Analytical investigations of barbiturate poisoning--description of methods and a survey of results

Respiratory depression in rats induced by alcohol and barbiturate and rescue by ampakine CX717

Barbiturate use in conjunction with alcohol can result in severe respiratory depression and overdose deaths. The mechanisms underlying the additive/synergistic actions were unresolved. Current management of ethanol-barbiturate-induced apnea is limited to ventilatory and circulatory support coupled with drug elimination. Based on recent preclinical and clinical studies of opiate-induced respiratory depression, we hypothesized that ampakine compounds may provide a treatment for other types of drug-induced respiratory depression. The actions of alcohol, pentobarbital, bicuculline, and the ampakine CX717, alone and in combination, were measured via 1) ventral root recordings from newborn rat brain stem-spinal cord preparations and 2) plethysmographic recordings from unrestrained newborn and adult rats. We found that ethanol caused a modest suppression of respiratory drive in vitro (50 mM) and in vivo (2 g/kg ip). Pentobarbital induced an ∼50% reduction in respiratory frequency in vitro (50 μM) and in vivo (28 mg/kg for pups and 56 mg/kg for adult rats ip). However, severe life-threatening apnea was induced by the combination of the agents in vitro and in vivo via activation of GABA(A) receptors, which was exacerbated by hypoxic (8% O(2)) conditions. Administration of the ampakine CX717 alleviated a significant component of the respiratory depression in vitro (50-150 μM) and in vivo (30 mg/kg ip). Bicuculline also alleviated ethanol-/pentobarbital-induced respiratory depression but caused seizure activity, whereas CX717 did not. These data demonstrated that ethanol and pentobarbital together caused severe respiratory depression, including lethal apnea, via synergistic actions that blunt chemoreceptive responses to hypoxia and hypercapnia and suppress central respiratory rhythmogenesis. The ampakine CX717 markedly reduced the severity of respiratory depression.

Association of liver stiffness with hepatic expression of pharmacokinetically important genes in alcoholic liver disease

BACKGROUND

Enhanced drug elimination in alcoholics remains largely indefinable. In contrast, the reduced elimination of drugs in patients with advanced alcoholic liver disease (ALD) is normally owing to hepatic end-stage disease such as cirrhosis. We here study the mRNA expression of various hepatic drug metabolizing enzymes and transporters in association with liver stiffness (LS) being a novel noninvasive parameter for the assessment of cirrhosis to unravel the dynamic relationship between ALD and determinants of pharmacokinetics such as drug metabolizing enzymes and transporters.

METHODS

We quantified mRNA expression levels of various cytochrome P-450 isoenzymes (CYPs) and drug transporters in 26 liver specimens of chronic alcoholics and 5 controls by quantitative polymerase chain reaction. In addition, liver histology, clinical data, and LS evaluated by transient elastography (Fibroscan) were obtained.

RESULTS

Eighteen patients had a normal or moderate LS < 8 kPa (69.2%), while in the remaining 8 patients (30.7%) advanced F3 or F4 fibrosis could be established with an LS > 8 kPa. Overall, CYP3A4, CYP2E1, and solute carrier organic anion transporter 1B1 (SLCO1B1) were negatively correlated with increasing LS. CYPs and drug transporters tended to be up-regulated in alcoholics without advanced fibrosis (LS < 8.0 kPa) compared to healthy controls supporting data of boosted drug elimination in alcoholics without advanced ALD. However, in alcoholics with severely increased LS (>8 kPa), expression levels of CYP2E1, SLC22A2, and SLCO1B1 were significantly lower.

CONCLUSIONS

In conclusion, CYPs and drug transporters seem to be induced in chronic alcoholics without irreversible liver damage but decline in case of manifest cirrhosis. Our study also suggests that noninvasive measurements of LS could be useful for pharmacokinetic predictions and individualized pharmacotherapy.

Interactions between alcohol and other drugs

More than 75% of people age 65 and older use medications. Of the drugs most commonly used by older people, many have potential to interact adversely with alcohol. The absorption, distribution, metabolism, and effects of drugs or alcohol may be affected. The major adverse clinical outcomes of drug-alcohol interactions are altered blood levels of the medication or of alcohol, liver toxicity, gastrointestinal inflammation and bleeding, sedation and delirium, disulfiram-like reactions, and interference with the desired effect of medications. Since alcohol is commonly used by elderly people, educating patients about the potential for these interactions should be a routine part of health care visits.

Mechanisms of ethanol-drug-nutrition interactions

Mechanisms of the toxicologic manifestations of ethanol abuse are reviewed. Hepatotoxicity of ethanol results from alcohol dehydrogenase-mediated excessive hepatic generation of nicotinamide adenine dinucleotide and acetaldehyde. It is now recognized that acetaldehyde is also produced by an accessory (but inducible) pathway, the microsomal ethanol-oxidizing system, which involves a specific cytochrome P450. It generates oxygen radicals and activates many xenobiotics to toxic metabolites, thereby explaining the increased vulnerability of heavy drinkers to industrial solvents, anesthetics, commonly used drugs, over-the-counter medications and carcinogens. The contribution of gastric alcohol dehydrogenase to the first pass metabolism of ethanol and alcohol-drug interactions is now recognized. Alcohol also alters the degradation of key nutrients, thereby promoting deficiencies as well as toxic interactions with vitamin A and beta-carotene. Conversely, nutritional deficits may affect the toxicity of ethanol and acetaldehyde, as illustrated by the depletion in glutathione, ameliorated by S-adenosyl-L-methionine. Other supernutrients include polyenylphosphatidylcholine, shown to correct the alcohol-induced hepatic phosphatidylcholine depletion and to prevent alcoholic cirrhosis in non-human primates. Thus, a better understanding of the pathology induced by ethanol has now generated improved prospects for therapy.

CNS depressant effects of volatile organic solvents

Volatile chemicals used widely as solvents can produce acute effects on the nervous system and behavior after inhalation exposure, and many are subject to abuse. This review considers the nature of the acute effects of volatile organic solvents by comparing their actions to those of classical CNS depressant drugs such as the barbiturates, benzodiazepines and ethanol. Like CNS depressant drugs, selected inhalants have been shown to have biphasic effects on motor activity, disrupt psychomotor performance, have anticonvulsant effects, produce biphasic drug-like effects on rates of schedule-controlled operant behavior, increase rates of punished responding, enhance the effects of depressant drugs, serve as reinforcers in self-administration studies and share discriminative stimulus effects with barbiturates and ethanol. Toluene and 1,1,1-trichloroethane, as well as subanesthetic concentrations of halothane, have been the most extensively studied; however, it is unclear whether important differences may exist among solvents in their ability to produce a depressant profile of acute effects. The possibility that selected solvents can have acute effects similar to those of depressant drugs may shed light on the nature of their acute behavioral toxicology and on their abuse.

Quantification of the interaction between barbiturates and alcohol and interpretation of fatal blood concentrations

Barbiturates and alcohol are frequently found in combination in cases of accidental or intentional fatal self-poisoning. Unfortunately, the lack of any precise knowledge concerning their interaction creates difficult problems when an interpretation of toxicological data is sought. 1 In the following work the joint action of single barbiturates and alcohol is examined and a means of quantifying it is presented. 2 The effects of different amounts of alcohol on fatal amylobarbitone, butobarbitone, pentobarbitone, phenobarbitone and quinalbarbitone blood concentrations are compared. 3 Combined alcohol-barbiturate blood concentration curves connecting those concentration pairs equally effective in causing death are used to quantify the increase in toxicity. The quantitative effects of alcohol appear to be greater with the shorter- and longer-acting barbiturates than with the intermediate-acting derivatives. The different modes of interaction are discussed in terms of the physico-chemical and pharmacokinetic properties of the drugs.

Effect of ethanol on drug levels in blood in fatal cases

The cumulative frequency distributions of postmortem blood levels of four centrally-acting drugs (pentobarbitone, amitriptyline, chlormethiazole and dextropropoxyphene) have been derived from fatalities involving either the named drug only or the drug in association with ethanol only. For each drug, the presence of ethanol markedly reduced the concentration at which a given proportion of fatalities occurred.

Rapid identification of drugs in the overdosed patient

A rapid analytical procedure is described for a variety of drugs that could be present in the overdosed patient. The technique used gives quantitative results for most of the drugs analyzed in serum using gas chromatography and incorporates thin-layer chromatography and spot tests for drug confirmation. The procedure is novel for it relies on the initial extraction of acidics, basics, and neutrals from serum acidified with hydroxhloric acid.

Barbiturate blood levels found at necropsy in proven cases of acute barbiturate poisoning

In order to determine whether blood barbiturate levels could be used to ascertain that death had been caused by barbiturate overdose, samples of blood from 128 subjects of coroners' necropsies were examined for barbiturate content. Sixty of these were well authenticated cases of barbiturate overdosage, and barbiturates were implicated, together with other factors such as alcohol and carbon monoxide, in a further 16 cases. The remaining 52 cases were of an eliminatory nature, 10 of which had low barbiturate blood levels considered to be within the therapeutic range.The results indicate that when the accepted levels producing loss of consciousness are exceeded, and maintained, death will ensue if treatment is not given. These results may be of value in assessing findings in necropsies requested by the coroner, and are in no way applicable to the living patient in whom it is well established that recovery from higher blood levels may take place if adequate treatment is available.

Toxicity of ethanol-barbiturate mixtures

The simultaneous administration of ethanol at doses of either 2, 3, or 4 g/kg intraperitoneally produced a dose-related decrease in the intraperitoneal LD50 for thiopentone, pentobarbitone, amylobarbitone, phenobarbitone and barbitone in rats. The most marked ethanol-barbiturate interaction was with the long-acting, poorly metabolized, less potent barbiturates phenobarbitone and barbitone. Similarly, a non-hypnotic dose of ethanol (3 g/kg, i.p.) produced a much greater prolongation of the sleeping time with non-hypnotic doses of phenobarbitone and barbitone, than with threshold doses of the shorter acting barbiturates. Various postulates are advanced to explain the underlying mechanism of the barbiturate-ethanol interaction.

The relation between primidone and phenobarbitone blood levels

A dose of primidone or one fifth of the same weight of phenobarbitone produced equal levels of phenobarbitone in the blood.