and benzodiazepine (diazepam, chlordiazepoxide( anticonvulsants on amino acid responses. Both types of anticonvulsant augmented GABA-mediated postsynaptic inhibition without augmenting beta-alanine or glycine-mediated postsynaptic inhibition. Barbiturates, but not benzodiazepines, antagonized glutamate-mediated postsynaptic excitation. Augmentation of GABA-mediated inhibition by the anticonvulsants should contribute to their anticonvulsant action; antagonism of glutamate-mediated excitation by barbiturates should also contribute to their anticonvulsant action and could be at least in part responsible for their sedative actions.

Animals↗
PubMed1998

Simultaneous determination of methylphenobarbital enantiomers and phenobarbital in human plasma by on-line coupling of an achiral precolumn to a chiral liquid chromatographic column.

A fully automated liquid chromatographic (LC) method for the simultaneous determination of methylphenobarbital enantiomers and phenobarbital in human plasma has been developed. The method is based on the use of a precolumn packed with an internal-surface reversed-phase packing material (LiChrospher ADS) for sample clean-up coupled to LC analysis on a cellulose tris(4-methylbenzoate) based chiral stationary phase (Chiralcel OJ-R). A 100-microliter plasma sample was injected directly on the precolumn packed with LiChrospher RP-18 ADS using a mixture of pH 5.0 phosphate buffer-methanol (97:3, v/v) as washing liquid. The analytes were then eluted in the back-flush mode with the LC mobile phase. The enantiomeric separation of methylphenobarbital was achieved on Chiralcel OJ-R). The retention times were modelled using a D-optimal design with ten experimental points in order to optimise the LC mobile phase for the separation of phenobarbital from the enantiomers of mephobarbital. The factors selected were the acetonitrile content, the pH and the sodium perchlorate concentration in the mobile phase. A Derringer's desirability function was used to find an optimal and robust solution within the experimental domain. The mobile phase selected consisted of a mixture of pH 7.0 phosphate buffer-acetonitrile (60:40, v/v). The elution profiles of phenobarbital, methylphenobarbital and blank plasma samples on the precolumn and the time needed for analyte transfer from the precolumn to the analytical column were then determined. Finally, the method developed was validated.

Chromatography, Liquid↗
PubMedDate not supplied

Cerebral protection with barbiturates: relation to anesthetic effect.

The effect of racemic mephobarbital and its optical isomers on survival time of mice exposed to 5% O2 was studied. There was an increase in survival time from 4.2 minutes to 12.6 minutes for 100 mg/kg of the anesthetically active (-) isomer and the racemic form, but no increase for 100 mg/kg of the inactive (+) isomer. Since it has been shown that there is no difference in brain concentrations between the isomers, we conclude that the barbiturate protective effect is bound to the anesthetic effect. All mice convulsed, and since the non-anesthetized animals convulsed earlier and stronger than the anesthetized, it was possible that barbiturate protection was accounted for by its anticonvulsant effects. Diazepam 7.5 mg/kg, while reducing convulsions to the same degree as barbiturates without producing anesthesia, only increased survival time to 6.2 minutes. Thus, the barbiturate protective effect is distinct from the anticonvulsant effect. It seems to be bound to a stereospecific receptor for both protection and anesthesia.

Anesthetics↗
PubMed2000

Prediction of adsorption from multicomponent solutions by activated carbon using single-solute parameters.

The adsorption of 3 barbiturates--phenobarbital, mephobarbital, and primidone--from simulated intestinal fluid (SIF), without pancreatin, by activated carbon was studied using the rotating bottle method. The concentrations of each drug remaining in solution at equilibrium were determined with the aid of a high-performance liquid chromatography (HPLC) system employing a reversed-phase column. The competitive Langmuir-like model, the modified competitive Langmuir-like model, and the LeVan-Vermeulen model were each fit to the data. Excellent agreement was obtained between the experimental and predicted data using the modified competitive Langmuir-like model and the LeVan-Vermeulen model. The agreement obtained from the original competitive Langmuir-like model was less satisfactory. These observations are not surprising because the competitive Langmuir-like model assumes that the capacities of the adsorbates are equal, while the other 2 models take into account the differences in the capacities of the components. The results of these studies indicate that the adsorbates employed are competing for the same binding sites on the activated carbon surface. The results also demonstrate that it is possible to accurately predict multicomponent adsorption isotherms using only single-solute isotherm parameters. Such prediction is likely to be useful for improving in vivo/in vitro correlations.

Adsorption↗
PubMed2002

Prediction of adsorption from multicomponent solutions by activated carbon using single-solute parameters. Part II--Proposed equation.

Prediction of multicomponent adsorption is still one of the most challenging problems in the adsorption field. Many models have been proposed and employed to obtain multicomponent isotherms from single-component equilibrium data. However, most of these models were based on either unrealistic assumptions or on empirical equations with no apparent definition. The purpose of this investigation was to develop a multicomponent adsorption model based on a thermodynamically consistent equation, and to validate that model using experimental data. Three barbiturates--phenobarbital, mephobarbital, and primidone--were combined to form a ternary system. The adsorption of these barbiturates from simulated intestinal fluid (without pancreatin) by activated carbon was studied using the rotating bottle method. The concentrations, both before and after the attainment of equilibrium, were determined with a high-performance liquid chromatography system employing a reversed-phase column. The proposed equation and the competitive Langmuir-like equation were both fit to the data. A very good correlation was obtained between the experimental data and the calculated data using the proposed equation. The results obtained from the original competitive Langmuir-like model were less satisfactory. These results suggest that the proposed equation can successfully predict the trisolute isotherms of the barbituric acid derivatives employed in this study.

Adsorption↗
PubMed1979

Anticonvulsant and anesthetic barbiturates: different postsynaptic actions in cultured mammalian neurons.

Mammalian spinal cord neurons were grown in dissociated cell culture and used to study the effects of the anticonvulsant barbiturates phenobarbital and mephobarbital, and the anesthetic barbiturates pentobarbital, secobarbital, and 1,3-dimethyl-butylethyl barbituric acid on amino acid responses and neuronal membrane properties. All barbiturates augmented responses to GABA and diminished glutamate (GLU) responses, but the anesthetic barbiturates were more potent. The anesthetic barbiturates directly depressed excitability by increasing membrane conductance, an effect reversed by the GABA antagonists picrotoxin and penicillin. Anticonvulsant barbiturates, however, had only minimal GABA-mimetic inhibitory action at high doses. Modulation of synaptic events mediated by GABA and GLU might contribute to barbiturate anticonvulsant activity; and direct GABA-mimetic inhibition, combined with similar modulation of synaptic transmission, might underlie barbiturate anesthesia.

Animals↗
PubMed1982

Effects of barbiturates on the decerebrate rigidity in rats.

Effects of barbiturates (phenobarbital, mephobarbital, pentobarbital, hexobarbital and amobarbital) on the tonic and phasic responses of forelimbs were studied in the rats in which rigidity was induced by means of anemic decerebration. The inhibitory pattern of the tonic and phasic responses to phenobarbital was different from those to the other barbiturates, i.e. phenobarbital gradually inhibited both tonic and phasic responses, whereas other barbiturates suppressed significantly only the tonic response immediately after the administration of a relatively low dose (10 mg/kg) but hardly inhibited the phasic response unless at higher doses (20 and 40 mg/kg). Possible involvement of GABA-system in the inhibitory action of phenobarbital and pentobarbital on the rigidity was investigated. Since inhibition of the phasic response to pentobarbital was potentiated by the pretreatment of animals with carboxymethoxylamine hemihydrochloride (AOAA) and suppressed by the pretreatment with semicarbazide, it was suggested that GABAergic mechanism may be involved in the particular inhibition of phasic response to pentobarbital. However, the inhibitory action of phenobarbital appeared to be independent of GABA-system.

Aminooxyacetic Acid↗
PubMed1983

Effect of acetazolamide on the anticonvulsant potency of several antiepileptic drugs in mice.

Effect of acetazolamide (AZA) on the anticonvulsant potency of several antiepileptics was investigated in mice by maximal electroshock seizure test. By the coadministration of AZA, a remarkable increase in the anticonvulsant activity was brought about not only for the barbiturates including barbital (BA), mephobarbital (MB) and metharbital (MET), but also for the other antiepileptics such as phenytoin (PHT), valproic acid (VPA) and trimethadione (TMO). This potentiating effect of AZA, however, was relatively weak for PHT, MET and TMO (about 2.5 fold) in contrast to those for phenobarbital (PHB), BA, MB and VPA (4-5 fold). The brain-serum concentration ratio (B/S) of PHB was elevated by the coadministration of AZA, while the B/S of PHT was not changed. Thus it was inferred that the difference in the potentiating effect of AZA on the activity of the antiepileptics was due to the difference in its effect on the brain levels of the antiepileptic drugs. However, the potentiating effect of AZA was still observed for PHT, VPA and MET, as well as PHB, in reserpinized mice. Therefore, some pharmacodynamic effect of AZA other than its increasing effect on the brain levels of the antiepileptic drugs may partly contribute to the potentiation of the activity of the antiepileptic drugs.

Acetazolamide↗
PubMed1975

Flash-heater ethylation of some antiepileptic drugs.

We describe a modification of the MacGee method [Anal. Chem. 42, 421 (1970)] for rapid determination of phenytoin (diphenylhydantoin) in plasma by gas-liquid chromatography, in which an ethylaing reagent is used instead of the more common methylating reagents. With this modification, several N-methylated antiepileptic drugs can be separated from their demethylated metabolites. Our results agree well with those of Butler and Waddell [Neurology 8, 106 (1958)], who showed that in patients receiving the N-methylated compounds mephenytoin and mephobarbital, the N-demethylated products, 5-ethyl-5-phenylhydantoin and phenobarbital are found in higher concentrations in plasma than are their respective parent drugs. The method is also useful for routine determinations of phenobarbital, primidone, and phenytoin in serum, cerebrospinal fluid, or saliva.

Alkylation↗
PubMed1985

Characterization of barbiturate-stimulated chloride efflux from rat brain synaptoneurosomes.

Membrane chloride (Cl-) permeability was studied in a novel subcellular brain preparation, the synaptoneurosome. Using a radioactive tracer exchange technique, Cl- transport was determined by measuring 36Cl- efflux from rat cerebral cortical synaptoneurosomes. Barbiturates increased 36Cl- efflux in a dose-dependent manner with the following relative order of potency: 5-(1,3-dimethylbutyl)-5-ethyl barbituric acid ((-)-DMBB) greater than pentobarbital greater than secobarbital greater than (+)-DMBB greater than hexobarbital greater than amobarbital greater than mephobarbital. Phenobarbital and barbital were virtually inactive. A good correlation was observed between the potencies of these barbiturates in stimulating 36Cl- efflux and their anesthetic potencies in mice (r = 0.90, p less than 0.01) and their abilities to enhance [3H] diazepam binding to brain membranes (r = 0.77, p less than 0.05). The effect of pentobarbital in enhancing 36Cl- efflux was reversed by the gamma-aminobutyric acid (GABA) antagonists picrotoxin and bicuculline. Picrotoxin and bicuculline both decreased 36Cl- efflux in the absence of pentobarbital, suggesting the presence of endogenous GABA. Incubation of synaptoneurosomes with 4,4'-di-isothiocyano- or dinitro-2,2'-disulfonic acid stilbene, inhibitors of anion transport, also decreased both basal and pentobarbital-induced 36Cl- efflux. Pentobarbital (500 microM) was most effective in inducing 36Cl- efflux in the cerebellum, hippocampus, and cortex (23.7, 23.6, and 22.5%, respectively), and was less effective in stimulating 36Cl- efflux in the striatum (15.1%) and pons-medulla (6.2%). The relative efficacy of pentobarbital in enhancing 36Cl- efflux among these various brain regions was highly correlated (r = 0.96, p 0.01) with the relative densities of [35S]-t-butylbicyclophosphorothionate-binding sites, a measure of GABA-gated Cl- channel density.(ABSTRACT TRUNCATED AT 250 WORDS)

Amobarbital↗
PubMed2000

Barbiturates for acute traumatic brain injury.

BACKGROUND: Raised intracranial pressure (ICP) is an important complication of severe brain injury, and is associated with a high mortality rate. Barbiturates are believed to reduce intracranial pressure by suppressing cerebral metabolism, thus reducing cerebral metabolic demands and cerebral blood volume. However, barbiturates also reduce blood pressure and therefore may adversely effect cerebral perfusion pressure. OBJECTIVES: To assess the effects of barbiturates in reducing raised intracranial pressure, mortality and morbidity in people with acute traumatic brain injury. To quantify any side effects resulting from the use of barbiturates. SEARCH STRATEGY: The review draws largely on the search strategy developed for the Cochrane Injuries Group as a whole. However, in addition the Cochrane Library was searched in December 1996 using the text terms "barbiturate*," "pentobarb*," "phenobarb*," "head," and "brain." An updated search was done in April 1999. SELECTION CRITERIA: Randomised or quasi randomised trials of any one or more of the barbiturate class of drugs (amobarbital, barbital, hexobarbital, mephobarbital, methohexital, murexide, pentobarbital, phenobarbital, secobarbital, thiobarbiturate) where study participants had a clinically diagnosed acute traumatic brain injury of any severity. DATA COLLECTION AND ANALYSIS: The reviewer extracted the data and assessed the quality of allocation concealment in the trials. MAIN RESULTS: The pooled relative risk for death (barbiturate vs no barbiturate) was 1.09 (95%CI 0.81 to 1.47). The pooled effect of barbiturates on adverse neurological outcome, measured using the Glasgow Outcome Scale (death, persistent vegetative state or severe disability) was 1.15 (95% 0.81 to 1.64). Two studies examined the effect of barbiturate therapy on intracranial pressure. In the study by Eisenberger et al, a smaller proportion of patients in the barbiturate group had uncontrolled ICP (68% vs 83%). The relative risk for uncontrolled ICP was 0.81 (95%CI 0.62 to 1.06). Similarly, in the study by Ward et al, mean ICP was lower in the barbiturate treated group. Barbiturate therapy results in an increase in the occurrence of hypotension (RR=1.80 95%CI 1.19 to 2.70). For every four patients treated one will develop clinically significant hypotension. Mean body temperature was significantly lower in the barbiturate treated group. Schwartz et al compared pentobarbital with mannitol in the control of intracranial pressure. Pentobarbital was less effective than mannitol for control of raised ICP. 68% of patients in the pentobarbital treated group required a second drug for the treatment of raised intracranial pressure compared to 39% in the mannitol treated group (RR=1.75 95%CI 1.05 to 2.92). There was no substantial difference in mortality between the two study groups (RR=1.18 95%CI 0.73 to 1.92). REVIEWER'S CONCLUSIONS: There is no evidence that barbiturate therapy in patients with acute severe head injury improves outcome. Barbiturate therapy results in a fall in blood pressure in 1 in 4 treated patients. The hypotensive effect of barbiturate therapy will offset any ICP lowering effect on cerebral perfusion pressure.

Barbiturates↗
PubMed1989

Genetic polymorphism in drug oxidation.

Of the two clearly established drug oxidation polymorphisms, only the one referred to as debrisoquine polymorphism affects many drugs. The only known polymorphic substrates of mephenytoin hydroxylase are mephenytoin and mephobarbital. Relatively recently discovered drug substrates of debrisoquine hydroxylase are propafenone, diltiazem, and codeine. The list of substrates contains 28 items. The fate of slightly less than half of these is clinically affected in poor metabolizers, and several of the latter drugs are no longer marketed. There are many reasons why a failure of metabolism may not alter the fate of a drug sufficiently to affect its clinical use. Of interest and clinical importance is the inhibition of debrisoquine hydroxylase by inhibitors such as quinidine and by some neuroleptics; also the simultaneous use of two substrates has led to serious toxicity by mutual metabolic inhibition. The study of these oxidation polymorphisms has been instructive not only for formal pharmacogenetics but also for the understanding of problems of therapy in patients without genetic defects.

Animals↗
PubMed1984

Interaction of barbiturates with adenosine receptors in rat brain.

The effects of barbiturates on radioligand binding to inhibitory Ri adenosine receptors of rat brain membranes were investigated. Binding of the adenosine receptor agonist (-)N6-phenylisopropyl[3H]adenosine and the antagonist 1,3-diethyl-8-[3H]phenylxanthine was inhibited by several barbiturates. This inhibition was concentration-dependent and occurred in the range of pharmacologically effective concentrations. Pentobarbital was the most potent of the barbiturates tested with a Ki of 92 mumol/l. The (+)isomers of hexobarbital and mephobarbital were more potent than the respective (-)isomers. Barbituric acid itself did not displace either radioligand in concentrations up to 1 mmol/l. The inhibitory effect of pentobarbital was reversed by a single wash of membranes preincubated with the barbiturate. The presence of pentobarbital caused a decrease of the affinity of the receptor for the antagonist radioligand but did not alter the number of binding sites, suggesting a competitive antagonism. The effects of pentobarbital on radioligand binding to the receptor were not changed by the presence of picrotoxinin nor by the absence of chloride ions. This indicates that they are not mediated via the picrotoxinin binding site. The barbiturates could not be classified as either agonists or antagonists at the Ri adenosine receptor. The presence of GTP did not influence the inhibition of radioligand binding by pentobarbital; this is also observed for antagonists, whereas the affinity of agonists is markedly reduced by GTP. Binding of antagonists to the receptor is enthalpy-driven; the interaction of pentobarbital with the receptor was entropy-driven and the same was true for agonists.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗
PubMed1983

Optimization of a novel two-phase potentiometric titration method of barbiturates with mercury (II). Part II: Experimental evaluation.

A two-phase potentiometric titration procedure of barbiturates with mercury(II) was developed. The composition of the formed mercury-barbiturate complexes was elucidated by infrared spectrometry. In the new titration procedure the barbituric acid derivative is dissolved in an aqueous borate buffer. An organic phase consisting of chloroform and benzyl alcohol is added, and the vigorously stirred contents of the titration vessel are titrated by a mercury(II) nitrate solution. In the potentiometric determination of the end-point a rotating mercury electrode is used as an indicator electrode that also serves as an efficient stirrer. The two-phase procedure was compared with a one-phase mercurimetric potentiometric titration in borate buffer and with the potentiometric titration by sodium hydroxide in an ethanol-water solution. The proposed two-phase procedure is superior to both methods because lower concentrations of barbiturates (10(-3) - 10(-4) M) can be determined successfully. The one-phase procedure suffers from systematic errors, while the titration with sodium hydroxide is less precise at concentration levels of the barbiturates prevailing in content uniformity studies. By the two-phase procedure the direct titration of phenobarbital and mephobarbital in a dry mix of tablet excipients was possible with a relative standard deviation smaller than 1.5 percent.

Barbital↗