Dexmedetomidine, Diazepam, and Propranolol in the Treatment of Ethanol Withdrawal Symptoms in the Rat

The Amygdala Noradrenergic System Is Compromised With Alcohol Use Disorder

BACKGROUND

Alcohol use disorder (AUD) is a leading preventable cause of death. The central amygdala (CeA) is a hub for stress and AUD, while dysfunction of the noradrenaline stress system is implicated in AUD relapse.

METHODS

Here, we investigated whether alcohol (ethanol) dependence and protracted withdrawal alter noradrenergic regulation of the amygdala in rodents and humans. Male adult rats were housed under control conditions, subjected to chronic intermittent ethanol vapor exposure to induce dependence, or withdrawn from chronic intermittent ethanol vapor exposure for 2 weeks, and ex vivo electrophysiology, biochemistry (catecholamine quantification by high-performance liquid chromatography), in situ hybridization, and behavioral brain-site specific pharmacology studies were performed. We also used real-time quantitative polymerase chain reaction to assess gene expression of α1B, β1, and β2 adrenergic receptors in human postmortem brain tissue from men diagnosed with AUD and matched control subjects.

RESULTS

We found that α1 receptors potentiate CeA GABAergic (gamma-aminobutyric acidergic) transmission and drive moderate alcohol intake in control rats. In dependent rats, β receptors disinhibit a subpopulation of CeA neurons, contributing to their excessive drinking. Withdrawal produces CeA functional recovery with no change in local noradrenaline tissue concentrations, although there are some long-lasting differences in the cellular patterns of adrenergic receptor messenger RNA expression. In addition, postmortem brain analyses reveal increased α1B receptor messenger RNA in the amygdala of humans with AUD.

CONCLUSIONS

CeA adrenergic receptors are key neural substrates of AUD. Identification of these novel mechanisms that drive alcohol drinking, particularly during the alcohol-dependent state, supports ongoing new medication development for AUD.

Linking Ethanol-Addictive Behaviors With Brain Catecholamines: Release Pattern Matters

Using a variety of animal models that simulate key features of the alcohol use disorder (AUD), remarkable progress has been made in identifying neurochemical targets that may contribute to the development of alcohol addiction. In this search, the dopamine (DA) and norepinephrine (NE) systems have been long thought to play a leading role in comparison with other brain systems. However, just recent development and application of optogenetic approaches into the alcohol research field provided opportunity to identify neuronal circuits and specific patterns of neurotransmission that govern the key components of ethanol-addictive behaviors. This critical review summarizes earlier findings, which initially disclosed catecholamine substrates of ethanol actions in the brain and shows how the latest methodologies help us to reveal the significance of DA and NE release changes. Specifically, we focused on recent optogenetic investigations aimed to reveal cause-effect relationships between ethanol-drinking (seeking and taking) behaviors and catecholamine dynamics in distinct brain pathways. These studies gain the knowledge that is needed for the better understanding addiction mechanisms and, therefore, for development of more effective AUD treatments. Based on the reviewed findings, new messages for researches were indicated, which may have broad applications beyond the field of alcohol addiction.

Therapeutic potential of ketamine for alcohol use disorder

Excessive alcohol consumption is involved in 1/10 of deaths of U.S. working-age adults and costs the country around $250,000,000 yearly. While Alcohol Use Disorder (AUD) pathology is complex and involves multiple neurotransmitter systems, changes in synaptic plasticity, hippocampal neurogenesis, and neural connectivity have been implicated in the behavioral characteristics of AUD. Depressed mood and stress are major determinants of relapse in AUD, and there is significant comorbidity between AUD, depression, and stress disorders, suggesting potential for overlap in their treatments. Disulfiram, naltrexone, and acamprosate are current pharmacotherapies for AUD, but these treatments have limitations, highlighting the need for novel therapeutics. Ketamine is a N-methyl-D-Aspartate receptor antagonist, historically used in anesthesia, but also affects other neurotransmitters systems, synaptic plasticity, neurogenesis, and neural connectivity. Currently under investigation for treating AUDs and other Substance Use Disorders (SUDs), ketamine has strong support for efficacy in treating clinical depression, recently receiving FDA approval. Ketamine's effect in treating depression and stress disorders, such as PTSD, and preliminary evidence for treating SUDs further suggests a role for treating AUDs. This review explores the behavioral and neural evidence for treating AUDs with ketamine and clinical data on ketamine therapy for AUDs and SUDs.

Noradrenergic targets for the treatment of alcohol use disorder

The role of norepinephrine (NE) in the development of alcohol use disorder (AUD) has been studied over the past several decades. However, the NE system has been largely ignored for many years as a potential target for medication development for AUD. More recently, preclinical and clinical studies have demonstrated the potential value of targeting NE signaling for developing new pharmacological treatments for AUD. This review contributes to a special issue of Psychopharmacology focused on promising targets for alcohol addiction. Specifically, this review coalesces preclinical and clinical neuroscience that re-evaluate the noradrenergic system, and in particular the alpha-1 receptor, as a potential target for AUD.

An assessment of the utilization of the preclinical rodent model literature in clinical trials of putative therapeutics for the treatment of alcohol use disorders

OBJECTIVE

Rodent models of Alcohol Use Disorders (AUD) are used extensively by preclinical researchers to develop new therapeutics for the treatment of AUD. Although these models play an important role in the development of novel, targeted therapeutics, their role in bringing therapeutics to clinical trials is unclear, as off-label use of existing medications not approved for the treatment of AUD is commonly seen in the clinic and clinical trials.

METHOD

In the current study, we used the Clinicaltrials.gov database to obtain a list of drugs that have been tested for efficacy in a clinical trial between 1997 and 2017. We then conducted a set of literature searches to determine which of the 98 unique drugs we identified had shown efficacy in a rodent model of an AUD prior to being tested in a clinical trial.

RESULTS

We found that slightly less than half of the drugs tested in clinical trials (48%) had shown prior efficacy in any rodent model of an AUD, while the remaining 52% of drugs were used off-label, or in some cases, following non-published studies.

CONCLUSION

This study raises the question of how clinical researchers incorporate results from preclinical studies in the decision to bring a drug to a clinical trial. Our results underscore the need for ongoing communication among preclinical and clinical researchers.

CRF1 Receptor-Dependent Increases in Irritability-Like Behavior During Abstinence from Chronic Intermittent Ethanol Vapor Exposure

BACKGROUND

In humans, emotional and physical signs of withdrawal from ethanol are commonly seen. Many of these symptoms, including anxiety-like and depression-like behavior, have been characterized in animal models of ethanol dependence. One issue with several current behavioral tests that measure withdrawal in animal models is that they are often not repeatable within subjects over time. Additionally, irritability, one of the most common symptoms of ethanol withdrawal in humans, has not been well characterized in animal models. The corticotropin-releasing factor (CRF)-CRF₁ receptor system has been suggested to be critical for the emergence of anxiety-like behavior in ethanol dependence, but the role of this system in irritability-like behavior has not been characterized.

METHODS

The present study compared the effects of chronic intermittent ethanol (CIE) vapor exposure-induced ethanol dependence on irritability-like behavior in rats using the bottle-brush test during acute withdrawal and protracted abstinence. Rats were trained to self-administer ethanol in operant chambers and then either left in a nondependent state or made dependent via CIE. Naïve, nondependent, and dependent rats were tested for irritability-like behavior in the bottle-brush test 8 hours and 2 weeks into abstinence from ethanol. Separate cohorts of dependent and nondependent rats were used to examine the effect of the specific CRF₁ receptor antagonist R121919 on irritability-like behavior.

RESULTS

Dependent rats exhibited escalated ethanol intake compared with their own pre-CIE baseline and nondependent rats. At both time points of abstinence, ethanol-dependent rats exhibited increased aggressive-like responses compared with naïve and nondependent rats. R121919 reduced irritability-like behavior in both dependent and nondependent rats, but dependent rats were more sensitive to R121919.

CONCLUSIONS

Irritability-like behavior is a clinically relevant and reliable measure of negative emotional states that is partially mediated by activation of the CRF-CRF₁ system and remains elevated during protracted abstinence in ethanol-dependent rats.

Dexmedetomidine in the Treatment of Withdrawal Syndromes in Cardiothoracic Surgery Patients

Dexmedetomidine (Precedex, Abbott Laboratories, Abbott Park, IL) is an• 2adrenergic agonist that possesses a high ratio of specificity for the• 2versus the• 1receptor. It is currently approved for the provision of sedation during mechanical ventilation in adults. Given previous experience with clonidine for the treatment of substance withdrawal and the preliminary anecdotal experience with dexmedetomidine, it appears that dexmedetomidine may be a useful agent for treatment of substance withdrawal in the intensive care setting. The authors present their experience with the use of dexmedetomidine to control withdrawal behavior in 3 patients following cardiothoracic surgery. Previous reports regarding the use of dexmedetomidine to treat withdrawal and its potential application in this clinical arena are reviewed.

Dexmedetomidine for Alcohol Withdrawal Syndrome

OBJECTIVE

To review available evidence evaluating dexmedetomidine in alcohol withdrawal syndrome (AWS) while identifying gaps in evidence for its use in this setting.

DATA SOURCES

A MEDLINE search (1966-August 2015) to identify English-language articles evaluating the efficacy and safety of dexmedetomidine in alcohol withdrawal. Key words included alcohol, withdrawal, delirium tremens, and dexmedetomidine. Additional references were identified from a review of literature citations.

STUDY SELECTION AND DATA EXTRACTION

All English-language observational studies, retrospective reviews, and clinical trials were included. Case reports and case series describing the use of dexmedetomidine in 10 or fewer patients were excluded.

DATA SYNTHESIS

One randomized, controlled trial, 1 prospective observational study, and 6 retrospective reviews were identified. The only randomized, controlled trial identified showed that the addition of dexmedetomidine decreases benzodiazepine requirements more than placebo in the first 24 hours after initiation compared with the 24 hours prior to initiation (-56.8 mg vs -8 mg; P = 0.037). Overall, dexmedetomidine appears to lower benzodiazepine requirements in patients with AWS and decreases the sympathomimetic response seen in these patients. There was no convincing evidence that dexmedetomidine improves clinical endpoints in patients with AWS, such as need for mechanical ventilation or intensive care unit or hospital length of stay.

CONCLUSIONS

Dexmedetomidine reduces hypertension and tachycardia in AWS and also reduces benzodiazepine requirements; however, the impact of these findings on important clinical endpoints is yet to be determined. Dexmedetomidine may be useful as adjunctive therapy; however, it cannot be recommended as a single agent in the management of AWS.

Dexmedetomidine: a review of applications for cardiac surgery during perioperative period

Cardiac surgery is associated with a high incidence of cardiovascular and other complications during the perioperative period that translate into increased mortality and prolonged hospital stays. Safe comprehensive perioperative management is required to eliminate these adverse events. Dexmedetomidine is a selective α2-adrenoreceptor agonist that has been described as an ideal medication in the perioperative period of cardiac surgery. The major clinical effects of dexmedetomidine in this perioperative period can be summarized as attenuating the hemodynamic response, cardioprotective effects, antiarrhythmic effects, sedation in the ICU setting, treatment of delirium, and procedural sedation. Although there are some side effects of dexmedetomidine, it is emerging as an effective therapeutic agent in the management of a wide range of clinical conditions with an efficacious, safe profile. The present review serves as an overview update in the diverse applications of dexmedetomidine for cardiac surgery during the perioperative period.

Neurochemical mechanisms of alcohol withdrawal

Alcohol dependence encompasses a serious medical and societal problem that constitutes a major public health concern. A serious consequence of dependence is the emergence of symptoms associated with the alcohol withdrawal syndrome when drinking is abruptly terminated or substantially reduced. Clinical features of alcohol withdrawal include signs of central nervous system hyperexcitability, heightened autonomic nervous system activation, and a constellation of symptoms contributing to psychologic discomfort and negative affect. The development of alcohol dependence is a complex and dynamic process that ultimately reflects a maladaptive neurophysiologic state. Perturbations in a wide range of neurochemical systems, including glutamate, γ-aminobutyric acid, monoamines, a host of neuropeptide systems, and various ion channels produced by the chronic presence of alcohol ultimately compromise the functional integrity of the brain. These neuroadaptations not only underlie the emergence and expression of many alcohol withdrawal symptoms, but also contribute to enhanced relapse vulnerability as well as perpetuation of uncontrolled excessive drinking. This chapter highlights the hallmark features of the alcohol withdrawal syndrome, and describes neuroadaptations in a wide array of neurotransmitter and neuromodulator systems (amino acid and monoamine neurotransmitter, neuropeptide systems, and various ion channels) as they relate to the expression of various signs and symptoms of alcohol withdrawal, as well as their relationship to the significant clinical problem of relapse and uncontrolled dangerous drinking.

Dexmedetomidine for the treatment of alcohol withdrawal syndrome: rationale and current status of research

Dexmedetomidine is currently used in the US in the treatment of alcohol withdrawal syndrome (AWS) in the intensive care unit (ICU) setting, although data to support this practice are limited. Dexmedetomidine targets the noradrenergic system, an important but frequently overlooked secondary mechanism in the development of AWS, and, in doing so, may reduce the need for excessive benzodiazepine use which can increase the risk of γ-aminobutyric acid (GABA)-mediated deliriogenesis and respiratory depression. The purpose of this narrative review is to evaluate available literature reporting on the safety and efficacy of dexmedetomidine for AWS in the ICU setting. An English-language MEDLINE search (1966 to July 2013) was performed to identify articles evaluating the efficacy and safety of dexmedetomidine for AWS. Case series, case reports and controlled trials were evaluated for topic relevance and clinical applicability. Reference lists of articles retrieved through this search were reviewed to identify any relevant publications. Studies focusing on the safety and efficacy of dexmedetomidine for AWS in humans were selected. Studies were included if they were published as full articles; abstracts alone were not included in this review. Eight published case studies and case series were identified. Based on a limited body of evidence, dexmedetomidine shows promise as a potentially safe and possibly effective adjuvant treatment for AWS in the ICU. Prospective, well-controlled studies are needed to confirm the safety and efficacy of the use of dexmedetomidine in AWS.

Use of dexmedetomidine for the treatment of alcohol withdrawal syndrome in critically ill patients: a retrospective case series

Alcohol withdrawal syndrome (AWS) continues to be a challenge to manage in the ICU setting, and the ideal pharmacological treatment continues to evolve. Dexmedetomidine is a newer agent approved for short-term sedation in the ICU, but its use in the treatment of AWS has been limited. We report a retrospective case series of ten patients who were identified as receiving dexmedetomidine for AWS as designated by electronic pharmacy records. All subjects were male, with a mean age of 53.6 years, and a mean ICU length of stay of 9.3 days. They were all diagnosed with AWS by DSM-IV criteria. All the study patients received dexmedetomidine during their hospital course as a treatment for AWS. Studied variables included demographic data, dose and duration of dexmedetomidine, other pharmaceutical agents, and hemodynamics. Dexmedetomidine was safe to use in all patients, although mechanical ventilation was still required in three patients. With dexmedetomidine, the autonomic hyperactivity was blunted, with a mean 12.8% reduction in rate pressure product observed. Consideration should be given to the combined use of dexmedetomidine with benzodiazepines in the treatment of AWS.

Dexmedetomidine controls agitation and facilitates reliable, serial neurological examinations in a non-intubated patient with traumatic brain injury

INTRODUCTION

We report the effective use of dexmedetomidine in the treatment of a patient with a history of chronic alcohol abuse and an acute traumatic brain injury who developed agitation that was unresolved if from traumatic brain injury, or alcohol withdrawal or the combination of both. Treatment with benzodiazepines failed; lorazepam therapy obscured our ability to do reliable neurological testing to follow his brain injury and nearly resulted in intubation of the patient secondary to respiratory suppression. Upon admission to hospital, the patient was first treated with intermittent, prophylactic doses of lorazepam for potential alcohol withdrawal based upon our institution's standard of care. His neurological examinations including a motor score of 6 (obeying commands) on his Glasgow Coma Scale testing, laboratory studies, and repeat CT head imaging remained stable. For lack of published literature in diagnosing symptoms of patients with a history of both alcohol withdrawal and traumatic brain injury, a diagnosis of agitation secondary to presumed alcohol withdrawal was made when the patient developed acute onset of tachycardia, confusion, and extreme anxiety with tremor and attempts to climb out of bed requiring him to be restrained. Additional lorazepam doses were administered following a hospital-approved protocol for titration of benzodiazepine therapy for alcohol withdrawal. The patient's mental status and respiratory function deteriorated with the frequent lorazepam dosing needed to control his agitation. Dexmedetomidine IV infusion at a rate of 0.5 mcg/kg/h was then administered and was titrated ultimately to 1.5 mcg/kg/h. After 8 days of therapy with dexmedetomidine, the patient was transferred from the ICU to a step-down unit with an intact neurological examination and no evidence of alcohol withdrawal. Airway intubation was avoided during the patient's entire hospitalization. This case report highlights the intricate balance between the side effects of benzodiazepine sedation for treatment of agitation and the difficulties of monitoring the neurological status of non-intubated patients with traumatic brain injury.

CONCLUSION

Given the large numbers of alcohol-dependent patients who suffer a traumatic brain injury and subsequently develop agitation and alcohol withdrawal in hospital, dexmedetomidine offers a novel strategy to facilitate sedation without neurological or respiratory depression. As this case report demonstrates, dexmedetomidine is an emerging treatment option for agitation in patients who require reliable, serial neurological testing to monitor the course of their traumatic brain injury.

Dexmedetomidine: applications for the pediatric patient with congenital heart disease

This study aimed to provide a general description of the cardiovascular and hemodynamic effects of dexmedetomidine and an evidence-based review of the literature regarding its use in infants and children with congenital heart disease (CHD). A computerized bibliographic search of the literature on dexmedetomidine use in infants and children with CHD was performed. The cardiovascular effects of dexmedetomidine have been well studied in animal and adult human models. Adverse cardiovascular effects include occasional episodes of bradycardia, with rare reports of sinus pause or cardiac arrest. Both hypotension and hypertension also have been reported. The latter is related to peripheral α(2B) agonism leading to vasoconstriction. No adverse effects on the pulmonary vasculature have been noted even in patients with preexisting pulmonary hypertension. Although there are no direct effects on myocardial function, decreased cardiac output may result from changes in heart rate or increases in afterload. Although not currently Food and Drug Administration (FDA)-approved for the pediatric population, findings have shown dexmedetomidine to be effective in various clinical scenarios of patients with CHD including sedation during mechanical ventilation, prevention of procedure-related anxiety, prevention of emergence delirium and shivering after anesthesia, and treatment of withdrawal. Although dexmedetomidine may have limited utility for painful or invasive procedures, preliminary data suggest that the addition of ketamine to the regimen may offer benefits. When used during the perioperative period, additional benefits include blunting of the sympathetic stress response with a reduction of endogenous catecholamine release, a decrease in intraoperative anesthetic requirements, and a limitation of postoperative opioid requirements.

Tizanidine for alcohol withdrawal treatment

The noradrenergic system is an important neurotransmission system implicated in the occurrence of alcohol withdrawal symptoms and anxiety leading to relapse during abstinence from alcohol usage. Tizanidine can play a role in alcohol withdrawal since it interferes with the noradrenergic system neurotransmission. Many noradrenergic system inhibitors in the central nervous system have proven their efficacy in the treatment of alcohol withdrawal syndrome. Imidazoline receptors have been also implicated in the pathophysiology of addiction. Tizanidine is an α2-adrenoreceptor agonist that inhibits noradrenaline release and binds to imidazoline receptors. It is used as an antispastic agent due to its central action on noradrenergic system. Although Tizanidine has been tested as a treatment for opioid withdrawal it has not been tried in alcohol withdrawal yet. A theoretical rationale supports the fact that it can be an efficient treatment for the alcohol withdrawal syndrome as well as for the prevention of relapses.

Role of α2-agonists in the treatment of acute alcohol withdrawal

OBJECTIVE

To evaluate literature reporting on the role of norepinephrine in alcohol withdrawal and to determine the safety and efficacy of α(2)-agonists in reducing symptoms of this severe condition.

DATA SOURCES

Articles evaluating the efficacy and safety of the α(2)-agonists clonidine and dexmedetomidine were identified from an English-language MEDLINE search (1966-December 2010). Key words included alcohol withdrawal, delirium tremens, clonidine, dexmedetomidine, α(2)-agonist, norepinephrine, and sympathetic overdrive.

STUDY SELECTION AND DATA EXTRACTION

Studies that focused on the safety and efficacy of clonidine and dexmedetomidine in both animals and humans were selected.

DATA SYNTHESIS

The noradrenergic system, specifically sympathetic overdrive during alcohol withdrawal, may play an important role in withdrawal symptom development. Symptoms of sympathetic overdrive include anxiety, agitation, elevated blood pressure, tachycardia, and tremor. Therefore, α(2)-agonists, which decrease norepinephine release, may have a role in reducing alcohol withdrawal symptoms. The majority of controlled animal and human studies evaluated clonidine, but the most recent literature is from case reports on dexmedetomidine. The literature reviewed here demonstrate that these 2 α(2)-agonists safely and effectively reduce symptoms of sympathetic overdrive and concomitant medication use. Dexmedetomidine may offer an advantage over current sedative medications used in the intensive care unit, such as not requiring intubation with its use, and therefore further study is needed to fully elicit its benefit in alcohol withdrawal.

CONCLUSION

Clonidine and dexmedetomidine may provide additional benefit in managing alcohol withdrawal by offering a different mechanism of action for targeting withdrawal symptoms. Based on literature reviewed here, the primary role for clonidine and dexmedetomidine is as adjunctive treatment to benzodiazepines, the standard of care in alcohol withdrawal.

Dexmedetomidine infusion as adjunctive therapy to benzodiazepines for acute alcohol withdrawal

OBJECTIVE

To report a case of alcohol withdrawal and delirium tremens successfully treated with adjunctive dexmedetomidine.

CASE SUMMARY

A 30-year-old man with a history of alcohol abuse was admitted to the general medical unit because of altered mental status and agitation. He was initially treated for alcohol withdrawal with benzodiazepines; his condition then deteriorated and he was transferred to the intensive care unit. Because of the patient's poor response to benzodiazepines (oxazepam and lorazepam, with midazolam the last one used), intravenous dexmedetomidine was started at an initial dose of 0.2 microg/kg/h and titrated to 0.7 microg/kg/h to the patient's comfort. Midazolam was subsequently tapered to discontinuation due to excessive sedation. In the intensive care unit, the patient's symptoms remained controlled with use of dexmedetomidine alone. He remained in the intensive care unit for 40 hours; dexmedetomidine was then tapered to discontinuation and the patient was transferred back to the general medical unit on oral oxazepam and thiamine, which had been started in the emergency department. He was discharged after 5 days.

DISCUSSION

A review of the PubMed database (1989-2007) failed to identify any other instances of dexmedetomidine having been used as the principal agent to treat alcohol withdrawal. The use of sedative to treat delirium tremens is well documented, with benzodiazepines being the agents of choice. The clinical utility of benzodiazepines is limited by their stimulation of the gamma-aminobutyric acid receptors, an effect not shared by dexmedetomidine, a central alpha(2)-receptor agonist that induces a state of cooperative sedation and does not suppress respiratory drive.

CONCLUSIONS

In patients with delirium tremens, dexmedetomidine should be considered as an option for primary treatment. This case illustrates the need for further studies to investigate other potential uses for dexmedetomidine.

alpha1-noradrenergic receptor antagonism blocks dependence-induced increases in responding for ethanol

The purpose of this study was to test the hypothesis that blockade of alpha1-adrenergic receptors may suppress the excessive ethanol consumption associated with acute withdrawal in ethanol-dependent rats. Following the acquisition and stabilization of operant ethanol self-administration in male Wistar rats, dependence was induced in half the animals by subjecting them to a 4-week intermittent vapor exposure period in which animals were exposed to ethanol vapor for 14h/day. Subsequent to dependence induction, the effect of alpha1-noradrenergic receptor antagonist prazosin (0.0, 0.25, 0.5, 1, 1.5, and 2.0mg/kg IP) was tested on operant responding for ethanol in vapor-exposed and control rats during acute withdrawal. In ethanol-dependent animals, prazosin significantly suppressed responding at the 1.5 and 2.0mg/kg doses, whereas only the 2.0mg/kg dose was effective in nondependent animals, identifying an increase in the sensitivity to prazosin in dependent animals. Conversely, at the lowest dose tested (0.25mg/kg), prazosin increased responding in nondependent animals, which is consistent with the effect of anxiolytics on ethanol self-administration in nondependent animals. None of the doses tested reliably affected concurrent water self-administration. These results suggest the involvement of the noradrenergic system in the excessive alcohol drinking seen during acute withdrawal in ethanol-dependent rats.

Dexmedetomidine: applications in pediatric critical care and pediatric anesthesiology

OBJECTIVE

To provide a general descriptive account of the end-organ effects of dexmedetomidine and to provide an evidence-based review of the literature regarding its use in infants and children.

DATA SOURCE

A computerized bibliographic search of the literature regarding dexmedetomidine.

MAIN RESULTS

The end-organ effects of dexmedetomidine have been well studied in animal and adult human models. Adverse cardiovascular effects include occasional episodes of bradycardia with rare reports of sinus pause or cardiac arrest. Hypotension has also been reported as well as hypertension, the latter thought to be due to peripheral alpha2B agonism with peripheral vasoconstriction. Although dexmedetomidine has no direct effects on myocardial function, decreased cardiac output may result from changes in heart rate or increases in afterload. There are somewhat conflicting reports in the literature regarding its effects on ventilatory function, with some studies (both human and animal) suggesting a mild degree of respiratory depression, decreased minute ventilation, and decreased response to CO2 challenge whereas others demonstrate no effect. The central nervous system effects include sedation and analgesia with prevention of recall and memory at higher doses. Dexmedetomidine may also provide some neuroprotective activity during periods of ischemia. Applications in infants and children have included sedation during mechanical ventilation, prevention of emergence agitation following general anesthesia, provision of procedural sedation, and the prevention of withdrawal following the prolonged administration of opioids and benzodiazepines.

CONCLUSIONS

The literature contains reports of the use of dexmedetomidine in approximately 800 pediatric patients. Given its favorable sedative and anxiolytic properties combined with its limited effects on hemodynamic and respiratory function, there is growing interest in and reports of its use in the pediatric population in various clinical scenarios.

Nicotine stimulation on extracellular glutamate levels in the nucleus accumbens of ethanol-withdrawn rats in vivo

BACKGROUND

Nicotine can release glutamate in the limbic system. Presynaptic activation of glutamate receptors might be relevant for the subsequent firing of excitatory postsynaptic potentials. This might be relevant in early ethanol withdrawal. The effects and differences of nicotine stimulation on glutamate response measured by microdialysis in the nucleus accumbens (NAC) between ethanol-withdrawn rats (EW group) and ethanol-naïve rats (control group) were investigated.

METHODS

Rats were ethanol-intoxicated according to a binge-drinking model: recurrent cycle of 4 days of intoxication (EW group) or 5% sucrose (control group), followed by a 3-day recovery. This was followed by a 2-day intoxication period and subsequent abstinence. After the last oral intake, microdialysis was performed in the left NAC for a 16-hour withdrawal period. At the end of the withdrawal period, a rated withdrawal score (RWS) was documented. Then, nicotine was given subcutaneously at a dose of 0.5 mg/kg and amino acid levels determined by microdialysis were followed for an additional 3 hours.

RESULTS

The RWS was not correlated to the last amount of ethanol received, but was correlated to the total amount of ethanol administered during the pretreatment period: the basal values of extracellular glutamate were found to be decreased in the EW group before withdrawal. Cessation of ethanol significantly increased glutamate levels with a peak between 4 and 10 hours after the last oral intake. Sixteen hours after ethanol withdrawal, the same level as in the control group was achieved. Nicotine significantly increased glutamate levels in the NAC of the EW group but not in ethanol-naïve rats.

CONCLUSIONS

This study showed that withdrawal of ethanol was associated with an increase in extracellular glutamate levels. Systemic administration of nicotine in vivo produced an increase in extracellular levels of glutamate in the core region of the NAC during ethanol withdrawal. This might be a relevant pathomechanism for increased craving either for alcohol or for nicotine after ethanol withdrawal.

Periadolescent exposure to ethanol and diazepam alters the aversive properties of ethanol in adult mice

Evidence suggests that the developing adolescent brain may be especially vulnerable to long-term neurobehavioral consequences following ethanol exposure and withdrawal. In the present study, we examined the long-term effect of adolescent ethanol withdrawal on a subsequent EtOH-induced conditioned taste aversion (CTA). Periadolescent and adult C3H mice were exposed to 64 h of continuous (single withdrawal) or intermittent (multiple withdrawal) ethanol vapor. Following each ethanol exposure, animals received either 0, 1, 2, or 3 mg/kg diazepam (DZP) in an attempt to counteract the possible effect of ethanol withdrawal. About 6 weeks following ethanol and DZP treatment, animals were tested for an EtOH-induced CTA. As expected, exposure to EtOH during adolescence attenuated the EtOH-induced CTA as compared to controls. Unexpectedly, administration of DZP during withdrawal did not spare but rather mimicked the attenuation of the EtOH-induced CTA seen in animals exposed to ethanol in adolescence. This attenuation was not evident when EtOH and/or DZP was administered in adulthood. Given the similar mode of action of EtOH and DZP on the GABA system, the principal implication of the present findings is that the intoxicating effect of ethanol on the developing brain can result in long-term changes in the aversive properties of EtOH.

Diazepam during prior ethanol withdrawals does not alter seizure susceptibility during a subsequent withdrawal

The number of cycles of alcohol detoxification is suggested to be an important variable in the predisposition to severe withdrawal seizures in alcohol-dependent individuals. Several clinical studies have suggested that exposure to repeated alcohol withdrawals may lead to increased severity of subsequent withdrawal episodes. Consistent with these observations, exposure to multiple cycles of ethanol withdrawal in our previous study significantly increased sensitivity to the convulsive effects of the GABA(A) receptor inverse agonist, Ro15-4513, in comparison to continuous ethanol exposure with no intermittent withdrawals. There was also a selective increase in the occurrence of spontaneous spike and sharp wave (SSW) activity in the EEG recorded from hippocampal area CA(3) in proportion to the number of withdrawal episodes experienced. It is hypothesized that during such repeated episodes of ethanol intoxication and withdrawal, changes in neuronal excitation during prior withdrawals could serve as initially subconvulsive kindling stimuli that might eventually result in the increased severity of the withdrawal syndrome. There is some evidence of the successful suppression of such neuronal excitation during acute ethanol withdrawal by positive modulators of the GABA(A) receptor. In the present study, the benzodiazepine agonist, diazepam, at a dose (4.0 mg/kg) that suppresses acute withdrawal symptoms, when administered during intermittent withdrawals, did not alter seizure sensitivity during a subsequent nonmedicated withdrawal. Diazepam treatment during prior withdrawals also did not have any effect on the multiple withdrawal-associated increase in SSW activity in hippocampal area CA(3) during an untreated withdrawal. This finding suggests that suppression of acute withdrawal symptoms by diazepam does not prevent long-lasting changes in CNS function resulting from repeated exposures to ethanol withdrawal.