Ondansetron and opiate craving. A novel pharmacological approach to addiction

Trajectories of craving in the course of pharmacotherapy trials for methamphetamine use disorder

AIMS

The aim of this study was to measure trajectories of craving for methamphetamine during the course of pharmacotherapy trials for methamphetamine use disorder.

DESIGN, SETTING AND PARTICIPANTS

Craving trajectories were identified using Group-Based Trajectory Modeling. The association of craving trajectories with drug use trajectories was examined using a dual trajectory model. Association of craving trajectories with other health and social outcomes was also examined. The study used pooled data from five randomized controlled pharmacotherapy trials for methamphetamine use disorder. A total of 866 adults with methamphetamine use disorder participated in randomized controlled pharmacotherapy trials.

MEASUREMENT

Craving was assessed weekly using the Brief Substance Craving Scale. Drug use was assessed using urine toxicology. Alcohol- and drug-related problems, as well as psychiatric, medical, legal, employment and relationship problems, were measured using the Addiction Severity Index.

FINDINGS

A three-trajectory model with high, medium and low craving trajectories was selected as the most parsimonious model. Craving trajectories were associated with methamphetamine use trajectories in the course of trial; 88.4% of those in the high craving trajectory group had a consistently high frequency of methamphetamine use compared with 18.7% of those in the low craving group. High craving was also associated with less improvement in most other outcomes and higher rate of dropout from treatment. In turn, low craving was associated with a rapidly decreasing frequency of methamphetamine use, greater improvement in most other outcomes and a lower rate of dropout. Participants on modafinil daily and ondansetron 1 mg twice daily were less likely to be in the high craving group compared with those on placebo.

CONCLUSIONS

Trajectories of methamphetamine craving in the course of clinical trials for methamphetamine use disorder appear to be both highly variable and strongly associated with greater frequency of drug use, other drug-related outcomes and dropout from trials. Two medications, modafinil daily and ondansetron at a dose of 1 mg two times daily, appear to be associated with greater reduction in craving in the course of treatment compared with placebo. A decrease in methamphetamine craving shows promise as an early indicator of recovery from methamphetamine use disorder.

Recent advances with 5-HT3 modulators for neuropsychiatric and gastrointestinal disorders

Serotonin (5-hydroxytryptophan [5-HT]) is a biologically active amine expressed in platelets, in gastrointestinal (GI) cells and, to a lesser extent, in the central nervous system (CNS). This biogenic compound acts through the activation of seven 5-HT receptors (5-HT_1-7 Rs). The 5-HT₃ R is a ligand-gated ion channel belonging to the Cys-loop receptor family. There is a wide variety of 5-HT₃ R modulators, but only receptor antagonists (known as setrons) have been used clinically for chemotherapy-induced nausea and vomiting and irritable bowel syndrome treatment. However, since the discovery of the setrons in the mid-1980s, a large number of studies have been published exploring new potential applications due their potency in the CNS and mild side effects. The results of these studies have revealed new potential applications, including the treatment of neuropsychiatric disorders such as schizophrenia, depression, anxiety, and drug abuse. In this review, we provide information related to therapeutic potential of 5-HT₃ R antagonists on GI and neuropsychiatric disorders. The major attention is paid to the structure, function, and pharmacology of novel 5-HT₃ R modulators developed over the past 10 years.

5-HT3 Receptor Antagonists in Neurologic and Neuropsychiatric Disorders: The Iceberg Still Lies beneath the Surface

5-HT₃ receptor antagonists, first introduced to the market in the mid-1980s, are proven efficient agents to counteract chemotherapy-induced emesis. Nonetheless, recent investigations have shed light on unappreciated dimensions of this class of compounds in conditions with an immunoinflammatory component as well as in neurologic and psychiatric disorders. The promising findings from multiple studies have unveiled several beneficial effects of these compounds in multiple sclerosis, stroke, Alzheimer disease, and Parkinson disease. Reports continue to uncover important roles for 5-HT₃ receptors in the physiopathology of neuropsychiatric disorders, including depression, anxiety, drug abuse, and schizophrenia. This review addresses the potential of 5-HT₃ receptor antagonists in neurology- and neuropsychiatry-related disorders. The broad therapeutic window and high compliance observed with these agents position them as suitable prototypes for the development of novel pharmacotherapeutics with higher efficacy and fewer adverse effects.

Pharmacological means of reducing human drug dependence: a selective and narrative review of the clinical literature

Substance abuse or addictive disorder is a global problem. A greater understanding of the associated changes in brain pathophysiology supports the notion that pharmacological treatments are part of the necessary treatment options. Craving is a core symptom of addictive disorder. It refers to a strong desire to use drugs again either to re-experience positive effects or to diminish negative experiences. Currently there are a number of medicines that are effective in the treatment of addictive disorders. These medications can either be for substitution (same pharmacological effect as the abused substance) or anticraving (decrease the craving of the abused substance). In this MEDLNE based review, specific compounds (naltrexone, acamprosate, topiramate, disulfiram, baclofen, N-acetylcysteine and bupropion) were selected that are known to diminish desire to use (anticraving effect) and that have been trialled for a number of different substance addictive disorders. Their therapeutic potential in clinical practice is discussed in light of their efficacy.

A pilot study of full-dose ondansetron to treat heavy-drinking men withdrawing from alcohol in Brazil

Ondansetron has emerged as a promising medication for the treatment of alcohol dependence, mainly among early-onset alcoholics. This research primarily aimed to evaluate the efficacy and safety of ondansetron at a 16mg/day dosage to treat alcohol-dependent outpatients. A double-blind, placebo-controlled, 12-week study was carried out at the University of São Paulo, Brazil. The total sample comprised 102 men, 18-60 years of age, with an International Classification of Diseases (ICD-10) diagnosis of alcohol dependence. Half of our sample discontinued the treatment and the main outcome measures (proportion of abstinent days and proportion of heavy drinking days) were analyzed using the treatment adherents as well as with an imputed sample. The main factors associated with treatment retention were older age and smoking status. Although there were no significant differences between the main outcome measures of both medication groups in the adherents, ondansetron demonstrated a slight but significant superiority over the placebo regarding the proportion of heavy drinking days in the imputed sample (7.8% versus 11.7%, respectively). It appears that the optimal dosage to treat alcoholism has yet to be determined. Further, ondansetron may only be useful in treating some types of alcoholics. Ondansetron was well tolerated and no serious adverse events were registered.

Alleviating symptoms of withdrawal from an opioid

INTRODUCTION

Patients who are discharged following surgery on an oral opioid, and who have taken the drug for 2 or more weeks often experience withdrawal symptoms when they try to discontinue the drug.

CASE REPORT

Three weeks after discharge, a 44-year-old female patient decided to reduce her oxycodone (OxyContin(®)) dosage from 20 mg three times a day to 20 mg two times a day. She experienced severe withdrawal symptoms.

METHOD

To assist her in withdrawing from the remainder of the drug, a protocol using ondansetron was developed.

RESULTS

After 10 days, the patient was opioid and withdrawal-symptom free.

CONCLUSION

Use of ondansetron along with tapering of the opioid was safe and effective in preventing further withdrawal symptoms. This case should stimulate research with a larger, more diverse population including those with both short-term and chronic opioid dependence.

The auspicious role of the 5-HT3 receptor in depression: a probable neuronal target?

The serotonergic mechanisms have been successfully utilized by the majority of antidepressant drug discovery programmes, while the search for newer targets remains persistent. The present review focused on the serotonin type-3 receptor, the only ion channel subtype in the serotonin family. Behavioural, neurochemical, electrophysiological and molecular analyses, including the results from our laboratory, provided substantial evidence that rationalizes the correlation between serotonin type-3 receptor modulation and rodent depressive-like behaviour. Nevertheless, the reports on polymorphism of serotonin type-3 receptor genes and data from clinical studies (on serotonin type-3 receptor antagonists) were insufficient to corroborate the involvement of this receptor in the neurobiology of depression. The preclinical and clinical studies that have contradicted the antidepressant-like effects of serotonin type-3 receptor antagonists and the reasons underlying such disagreement were discussed. Finally, this critical review commended the serotonin type-3 receptor as a candidate neuronal antidepressant drug target.

Precipitated and conditioned withdrawal in morphine-treated rats

RATIONALE

Stimuli that are paired with opioid withdrawal can themselves produce effects similar to withdrawal that might promote relapse.

OBJECTIVE

This study compared precipitated and conditioned withdrawal and tested whether withdrawal is modified by clonidine or morphine.

METHODS

Morphine-treated rats (10 mg/kg/12 h) received naloxone (3.2 mg/kg) in a novel environment (conditioned stimuli [CS]). Other rats received naloxone in the absence of the CS. Body weight and observable signs were used to measure withdrawal.

RESULTS

Naloxone produced weight loss and withdrawal signs in morphine-treated rats. Following pairings of the CS and naloxone, the CS alone had effects similar to naloxone; conditioned withdrawal was greater after three naloxone/CS pairings, as compared to one, and with longer morphine treatment. Antagonist-precipitated withdrawal was greater in rats that previously were physically dependent on morphine, as compared to withdrawal in rats that were never dependent; however, conditioned withdrawal did not differ between groups. When administered concurrently with naloxone, clonidine (0.1 mg/kg) attenuated some precipitated withdrawal signs, although conditioned withdrawal was largely unchanged. Administration of 10 mg/kg of morphine before the CS alone attenuated all conditioned withdrawal signs, whereas 0.1 mg/kg of clonidine before the CS alone reduced some directly observable signs and not weight loss.

CONCLUSIONS

Conditioned withdrawal occurs rapidly and is greater with longer periods of morphine treatment or more pairings of naloxone and the CS; however, a history of physical dependence does not increase conditioned withdrawal. Modification of conditioned withdrawal by drugs might be a useful approach for treating relapse.

From mouse to man: the 5-HT3 receptor modulates physical dependence on opioid narcotics

OBJECTIVES

Addiction to opioid narcotics represents a major public health challenge. Animal models of one component of addiction, physical dependence, show this trait to be highly heritable. The analysis of opioid dependence using contemporary in-silico techniques offers an approach to discover novel treatments for dependence and addiction.

METHODS

In these experiments, opioid withdrawal behavior in 18 inbred strains of mice was assessed. Mice were treated for 4 days with escalating doses of morphine before the administration of naloxone allowing the quantification of opioid dependence. After haplotypic analysis, experiments were designed to evaluate the top gene candidate as a modulator of physical dependence. Behavioral studies as well as measurements of gene expression on the mRNA and protein levels were completed. Finally, a human model of opioid dependence was used to quantify the effects of the 5-HT3 antagonist ondansetron on signs and symptoms of withdrawal.

RESULTS

The Htr3a gene corresponding to the 5-HT3 receptor emerged as the leading candidate. Pharmacological studies using the selective 5-HT3 antagonist ondansetron supported the link in mice. Morphine strongly regulated the expression of the Htr3a gene in various central nervous system regions including the amygdala, dorsal raphe, and periaqueductal gray nuclei, which have been linked to opioid dependence in previous studies. Using an acute morphine administration model, the role of 5-HT3 in controlling the objective signs of withdrawal in humans was confirmed.

CONCLUSION

These studies show the power of in-silico genetic mapping, and reveal a novel target for treating an important component of opioid addiction.

The role of 5-HT3 receptors in drug abuse and as a target for pharmacotherapy

Alcohol and drug abuse continue to be a major public health problem in the United States and other industrialized nations. Extensive preclinical research indicates the mesolimbic dopamine (DA) pathway and associated regions mediate the rewarding and reinforcing effects of drugs of abuse and natural rewards, such as food and sex. The serotonergic (5-HT) system, in concert with others neurotransmitter systems, plays a key role in modulating neuronal systems within the mesolimbic pathway. A substantial portion of this modulation is mediated by activity at the 5-HT3 receptor. The 5-HT3 receptor is unique among the 5-HT receptors in that it directly gates an ion channel inducing rapid depolarization that, in turn, causes the release of neurotransmitters and/or peptides. Preclinical findings indicate that antagonism of the 5-HT3 receptor in the ventral tegmental area, nucleus accumbens or amygdala reduces alcohol self-administration and/or alcohol-associated effects. Less is known about the effects of 5-HT3 receptor activity on the self-administration of other drugs of abuse or their associated effects. Clinical findings parallel the preclinical findings such that antagonism of the 5-HT3 receptor reduces alcohol consumption and some of its subjective effects. This review provides an overview of the structure, function, and pharmacology of 5-HT3 receptors, the role of these receptors in regulating DA neurotransmission in mesolimbic brain areas, and discusses data from animal and human studies implicating 5-HT3 receptors as targets for the development of new pharmacological agents to treat addictions.

Neural responses associated with cue evoked emotional states and heroin in opiate addicts

Ten male opiate addicts, who were current heroin injectors, underwent positron emission tomographic (PET) scanning during exposure to a sequence of six alternating drug related and neutral video cues, on two occasions. After the second scan, each subject received heroin or placebo using a randomised single-blind procedure. This design allowed the investigation of patterns of brain activity during a range of self-reported cue evoked emotional states, both in the presence and absence of heroin. Self-reports of 'urge to use' correlated strongly with increased regional blood flow (rCBF) in the inferior frontal and orbitofrontal cortex target regions of the mesolimbic dopaminergic system, implicated in conditioning and reward. 'Urge to use' was also associated with highly significant increased rCBF in the right pre-cuneus, an area associated with episodic memory retrieval, and in the left insula, implicated in the processing of the emotional components of stimuli. Self-reports of feeling 'high' correlated with rCBF activation in the hippocampus, an area relevant to the acquisition of stimulus-associated reinforcement.

Activation of reward circuitry in human opiate addicts

The neurobiological mechanisms of opiate addictive behaviour in humans are unknown. A proposed model of addiction implicates ascending brainstem neuromodulatory systems, particularly dopamine. Using functional neuroimaging, we assessed the neural response to heroin and heroin-related cues in established opiate addicts. We show that the effect of both heroin and heroin-related visual cues are maximally expressed in the sites of origin of ascending midbrain neuromodulatory systems. These context-specific midbrain activations predict responses to salient visual cues in cortical and subcortical regions implicated in reward-related behaviour. These findings implicate common neurobiological processes underlying drug and drug-cue-related effects.

Novel antipsychotic medications and the treatment of comorbid substance abuse in schizophrenia

Comorbid substance abuse (SA) in schizophrenia is a significant problem. Moreover, these patients are particularly difficult to treat. This report reviews the pharmacological management of comorbid SA and schizophrenia and a case report is provided to illustrate the potential of novel antipsychotic medications.

Effects of ondansetron administration on opioid withdrawal syndrome observed in rats

This study tested whether a 5-HT3 receptor antagonist could reverse the signs of precipitated opioid withdrawal. Rats were treated with either saline or morphine for 4 days. After the four days, half of the rats in each group received naloxone and half received saline. Each animal also received one of four doses of ondansetron (0, 1, 2 and 4 mg/kg i.p.). Administration of ondansetron to rats receiving naloxone after chronic morphine decreased the intensity of withdrawal signs such as increased defecation, jumping and wet-dog shakes, elevated the nociceptive threshold values which were decreased by precipitated withdrawal, but produced no change in urination, rectal temperature or salivation. The effects exhibited by ondansetron administration may be explained through interference of its 5-HT3 receptor antagonist activity with serotoninergic mechanisms involved in the regulation of these withdrawal symptoms. The use of this drug is thus suggested as a possible treatment of opioid withdrawal signs in heroin addicts.

Imagery of craving in opiate addicts undergoing detoxification

Craving is a significant factor in opiate addiction that is associated with drug-dependence and in relapse to drug use after treatment. In order to better understand the psychological and physiological mechanisms of craving for opiates, we have developed an imagery-based procedure using personal verbal descriptions of craving in abstinent opiate addicts. Thirteen opiate addicts in detoxification were required to imagine and describe their craving experiences while autonomic measures of heart rate and arterial pressure were taken. Subjects displayed a significant increase in systolic blood pressure and heart rate while describing drug craving compared with neutral descriptions. Furthermore, an increase in systolic blood pressure during imagery of craving descriptions compared with neutral descriptions was observed. These results provide preliminary evidence that imagery is powerful in eliciting craving for opiates, as indicated by subjective ratings and autonomic measures. The implications of the results of this paper for the cue-exposure paradigm and contemporary models of addiction are being discussed.