Guidelines and methodological reviews concerning drug abuse liability assessment

Cebranopadol, a novel long-acting opioid agonist with low abuse liability, to treat opioid use disorder: Preclinical evidence of efficacy

Maintenance therapy with buprenorphine and methadone is the gold standard pharmacological treatment for opioid use disorder (OUD). Despite these compounds demonstrating substantial efficacy, a significant number of patients do not show optimal therapeutic responses. The abuse liability of these medications is also a concern. Here we used rats to explore the therapeutic potential of the new long-acting pan-opioid agonist Cebranopadol in OUD. We tested the effect of cebranopadol on heroin self-administration and yohimbine-induced reinstatement of heroin seeking. In addition, we evaluated the abuse liability potential of cebranopadol in comparison to that of heroin under fixed ratio 1 (FR1) and progressive ratio (PR) operant self-administration contingencies. Oral administration of cebranopadol (0, 25, 50 μg/kg) significantly attenuated drug self-administration independent of heroin dose (1, 7, 20, 60μg/inf). Cebranopadol also reduced the break point for heroin (20 μg/inf). Finally, pretreatment with cebranopadol significantly attenuated yohimbine-induced reinstatement of drug seeking. In abuse liability experiments under FR1 contingency, rats maintained responding for heroin (1, 7, 20, 60μg/inf) to a larger extent than cebranopadol (0.03, 0.1, 0.3, 1.0, 6.0μg/inf). Under PR contingency, heroin maintained responding at high levels at all except the lowest dose, while the break point (BP) for cebranopadol did not differ from that of saline. Together, these data indicate that cebranopadol is highly efficacious in attenuating opioid self-administration and stress-induced reinstatement, while having limited abuse liability properties. Overall, the data suggest clinical potential of this compound for OUD treatment.

High Interest in Injectable Opioid Agonist Treatment With Hydromorphone Among Urban Syringe Service Program Participants

BACKGROUND

Injectable opioid agonist treatment with hydromorphone (iOAT-H) is effective for persons who inject drugs (PWID) with opioid use disorder (OUD) but remains unavailable in the United States. Our objective was to determine interest in iOAT-H among syringe services program (SSP) participants.

METHODS

We recruited PWID with OUD from SSPs in New York City. Interest in iOAT-H was assessed on a 4-point scale. We compared participants who were and were not interested in iOAT-H regarding sociodemographic characteristics and self-reported variables (past 30 days): heroin use, public injection practices, and participation in illegal activity other than drug possession. Participants reported their preferred OUD treatment and reasons for these preferences.

RESULTS

Of 108 participants, most were male (69%), Hispanic (68%), and median age was 42 years. The median number of prior OUD treatment episodes was 6 (interquartile range: 2-12). Most (65%) were interested in iOAT-H. Interested participants (vs not interested) reported, over the prior 30 days, greater heroin use days (mean, 26.4 vs 22.3), injecting in public more times (median, 15 vs 6), and a higher percentage having participated in illegal activity (40% vs 16%). Preferences for OUD treatment were: iOAT-H (43%), methadone (39%), and buprenorphine (9%). Participants who preferred iOAT-H to conventional OUD treatments reported preferring injection as a route of administration and that available OUD treatments helped them insufficiently.

CONCLUSIONS

SSP participants with OUD reported high interest in iOAT-H. Participants had attempted conventional treatments but still used heroin almost daily. We identified PWID at risk for opioid-related harms who potentially could benefit from iOAT-H.

Cebranopadol, a novel long-acting opioid agonist with low abuse liability, to treat opioid use disorder: Preclinical evidence of efficacy

The gold standard pharmacological treatment for opioid use disorder (OUD) consists of maintenance therapy with long-acting opioid agonists such as buprenorphine and methadone. Despite these compounds having demonstrated substantial efficacy, a significant number of patients do not show optimal therapeutic responses. Moreover, the abuse liability of these medications remains a major concern. Cebranopadol, is a new, long-acting pan-opioid agonist that also activates the nociception/orphanin FQ NOP receptor. Here we used rats to explore the therapeutic potential of this agent in OUD. First, in operant intravenous self-administration experiments we compared the potential abuse liability of cebranopadol with the prototypical opioid heroin. Under a fixed ratio 1 (FR1) contingency, rats maintained responding for heroin (1, 7, 20, 60 μg/inf) to a larger extent than cebranopadol (0.03, 0.1, 0.3, 1.0, 6.0 μg/inf). When the contingency was switched to a progressive ratio (PR) reinforcement schedule, heroin maintained responding at high levels at all except the lowest dose. Conversely, in the cebranopadol groups responding decreased drastically and the break point (BP) did not differ from saline controls. Next, we demonstrated that oral administration of cebranopadol (0, 25, 50 μg/kg) significantly attenuated drug self-administration independent of heroin dose (1, 7, 20, 60 μg/inf). Cebranopadol also reduced the break point for heroin (20 μg/inf). Furthermore, in a heroin self-administration training extinction/reinstatement paradigm, pretreatment with cebranopadol significantly attenuated yohimbine stress-induced reinstatement of drug seeking. Together, these data indicate that cebranopadol has limited abuse liability compared to heroin and is highly efficacious in attenuating opioid self-administration and stress-induced reinstatement, suggesting clinical potential of this compound for OUD treatment.

Kava (Piper methysticum) in the United States: the quiet rise of a substance with often subtle effects

Background: Piper methysticum, commonly called kava, has long been consumed in beverage form in the Pacific Islands. Kava use in the US has slowly increased since the 1990s, but is not assessed in major epidemiological surveys.Objectives: To analyze social-media posts about kava from current, past, and prospective users, for motivations, patterns of co-use, and effects.Methods: Text from Reddit posts, and accompanying metadata, were collected and thematically coded by two independent raters.Results: 423 posts were collected, spanning January 2006 through December 2021. Of the 1,211 thematic codes applied, 1,098 (90. 7%) were concordant. Motivations for use bifurcated into self-treatment (for psychiatric or physical health conditions) and recreation; these were not mutually exclusive. Kava was rarely considered strongly euphoriant, but was valued as an anxiolytic. Kava was frequently used with other substances, most commonly kratom. Kava was used at lower doses for self-treatment than for other purposes (pseudo-R² = 0.11). Undesirable effects (gastrointestinal upset, fatigue) were mentioned, though less often than benefits. Hepatotoxicity, reported elsewhere as a rare, non-dose-related risk, was disputed on the basis of its not having been experienced by those posting.Conclusion: Kava appears to be conceptualized among Reddit posters as an anxiolytic with few risks or adverse effects. As it grows in popularity, especially among people who use other drugs that are more liable to misuse or addiction, it should be assessed in probability samples (i.e. in the major national drug surveys) and clinical practice for its risks, potential benefits, and possible drug-drug interactions.

Subjective responses predict d-amphetamine choice in healthy volunteers

BACKGROUND

It is commonly believed that drugs, including stimulants, are used recreationally because of their ability to induce pleasurable subjective effects. However, recreational drug use sometimes occurs in the absence of positive subjective effects, suggesting that other factors contribute. Here, we examine the extent to which the direct subjective effects of amphetamine, a commonly misused stimulant, predict subsequent choice of the drug vs placebo.

METHODS

Healthy adults (N = 112) participated in a five-session amphetamine choice study. On the first four sessions, participants sampled either 20 mg d-amphetamine or placebo in color-coded capsules two times each. On the fifth session, they chose which color (d-amphetamine or placebo) they preferred. We examined the choice of drug vs placebo in relation to demographic characteristics, baseline mood states, personality and subjective and cardiovascular responses to acute administration of the drug.

RESULTS

Eighty-one participants chose amphetamine (Choosers) while 31 chose placebo (Non-choosers). Overall, amphetamine produced typical stimulant-like effects on subjective questionnaires, and it elevated heart rate and blood pressure vs placebo. Choosers reported greater positive mood, elation and stimulant-like effects following amphetamine compared to Non-choosers. The Choosers also exhibited a greater increase in systolic blood pressure, but not heart rate. The groups did not differ on demographic characteristics, mood states before drug administration or personality.

CONCLUSIONS

These findings support the idea that pleasurable subjective responses to amphetamine, including positive mood, elation, and stimulant-like effects influence behavioral choice of the drug.

Hippocampal-Dependent Inhibitory Learning and Memory Processes in the Control of Eating and Drug Taking

As manifestations of excessive and uncontrolled intake, obesity and drug addiction have generated much research aimed at identifying common neuroadaptations that could underlie both disorders. Much work has focused on changes in brain reward and motivational circuitry that can overexcite eating and drug-taking behaviors. We suggest that the regulation of both behaviors depends on balancing excitation produced by stimuli associated with food and drug rewards with the behavioral inhibition produced by physiological "satiety" and other stimuli that signal when those rewards are unavailable. Our main hypothesis is that dysregulated eating and drug use are consequences of diet- and drug-induced degradations in this inhibitory power. We first outline a learning and memory mechanism that could underlie the inhibition of both food and drug-intake, and we describe data that identifies the hippocampus as a brain substrate for this mechanism. We then present evidence that obesitypromoting western diets (WD) impair the operation of this process and generate pathophysiologies that disrupt hippocampal functioning. Next, we present parallel evidence that drugs of abuse also impair this same learning and memory process and generate similar hippocampal pathophysiologies. We also describe recent findings that prior WD intake elevates drug self-administration, and the implications of using drugs (i.e., glucagon-like peptide- 1 agonists) that enhance hippocampal functioning to treat both obesity and addiction are also considered. We conclude with a description of how both WD and drugs of abuse could initiate a "vicious-cycle" of hippocampal pathophysiology and impaired hippocampal-dependent behavioral inhibition.

No Abuse Potential of Silexan in Healthy Recreational Drug Users: A Randomized Controlled Trial

BACKGROUND

Silexan is a lavender essential oil with established anxiolytic and calming efficacy. Here we asked whether there is a potential for abuse in human patients.

METHODS

We carried out a phase I abuse liability single-center, double-blind, 5-way crossover study in healthy users of recreational central nervous system depressants. They received single oral doses of 80 mg (therapeutic dose) and 640 mg Silexan, 2 mg and 4 mg lorazepam (active control) and placebo in randomized order, with 4- to 14-day washout periods between treatments. Pharmacodynamic measures included validated visual analogue scales assessing positive, negative, and sedative drug effects and balance of effects; a short form of the Addiction Research Center Inventory; and a drug similarity assessment. The primary outcome measure was the individual maximum value on the drug liking visual analogue scale during 24 hours post-dose.

RESULTS

Forty participants were randomized and 34 were evaluable for pharmacodynamic outcomes. In intraindividual head-to-head comparisons of the drug liking visual analogue scale maximum value, both doses of Silexan were rated similar to placebo whereas differences were observed between Silexan and lorazepam and between placebo and lorazepam (P < .001). These data were supported by all secondary measures of positive drug effects and of balance of effects. Differences between placebo and both doses of Silexan were always negligible in magnitude. Moreover, Silexan showed no sedative effects and was not perceived to be similar to commonly used drugs that participants had used in the past.

CONCLUSIONS

Silexan did not exhibit any abuse potential in a standard abuse potential detection screen study and is unlikely to be recreationally abused.

Subjective Effects of Alcohol Predict Alcohol Choice in Social Drinkers

INTRODUCTION

Alcohol is among the most commonly used psychoactive drugs, yet it can produce markedly different subjective effects in different people. Certain effects, including both heightened stimulatory effects and lesser sedative effects, are thought to predict repeated or excessive use. However, we do not fully understand the nature of these individual differences or their relationships to alcohol consumption. This controlled laboratory study examined subjective and physiologic responses to a moderate dose of alcohol in social drinkers in relation to the subjects' decision to consume alcohol.

METHODS

Healthy adult volunteers (N = 95) participated in a 5-session double-blind alcohol choice study. On the first 4 sessions, they received alcohol (0.8 g/kg) and placebo in alternating order, and on the fifth session, they chose and consumed whichever of the 2 they preferred. During each session, participants completed the Profile of Mood States (POMS) and Biphasic Alcohol Effects Scale (BAES) questionnaires and had their vitals recorded every 30 minutes. We compared subjective and physiologic response to alcohol during the sampling sessions in participants who chose alcohol or placebo on session 5.

RESULTS

Of the 95 participants, 55 chose alcohol (choosers) and 40 chose placebo (nonchoosers). In the full sample, alcohol produced its expected effects (e.g., increased friendliness, elation, and vigor (POMS), and stimulation and sedation (BAES)). The chooser and nonchooser groups did not differ in demographic characteristics, blood alcohol levels, or cardiovascular measures. However, the choosers experienced greater alcohol-induced increases in positive mood (POMS) and liked the drug more, whereas the nonchoosers experienced greater anger, anxiety (POMS), and sedation (BAES) after alcohol.

CONCLUSION

Both greater positive mood effects and lesser sedative effects after alcohol predicted preference under controlled conditions, suggesting that both factors can predict future consumption of alcohol.

Randomized Crossover Trial to Compare Abuse Liability of Intravenous Remimazolam Versus Intravenous Midazolam and Placebo in Recreational Central Nervous System Depressant Users

Remimazolam (RMZ) is a new and ultra-fast-acting, short-duration intravenous benzodiazepine, a drug class associated with abuse potential. This trial was designed to compare the abuse potential of remimazolam with placebo and midazolam (MDZ), a well-characterized member of the same pharmacological class in healthy, recreational drug users 18-55 years-of-age, who demonstrated good drug tolerance and were able to discriminate between midazolam and placebo. At equipotent intravenous doses selected to produce effects ranging from mild/moderate to relatively strong sedation without loss of consciousness (RMZ: 5, 10 mg versus MDZ: 2.5, 5 mg), peak scores (E_max or E_min , respectively) for drug liking, good/bad/any effects, and sedation (drowsiness and relaxation) were significantly greater than placebo for both active drugs and were broadly comparable between RMZ and MDZ. In contrast, areas under the effect-time curves (TA_AUE) were notably lower for RMZ versus MDZ, particularly for measures of good and any effects, reflecting the shorter duration of action and consistent with the more rapid observed plasma clearance for RMZ versus MDZ and the lack of an active RMZ metabolite. Scores for willingness to take drug again were also lower for RMZ versus MDZ, but not significantly so. We concluded that the abuse potential of RMZ is comparable to or lower than that of MDZ, a drug known to have a low potential for intravenous abuse.

Abuse liability of electronic cigarettes in men who are experienced electronic cigarette users

Most electronic cigarettes (e-cigs) aerosolize a nicotine-containing liquid that users inhale. Few experimental studies have examined e-cig abuse liability (the extent to which use of these products may lead to persistent and/or problematic use). In this study, 24 experienced male e-cig users completed 4 sessions that differed byproduct used: own e-cig (OWN), an eGo e-cig filled with participants' own brand/flavor liquid in 0 mg/mL nicotine (e-cig0), an eGo e-cig filled with the highest nicotine concentration available in participants' own brand/flavor (e-cighighest), and a U.S. Food and Drug Administration-approved nicotine inhaler (IN). Outcome measures included crossover point on the multiple-choice procedure, plasma nicotine delivery, and subjective effect profile. After 10 puffs, a significantly higher mean crossover point was observed for OWN at $1.35 (SD = 0.90) compared to e-cighighest at $0.88 (SD = 0.89), e-cig0 at $0.83 (SD = 0.79), and IN at $0.72 (SD = 0.84). Significant increases in mean plasma nicotine concentration were observed for OWN at 7.94 ng/mL (SD = 6.19) and e-cighighest at 7.51 ng/mL (SD = 5.39). Significant reductions in abstinence symptom suppression and higher ratings of satisfaction were observed for OWN and e-cighighest, with significantly less suppression and lower ratings of satisfaction for e-cig0 and IN. These findings suggest that human laboratory methods can be used to assess e-cig abuse liability and that nicotine-containing e-cigs have greater abuse liability than nicotine-free e-cigs and the IN. Potential regulations intended to limit e-cig abuse liability should be tested using these or similar procedures. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Lack of correlation between the activity of the mesolimbic dopaminergic system and the rewarding properties of pregabalin in mouse

RATIONALE

Pregabalin is a psychoactive drug indicated in the treatment of epilepsy, neuropathic pain, and generalized anxiety disorders. Pregabalin acts on different neurotransmission systems by inactivating the alpha2-delta subunit of voltage-gated calcium channels. In light of this pharmacological property, the hypothesis has been raised that pregabalin may regulate the mesolimbic dopamine pathway and thereby display a potential for misuse or abuse as recently observed in humans. Although some preclinical data support this possibility, the rewarding properties of gabapentinoid are still a matter for debate.

OBJECTIVE

The aim of this work was to evaluate the rewarding properties of pregabalin and to determine its putative mechanism of action in healthy mice.

RESULTS

Pregabalin alone (60 mg/kg; s.c.) produced a rewarding effect in the conditioned place preference (CPP) test albeit to a lower extent than cocaine (30 mg/kg; s.c.). Interestingly, when assessing locomotor activity in the CPP, the PGB60 group, similarly to the cocaine group, showed an increased locomotor activity. In vivo single unit extracellular recording showed that pregabalin had mixed effects on dopamine (DA) neuronal activity in the ventral tegmental area since it decreased the activity of 50% of neurons and increased 28.5% of them. In contrast, cocaine decreased 75% of VTA DA neuronal activity whereas none of the neurons were activated. Intracerebal microdialysis was then conducted in awake freely mice to determine to what extent such electrophysiological parameters influence the extracellular DA concentrations ([DA]ext) in the nucleus accumbens. Although pregabalin failed to modify this parameter, cocaine produced a robust increase (800%) in [DA]ext.

CONCLUSIONS

Collectively, these electrophysiological and neurochemical experiments suggest that the rewarding properties of pregabalin result from a different mode of action than that observed with cocaine. Further experiments are warranted to determine whether such undesirable effects can be potentiated under pathological conditions such as neuropathic pain, mood disorders, or addiction and to identify the key neurotransmitter system involved.

Establishing performance characteristics for positive control article selection in drug self-administration studies

The selection of a controlled substance (CS) for use as the positive control article in a nonclinical drug abuse liability (DAL) assessment study should be contemplated carefully and with full understanding of the stated intent of the study design. Any CS that can maintain day-to-day stable baseline responding of voluntary intravenous intakes in animals may be selected under the current guidelines. Schedule I - IV CNS stimulants, depressants, and sedative/hypnotics can serve as maintenance drugs in these protocols, but not all of these compounds will provide comparatively efficient, robust, and stable daily intakes. Each Sponsor is directed to select a positive control article and training dose that will provide the most balanced, predictive, and scientifically-sound comparison consistent with the mechanism of action or therapeutic target of the test article. The SA study design is not a "one-size-fits-all" assay. This is a discussion of the critical design factors to be considered in selecting the most appropriate positive control article to use for a SA study.

Drug Discrimination: Historical Origins, Important Concepts, and Principles

Research on the stimulus properties of drugs began with studies on state dependent learning during the first half of the twentieth century. From that research, an entirely new approach evolved called drug discrimination. Animals (including humans) could discriminate the presence or absence of a drug; once learned, the drug could serve as a discriminative stimulus, signaling the availability or nonavailability of reinforcement. Early drug discrimination research involved the use of a T-maze task, which evolved in the 1970s into a two-lever operant drug discrimination task that is still used today. A number of important concepts and principles of drug discrimination are discussed. (1) The discriminative stimulus properties of drugs are believed in large part to reflect the subjective effects of drugs. While it has been impossible to directly measure subjective effects in nonhuman animals, drug discrimination studies in human subjects have generally supported the belief that discriminative stimulus properties of drugs in nonhuman animals correlate highly with subjective effects of drugs in humans. In addition to the ability of the drug discrimination procedure to measure the subjective effects of drugs, it has a number of other strengths that help make it a valuable preclinical assay. (2) Drug discrimination can be used for classification of drugs based on shared discriminative stimulus properties. (3) The phenomena of tolerance and cross-tolerance can be studied with drug discrimination. (4) Discriminative stimulus properties of drugs typically have been found to be stereospecific, if a drug is comprised of enantiomers. (5) Discriminative stimulus properties of drugs reflect specific CNS activity at neurotransmitter receptors. (6) Both human and nonhuman subjects display individual differences in their sensitivity to discriminative stimuli and drugs. (7) The drug discrimination procedure has been used extensively as a preclinical assay in drug development. This chapter is the first in the volume The Behavioural Neuroscience of Drug Discrimination, which includes chapters concerning the discriminative stimulus properties of various classes of psychoactive drugs as well as sections on the applications and approaches for using this procedure.

Assessment of the Abuse Potential of Cebranopadol in Nondependent Recreational Opioid Users: A Phase 1 Randomized Controlled Study

BACKGROUND

Cebranopadol is a nociceptin/orphanin FQ peptide/opioid receptor agonist with central antinociceptive activity. We hypothesize that this novel mechanism of action may lead to a lower risk of abuse compared with pure μ-opioid peptide receptor agonists.

METHODS

We conducted a single-dose, nested-randomized, double-blind crossover study in nondependent recreational opioid users to evaluate the abuse potential of single doses of cebranopadol relative to hydromorphone immediate release and placebo. The study consisted of a qualification phase and a 7-period treatment phase (cebranopadol 200, 400, and 800 μg; hydromorphone 8 and 16 mg; and 2 placebos). The primary end point was the peak effect of drug liking at this moment, measured by visual analog scale (VAS). Various secondary end points (eg, VAS rating for good drug effects, high, bad drug effects, take drug again, drug similarity, and pupillometry) were also investigated.

RESULTS

Forty-two subjects completed the study. Cebranopadol 200 and 400 μg did not differentiate from placebo on the abuse potential assessments and generated smaller responses than hydromorphone. Responses observed with cebranopadol 800 μg were similar to hydromorphone 8 mg and smaller than hydromorphone 16 mg. The maximum effect for VAS drug liking at this moment was delayed compared with hydromorphone (3 and 1.5 hours, respectively). Cebranopadol administration was safe; no serious adverse events or study discontinuation due to treatment-emergent adverse events occurred.

CONCLUSIONS

These results confirm our hypothesis that cebranopadol, a nociceptin/orphanin FQ peptide/opioid receptor agonist, has lower abuse potential than hydromorphone immediate release, a pure μ-opioid peptide agonist.

Fentanyl: Receptor pharmacology, abuse potential, and implications for treatment

Opioid overdoses, many of which are attributed to use of illicit fentanyl, are currently one of the leading causes of death in the U.S. Although fentanyl has been used safely for decades in clinical settings, the widespread use of illicit fentanyl is a recent phenomenon. Starting in 2013, illicitly manufactured fentanyl and its analogs began to appear on the streets. These substances were added to or sold as heroin, often unbeknownst to the user. Because fentanyl is so potent, only small amounts are needed to produce pharmacological effects, but the margin between safe and toxic doses is narrow. Surprisingly little is known about the exact signaling mechanisms underlying fentanyl-related respiratory depression or the effectiveness of naloxone in reversing this effect. Similarly, little is known about the ability of treatment medications such as buprenorphine, methadone, or naltrexone to reduce illicit fentanyl use. The present article reviews the receptor, preclinical and clinical pharmacology of fentanyl, and how its pharmacology may predict the effectiveness of currently approved medications for treating illicit fentanyl use.

Reduced Nicotine Content Cigarettes and Cannabis Use in Vulnerable Populations

Objective: We estimated whether recent cannabis use moderates response to cigarettes varying in nicotine content (0.4, 2.4, 5.2, 15.8 mg/g) among smokers with concurrent affective disorders, opioid dependence, or socioeconomic disadvantage. Methods: We conducted a secondary analysis of a multi-site, double-blind, laboratory study examining acute response to reduced nicotine content cigarettes (RNCC) in 169 adult smokers with co-morbid conditions. Participants positive for recent cannabis use or self-reported past 30-day cannabis use at baseline were categorized as current cannabis users (N = 63). Repeated measures analysis of variance tests assessed whether baseline cannabis use moderated cigarette reinforcement, tobacco withdrawal, craving, smoking topography, or carbon monoxide boost. Results: Cannabis users were younger, less educated, and had more depression and anxiety than non-users (p < .05). Cannabis use status did not moderate the effects of nicotine dose on concurrent choice testing, subjective effects of RNCCs, or smoking topography. After adjusting for sociodemographic characteristics, cannabis users had higher ratings on Smoking Satisfaction, Enjoyment of Respiratory Tract Sensations, and Craving Reduction across all nicotine doses. Cannabis users reported longer withdrawal symptom duration and more rapid decline of carbon monoxide boost than non-users. Conclusions: Findings suggest RNCCs decrease the addiction potential of cigarettes in vulnerable populations independent of cannabis use status.

Prenatal ethanol exposure increases risk of psychostimulant addiction

Prenatal ethanol exposure (PE) causes many cognitive and behavioral deficits including increased drug addiction risk, demonstrated by enhanced ethanol intake and behavioral phenotypes associated with addiction risk. Additionally, preclinical studies show that PE persistently changes the function of dopaminergic neurons in the ventral tegmental area, a major neural substrate for addiction, and alters these neurons' responses to psychostimulants. Accordingly, PE could also lead to increased risk of addiction to drugs of abuse, other than ethanol. In the present study, addiction risk was examined utilizing paradigms of amphetamine conditioned place preference (CPP) and intravenous self-administration. Ethanol was administered to pregnant dams via intragastric gavage (6  g/kg, during gestational days 8-20). Behavioral tests were conducted in adult male offspring. Amphetamine at a low dose (0.3  mg/kg, i.p.) induced CPP in PE but not control rats, whereas at a higher dose (0.6  mg/kg, i.p.) both groups acquired CPP. There was no group difference in amphetamine-induced CPP reinstatement. Furthermore, PE rats self-administered more amphetamine at a low dose (0.02  mg/kg/infusion) than controls, while no group differences were observed at a higher dose (0.1  mg/kg/infusion). Rats with PE also exhibited greater reactivity to contextual drug cues after extended abstinence and amphetamine-induced reinstatement of drug seeking. These results support that PE persistently leads to increased psychostimulant addiction risk later in life, manifested in many elements of addictive behavior following limited psychostimulant exposure. The observations provide insights into prevention strategies for drug addiction in individuals with fetal alcohol spectrum disorders.

21st century neurobehavioral theories of decision making in addiction: Review and evaluation

This review critically examines neurobehavioral theoretical developments in decision making in addiction in the 21st century. We specifically compare each theory reviewed to seven benchmarks of theoretical robustness, based on their ability to address: why some commodities are addictive; developmental trends in addiction; addiction-related anhedonia; self-defeating patterns of behavior in addiction; why addiction co-occurs with other unhealthy behaviors; and, finally, means for the repair of addiction. We have included only self-contained theories or hypotheses which have been developed or extended in the 21st century to address decision making in addiction. We thus review seven distinct theories of decision making in addiction: learning theories, incentive-sensitization theory, dopamine imbalance and systems models, opponent process theory, strength models of self-control failure, the competing neurobehavioral decision systems theory, and the triadic systems theory of addiction. Finally, we have directly compared the performance of each of these theories based on the aforementioned benchmarks, and highlighted key points at which several theories have coalesced.

A regulatory perspective on the evaluation of hallucinogen drugs for human use

In recent years, there is renewed interest in the study of various hallucinogens for their potential therapeutic effects. In the United States of America (USA), the abuse potential assessment of a drug is carried out as part of the general safety and efficacy evaluation of a drug. Additionally, the abuse potential assessment is taken under consideration in determining if a drug needs to be subject to controls to minimize the abuse of the drug once on the market. This assessment is conducted for all new drugs with central nervous system (CNS) activity, that are chemically or pharmacologically similar to other drugs with known abuse potential, or drugs that produce psychoactive effects predictive of abuse, such as euphoria and hallucinations. This paper describes the regulatory framework for evaluating the abuse potential of new drugs, with emphasis on hallucinogens. The paper discusses the role of the United States Food and Drug Administration (FDA) in the evaluation of the abuse potential of drugs and its role in drug control, and provides an overview of the controlled status of hallucinogens and the requirements to conduct research with Schedule I substances in the USA. This article is part of the Special Issue entitled 'Psychedelics: New Doors, Altered Perceptions'.

Addiction Potential of Cigarettes With Reduced Nicotine Content in Populations With Psychiatric Disorders and Other Vulnerabilities to Tobacco Addiction

IMPORTANCE

A national policy is under consideration to reduce the nicotine content of cigarettes to lower nicotine addiction potential in the United States.

OBJECTIVE

To examine how smokers with psychiatric disorders and other vulnerabilities to tobacco addiction respond to cigarettes with reduced nicotine content.

DESIGN, SETTING, AND PARTICIPANTS

A multisite, double-blind, within-participant assessment of acute response to research cigarettes with nicotine content ranging from levels below a hypothesized addiction threshold to those representative of commercial cigarettes (0.4, 2.3, 5.2, and 15.8 mg/g of tobacco) at 3 academic sites included 169 daily smokers from the following 3 vulnerable populations: individuals with affective disorders (n = 56) or opioid dependence (n = 60) and socioeconomically disadvantaged women (n = 53). Data were collected from March 23, 2015, through April 25, 2016.

INTERVENTIONS

After a brief smoking abstinence, participants were exposed to the cigarettes with varying nicotine doses across fourteen 2- to 4-hour outpatient sessions.

MAIN OUTCOMES AND MEASURES

Addiction potential of the cigarettes was assessed using concurrent choice testing, the Cigarette Purchase Task (CPT), and validated measures of subjective effects, such as the Minnesota Nicotine Withdrawal Scale.

RESULTS

Among the 169 daily smokers included in the analysis (120 women [71.0%] and 49 men [29.0%]; mean [SD] age, 35.6 [11.4] years), reducing the nicotine content of cigarettes decreased the relative reinforcing effects of smoking in all 3 populations. Across populations, the 0.4-mg/g dose was chosen significantly less than the 15.8-mg/g dose in concurrent choice testing (mean [SEM] 30% [0.04%] vs 70% [0.04%]; Cohen d = 0.40; P < .001) and generated lower demand in the CPT (α = .027 [95% CI, 0.023-0.031] vs α = .019 [95% CI, 0.016-0.022]; Cohen d = 1.17; P < .001). Preference for higher over lower nicotine content cigarettes could be reversed by increasing the response cost necessary to obtain the higher dose (mean [SEM], 61% [0.02%] vs 39% [0.02%]; Cohen d = 0.40; P < .001). All doses reduced Minnesota Nicotine Withdrawal Scale total scores (range of mean decreases, 0.10-0.50; Cohen d range, 0.21-1.05; P < .001 for all), although duration of withdrawal symptoms was greater at higher doses (η2 = 0.008; dose-by-time interaction, P = .002).

CONCLUSIONS AND RELEVANCE

Reducing the nicotine content of cigarettes may decrease their addiction potential in populations that are highly vulnerable to tobacco addiction. Smokers with psychiatric conditions and socioeconomic disadvantage are more addicted and less likely to quit and experience greater adverse health impacts. Policies to reduce these disparities are needed; reducing the nicotine content in cigarettes should be a policy focus.

The Abuse Potential of Prescription Opioids in Humans-Closing in on the First Century of Research

While opioids are very effective analgesics for treating acute pain, humans have struggled with opiate addiction for millenia. An opium abuse epidemic in the early 1900's led the US government to develop a systematic research infrastructure and scientific plan to produce new compounds with analgesic properties but without abuse liability. This review describes the techniques that were developed for testing in the human laboratory, including empirically derived outcome measures and required elements for human abuse potential assessment. The evaluation and characterization of semi-synthetic and synthetic opioids, including full mu opioid agonists, partial agonists and mixed agonist-antagonists, are described across several decades of research. Finally, the prescription opioid epidemic beginning in the 1990's in the US led to a resurgence in abuse potential evaluations, and the application of these methods to the study of novel abuse-deterrent formulations is discussed.

Assessment of the Abuse Potential of the Orexin Receptor Antagonist, Suvorexant, Compared With Zolpidem in a Randomized Crossover Study

Suvorexant is a dual orexin receptor antagonist approved in the United States and Japan for the treatment of insomnia at a maximum dose of 20 mg. This randomized double-blind crossover study evaluated the abuse potential of suvorexant in 36 healthy recreational polydrug users with a history of sedative and psychedelic drug use. Single doses of suvorexant (40, 80, and 150 mg: 2-7.5 × maximum dose), zolpidem (15 and 30 mg: 1.5-3 × maximum dose), and placebo were administered, with a 10-day washout between treatments. Subjective and objective measures, including visual analog scales (VASs), Addiction Research Center Inventory, and cognitive/psychomotor tests, were evaluated for 24-hour postdose. Suvorexant had significantly greater peak effects on "drug liking" VAS (primary endpoint) than placebo. Although effects of suvorexant on abuse potential measures were generally similar to zolpidem, they remained constant across doses, whereas zolpidem often had greater effects at higher doses. Suvorexant (all doses) had significantly fewer effects than zolpidem 30 mg on secondary measures, such as "high" VAS, Bowdle VAS, and Addiction Research Center Inventory morphine-benzedrine group. The overall incidence of abuse-related adverse events, such as euphoric mood and hallucination, was numerically lower with suvorexant than zolpidem. In agreement with its classification as a schedule IV drug, suvorexant demonstrated abuse potential, compared with placebo. The abuse potential was similar to zolpidem using certain measures, but with a reduced incidence of abuse-related adverse events. Although this suggests that the overall abuse liability of suvorexant may be lower than zolpidem, the actual abuse rates will be assessed with the postmarketing experience.

Abuse liability assessment of eslicarbazepine acetate in healthy male and female recreational sedative users: A Phase I randomized controlled trial

RATIONALE

Eslicarbazepine acetate (ESL) is a once-daily oral antiepileptic drug for the treatment of partial-onset seizures. Adverse events such as dizziness and somnolence reported in clinical studies suggest that ESL has detectable central nervous system (CNS) effects in addition to its antiepileptic effects. This Phase I study evaluated the abuse liability of ESL compared with that of alprazolam (ALP) and placebo (PBO) in recreational CNS depressant users.

METHODS

In this single-dose, randomized, double-blind, PBO- and active-controlled crossover study, healthy recreational CNS depressant users who could discern between ALP 2mg and PBO received single oral doses of each of the following treatments with a washout interval of ≥7days between each treatment: ESL (800mg, 1600mg, 2000mg, and 2400mg); ALP (1.5mg and 3.0mg); and PBO. Subjective measures, including visual analog scales (VASs) e.g., Drug-Liking (primary endpoint), and Addiction Research Center Inventory (ARCI) Morphine-Benzedrine Group (MBG), Pentobarbital Chlorpromazine Alcohol Group (PCAG), and Lysergic Acid Diethylamide Group scales were evaluated at multiple time points up to 24h postdose. Cognitive effects were evaluated using the Choice Reaction Time (CRT), Divided Attention (DAT) and Hopkins Verbal Learning Task-Revised tests.

PRINCIPAL RESULTS

Peak scores for Drug-Liking VAS (maximum effect [Emax]) were significantly higher for both ALP doses than for PBO (p<0.0001), thereby confirming study validity. Drug-Liking VAS Emax was significantly lower for all ESL doses than both ALP doses (p<0.0001). Drug-Liking VAS Emax for ESL 800mg was similar to that for PBO (least squares [LS] mean difference: 3.6; p=0.19). At the three higher ESL doses (1600mg and the supratherapeutic doses of 2000mg and 2400mg), Drug-Liking VAS Emax was significantly higher than for PBO, although the differences were minimal (LS mean difference: 9.3-13.3 out of 100). For most secondary subjective endpoints (i.e., Good Effects VAS and High VAS, ARCI-MBG, Take Drug Again VAS, Overall Drug-Liking VAS, and ARCI-PCAG; p<0.05), the effect of ESL (all doses) was significantly less than that of ALP (both doses). On most secondary measures, the dose-response relationship was relatively flat or showed saturation at higher ESL doses. Although significant differences were observed for ESL compared with those for PBO for some specific CRT and DAT endpoints (i.e., reaction time, manual tracking, hit latency), ALP demonstrated significant and dose-dependent impairment on the majority of cognitive endpoints when compared with PBO and ESL. Mean plasma concentrations of the active metabolite of ESL, eslicarbazepine, increased with increasing ESL dose. Pharmacokinetic parameters estimated for eslicarbazepine were generally comparable with results from previous studies in healthy volunteers.

CONCLUSION

This study demonstrated that single doses of ESL may have less abuse liability than ALP in recreational sedative users. Although ESL had detectable subjective effects and showed some drug-'liking' at higher doses, the magnitude of these effects was small.

Need for Analgesics/drugs of Abuse: A Comparison Between Headache Patients and Addicts by the Leeds Dependence Questionnaire (LDQ)

Our aim was to compare the need for analgesics/drugs of abuse between headache patients—chronic and episodic headache sufferers—and addicts, by the Leeds Dependence Questionnaire (LDQ). This is a self-completion 10-item instrument to measure dependence upon a variety of substances. We administered the LDQ questionnaire to 122 chronic daily headache (CDH) sufferers who had been taking one dose of analgesic drug every day for at least 1 year; 71 subjects suffering from episodic headache (EH) using analgesics only occasionally; 115 consecutive drug addicts (DA) with a diagnosis of substance dependence. The mean LDQ total score was similar in the CDH (11.58 ± 6.35) and DA (10.37 ± 6.51) groups, and for both it was significantly higher than the score in the EH (5.61 ± 3.00) group ( P < 0.001). The CDH group had the highest scores, and higher scores than the DA group (Z = −8.18, P < 0.001) in item 8, assessing the primacy of effect over the kind of analgesic used, and in item 10 (Z = −5.03, P < 0.001), asking if it is difficult to live without the analgesic; the DA group had the highest scores, and higher scores than the CDH group, in item 9 (Z = −5.07, P < 0.001) addressing the need for the continued administration of the drug to maintain well-being, and in item 3 (Z =−2.39, P < 0.05), exploring compulsion to start the use of the drug. The EH group had lower scores in all items ( P < 0.05) except for item 9, where there was no difference from CDH group; the EH group had also lower scores ( P < 0.001) than the DA group, except for item 8, where, instead, the score was higher than in the DA group (Z = −5.33, P < 0.001). A strong link develops between chronic headache patients and the analgesics they use. This sort of ‘dependence’ appears to be a consequence of headache, originating from the necessity for the analgesic to cope with everyday life.

The ketamine-like compound methoxetamine substitutes for ketamine in the self-administration paradigm and enhances mesolimbic dopaminergic transmission

RATIONALE

Recently, an increasing number of emergency cases due to a novel ketamine-like drug, methoxetamine (MXE), were reported in several countries. However, very little is known about the neuropsychopharmacological and reinforcing profile of this compound.

OBJECTIVES

Our study aims to investigate the effects of MXE on self-administration (SA) behaviour in comparison to ketamine and on dopaminergic transmission.

METHODS

A SA substitution study was performed in male rats trained to intravenously (IV) self-administer ketamine. At responding stability, rats were exposed to sequential phases of MXE substitution at different dosages (starting from 0.5 and then decreasing to 0.25 and 0.125 mg/kg). Standard electrophysiological techniques were used to record changes in firing activities of ventral tegmental area (VTA) dopamine neurons projecting to the nucleus accumbens (NAc) shell after acute injection of cumulative doses of MXE (0.031-0.5 mg/kg IV). Finally, in vivo microdialysis was performed in freely moving rats to evaluate the effect of acute MXE administration (0.125, 0.25 and 0.5 mg/kg IV) on dopamine release in the NAc shell.

RESULTS

MXE 0.125 and 0.25 mg/kg, but not 0.5 mg/kg, substituted for ketamine SA. MXE also induced a dose-dependent stimulation of firing rate (p < 0.0001) and burst firing (p < 0.05) of NAc-projecting VTA dopamine neurons. Consistently, MXE significantly (p < 0.05) increased dopamine extracellular levels in the NAc shell at 0.5 and 0.25 mg/kg with different time onsets, i.e. at 40 and 100 min, respectively.

CONCLUSIONS

This study, while confirming the reinforcing effects of MXE, highlights an electrophysiological and neurochemical profile predictive of its addictive properties.

Assessment of human abuse potential of dasotraline compared to methylphenidate and placebo in recreational stimulant users

AIMS

The aim of this study was to evaluate the abuse potential of dasotraline, a novel dopamine and norepinephrine reuptake inhibitor with slow absorption (tmax, 10-12h) and elimination (t1/2=47-77 h) that is in development for the treatment of attention deficit hyperactivity disorder (ADHD).

METHODS

Recreational stimulant users (N=48) who had specific experience with cocaine, and who were able to distinguish methylphenidate (60 mg) versus placebo in a qualification session, were randomized, in a 6-period, double-blind, crossover design, to receive single doses of dasotraline 8 mg, 16 mg, and 36 mg, methylphenidate (MPH) 40 mg and 80 mg, and placebo. The primary endpoint was the Drug Liking Visual Analog Scale (VAS) score at the time of peak effect (Emax).

RESULTS

There were no significant differences between the 3 doses of dasotraline and placebo on the drug liking VAS at Emax, and on most secondary endpoints. Both doses of MPH had significantly higher VAS-drug liking scores at Emax relative to both placebo (P<0.001 for all comparisons) and dasotraline 8 mg (P<0.001), 16 mg (P<0.001) and 36 mg (P<0.01). The increase in heart rate for MPH and dasotraline 36 mg showed a time-course that closely matched subject-rated measures such as Any Effects VAS.

CONCLUSIONS

In this study, dasotraline was found to have low potential for abuse, which may be, in part, related to its established pharmacokinetics (PK) profile, which is characterized by slow absorption and gradual elimination.

Abuse Potential of Pregabalin: A Systematic Review

BACKGROUND

Several case reports and epidemiological studies have raised concern about the abuse potential of pregabalin, the use of which has increased substantially over the last decade. Pregabalin is, in some cases, used for recreational purposes and it has incurred attention among drug abusers for causing euphoric and dissociative effects when taken in doses exceeding normal therapeutic dosages or used by alternative routes of administration, such as nasal insufflation or venous injection. The magnitude of the abuse potential and the mechanism behind it are not fully known.

OBJECTIVE

The aim of this study was to present a systematic review of the data concerning the abuse potential of pregabalin.

METHODS

We performed a systematic literature search and reviewed the preclinical, clinical and epidemiological data on the abuse potential of pregabalin.

RESULTS

We included preclinical (n = 17), clinical (n = 19) and epidemiological (n = 13) studies addressing the abuse potential of pregabalin. We also reviewed case reports (n = 9) concerning abuse of pregabalin. The preclinical studies indicated that pregabalin possesses modulatory effects on the GABA and glutamate systems, leaving room for an abuse potential. Further, clinical studies reported euphoria as a frequent side effect in patients treated with pregabalin. The majority of case reports concerning abuse of pregabalin involved patients with a history of substance abuse and, similarly, epidemiological studies found evidence of abuse, especially among opiate abusers.

CONCLUSIONS

Overall, the available literature suggests an important clinical abuse potential of pregabalin and prescribers should pay attention to signs of abuse, especially in patients with a history of substance abuse.

Assessment of Pharmacokinetic and Pharmacodynamic Interactions Between Albumin-Fused Mutated Butyrylcholinesterase and Intravenously Administered Cocaine in Recreational Cocaine Users

Cocaine dependence presents a major public health issue, and to date, no pharmacotherapies are approved for its treatment. TV-1380 is a novel recombinant albumin-fused mutated butyrylcholinesterase (Albu-BChE) that has increased catalytic efficiency for cocaine compared with wild-type BChE and therefore has the potential to facilitate abstinence in cocaine-dependent subjects by decreasing exposure to cocaine and its reinforcing effects.

METHODS

This randomized, double-blind, placebo-controlled, parallel-group study in nondependent cocaine users was conducted to evaluate the effect of a single intramuscular dose of Albu-BChE (50, 100, and 300 mg) on the pharmacokinetic and metabolic profile of intravenous cocaine infusions (40 mg) administered at baseline and at 24, 96, and 168 hours after Albu-BChE dosing, to assess safety of coadministering Albu-BChE and cocaine, and to explore the subjective responses to cocaine infusions after Albu-BChE dosing.

RESULTS

Administration of Albu-BChE resulted in significant dose-dependent reductions in cocaine exposure (maximum concentration, area under the curve) and half-life. Effects were greatest at 24 hours after Albu-BChE dose, but were sustained up to 168 hours. Spearman correlations indicated a significant negative relationship between Albu-BChE concentration and cocaine clearance and exposure. Consistent with its mechanism of action, Albu-BChE also shifted cocaine metabolism toward preferential formation of ecgonine methyl ester. Administration of Albu-BChE was associated with modest decreases in subjective reports of feeling high and willingness to take cocaine again after cocaine infusion. Coadministration of Albu-BChE and cocaine was safe and well tolerated.

CONCLUSIONS

Administration of Albu-BChE at single doses of 50, 100, and 300 mg safely resulted in long-lasting decreases in cocaine exposure in recreational cocaine users.

Comparing the Effect of Tampering on the Oral Pharmacokinetic Profiles of Two Extended-Release Oxycodone Formulations with Abuse-Deterrent Properties

OBJECTIVE

Oxycodone DETERx® is an extended-release (ER), microsphere-in-capsule abuse-deterrent-formulation designed to retain its extended-release properties following tampering or misuse (e.g., chewing, crushing). This study assessed the safety and pharmacokinetics of orally administered intact and crushed Oxycodone DETERx® capsules compared with intact and crushed reformulated OxyContin® tablets and crushed immediate-release oxycodone tablets (IR oxycodone).

METHODS

This was a randomized, open-label, active-controlled, cross-over study. Healthy subjects received five oxycodone treatments (40 mg) with a standardized high-fat, high-calorie meal: Oxycodone DETERx® (intact or crushed), OxyContin® (intact or crushed), and IR oxycodone (crushed). Blood samples were collected for assessment of oxycodone plasma concentrations.

RESULTS

Thirty-eight subjects completed the study. Both crushed and intact Oxycodone DETERx® resulted in lower peak plasma concentrations when compared with IR oxycodone. Crushed Oxycodone DETERx® was bioequivalent to intact Oxycodone DETERx® and exhibited a numerically lower Cmax . Also, median Tmax was unchanged by crushing. In contrast, mean peak plasma oxycodone concentrations for crushed OxyContin® were significantly higher compared with intact OxyContin® and were bioequivalent to IR oxycodone. Median Tmax for crushed OxyContin® was the same as IR oxycodone and 3.25 hours shorter than intact OxyContin®.

CONCLUSIONS

These data demonstrate that when crushed and taken orally, Oxycodone DETERx® maintains its EXTENDED-release profile, while crushed OxyContin® shows a pharmacokinetic profile similar to an immediate-release product. These results suggest that Oxycodone DETERx® may be less attractive to illicit drug users compared with existing abuse-deterrent-formulations, while providing a safer option for patients who may unknowingly crush their medication such as those who have difficulty swallowing.

Regulatory acceptance of animal models of disease to support clinical trials of medicines and advanced therapy medicinal products

The utility of animal models of disease for assessing the safety of novel therapeutic modalities has become an increasingly important topic of discussion as research and development efforts focus on improving the predictive value of animal studies to support accelerated clinical development. Medicines are approved for marketing based upon a determination that their benefits outweigh foreseeable risks in specific indications, specific populations, and at specific dosages and regimens. No medicine is 100% safe. A medicine is less safe if the actual risks are greater than the predicted risks. The purpose of preclinical safety assessment is to understand the potential risks to aid clinical decision-making. Ideally preclinical studies should identify potential adverse effects and design clinical studies that will minimize their occurrence. Most regulatory documents delineate the utilization of conventional "normal" animal species to evaluate the safety risk of new medicines (i.e., new chemical entities and new biological entities). Animal models of human disease are commonly utilized to gain insight into the pathogenesis of disease and to evaluate efficacy but less frequently utilized in preclinical safety assessment. An understanding of the limitations of the animal disease models together with a better understanding of the disease and how toxicity may be impacted by the disease condition should allow for a better prediction of risk in the intended patient population. Importantly, regulatory authorities are becoming more willing to accept and even recommend data from experimental animal disease models that combine efficacy and safety to support clinical development.

Electronic cigarettes: abuse liability, topography and subjective effects

Objective

To review the available evidence evaluating the abuse liability, topography, subjective effects, craving and withdrawal suppression associated with e-cigarette use in order to identify information gaps and provide recommendations for future research.

Methods

Literature searches were conducted between October 2012 and January 2014 using five electronic databases. Studies were included in this review if they were peer-reviewed scientific journal articles evaluating clinical laboratory studies, national surveys or content analyses.

Results

A total of 15 peer-reviewed articles regarding behavioural use and effects of e-cigarettes published between 2010 and 2014 were included in this review. Abuse liability studies are limited in their generalisability. Topography (consumption behaviour) studies found that, compared with traditional cigarettes, e-cigarette average puff duration was significantly longer, and e-cigarette use required stronger suction. Data on e-cigarette subjective effects (such as anxiety, restlessness, concentration, alertness and satisfaction) and withdrawal suppression are limited and inconsistent. In general, study data should be interpreted with caution, given limitations associated with comparisons of novel and usual products, as well as the possible effects associated with subjects’ previous experience/inexperience with e-cigarettes.

Conclusions

Currently, very limited information is available on abuse liability, topography and subjective effects of e-cigarettes. Opportunities to examine extended e-cigarette use in a variety of settings with experienced e-cigarette users would help to more fully assess topography as well as behavioural and subjective outcomes. In addition, assessment of ‘real-world’ use, including amount and timing of use and responses to use, would clarify behavioural profiles and potential adverse health effects.

Preclinical Abuse Potential Assessment

Although laboratories have been conducting scientific evaluations of the abused drugs for many years, preclinical evaluations of the abuse potential of new drugs have been an integral component of new drug applications more recently. The development of a unified testing approach is crucial prior to initiating individual studies to address abuse potential. The core preclinical studies that will be required include a dependence/withdrawal study, an assessment of the discriminative cue produced by the new drug, and an assessment of whether the drug will be self-administered. This discussion is focused on the requirements for drug scheduling recommendations from the FDA and how to conduct the evaluations that will be used to make those recommendations and how to select parameter details such as preclinical species, test doses, test conditions, route of drug administration, comparator compounds, and behavioral test designs recommended.

Intracranial self-stimulation to evaluate abuse potential of drugs

Intracranial self-stimulation (ICSS) is a behavioral procedure in which operant responding is maintained by pulses of electrical brain stimulation. In research to study abuse-related drug effects, ICSS relies on electrode placements that target the medial forebrain bundle at the level of the lateral hypothalamus, and experimental sessions manipulate frequency or amplitude of stimulation to engender a wide range of baseline response rates or response probabilities. Under these conditions, drug-induced increases in low rates/probabilities of responding maintained by low frequencies/amplitudes of stimulation are interpreted as an abuse-related effect. Conversely, drug-induced decreases in high rates/probabilities of responding maintained by high frequencies/amplitudes of stimulation can be interpreted as an abuse-limiting effect. Overall abuse potential can be inferred from the relative expression of abuse-related and abuse-limiting effects. The sensitivity and selectivity of ICSS to detect abuse potential of many classes of abused drugs is similar to the sensitivity and selectivity of drug self-administration procedures. Moreover, similar to progressive-ratio drug self-administration procedures, ICSS data can be used to rank the relative abuse potential of different drugs. Strengths of ICSS in comparison with drug self-administration include 1) potential for simultaneous evaluation of both abuse-related and abuse-limiting effects, 2) flexibility for use with various routes of drug administration or drug vehicles, 3) utility for studies in drug-naive subjects as well as in subjects with controlled levels of prior drug exposure, and 4) utility for studies of drug time course. Taken together, these considerations suggest that ICSS can make significant contributions to the practice of abuse potential testing.

Human abuse liability evaluation of CNS stimulant drugs

Psychoactive drugs that increase alertness, attention and concentration and energy, while also elevating mood, heart rate and blood pressure are referred to as stimulants. Despite some overlapping similarities, stimulants cannot be easily categorized by their chemical structure, mechanism of action, receptor binding profile, effects on monoamine uptake, behavioral pharmacology (e.g., effects on locomotion, temperature, and blood pressure), therapeutic indication or efficacy. Because of their abuse liability, a pre-market assessment of abuse potential is required for drugs that show stimulant properties; this review article focuses on the clinical aspects of this evaluation. This includes clinical trial adverse events, evidence of diversion or tampering, overdoses and the results of a human abuse potential study. While there are different types of human experimental studies that can be employed to evaluate stimulant abuse potential (e.g., drug discrimination, self-administration), only the human abuse potential study and clinical trial adverse event data are required for drug approval. The principal advances that have improved human abuse potential studies include using study enrichment strategies (pharmacologic qualification), larger sample sizes, better selection of endpoints and measurement strategies and more carefully considered interpretation of data. Because of the methodological advances, comparisons of newer studies with historical data is problematic and may contribute to a biased regulatory framework for the evaluation of newer stimulant-like drugs, such as A2 antagonists. This article is part of the Special Issue entitled 'CNS Stimulants'.

A regulatory perspective on the abuse potential evaluation of novel stimulant drugs in the United States

In the United States of America (USA), the abuse potential assessment of a drug is performed as part of the safety evaluation of a drug under development, and to evaluate if the drug needs to be subject to controls that would minimize the abuse of the drug once on the market. The assessment of the abuse potential of new drugs consists of a scientific and medical evaluation of all data related to abuse of the drug. This paper describes the regulatory framework for evaluating the abuse potential of new drugs, in general, including novel stimulants. The role of the United States Food and Drug Administration (FDA) in the evaluation of the abuse potential of drugs, and its role in drug control are also discussed. A definition of abuse potential, an overview of the currently accepted approaches to evaluating the abuse potential of a drug, as well as a description of the criteria that applies when recommending a specific level of control (i.e., a Schedule) for a drug under the Controlled Substances Act (CSA). This article is part of the Special Issue entitled 'CNS Stimulants'.

Predicting abuse potential of stimulants and other dopaminergic drugs: overview and recommendations

Examination of a drug's abuse potential at multiple levels of analysis (molecular/cellular action, whole-organism behavior, epidemiological data) is an essential component to regulating controlled substances under the Controlled Substances Act (CSA). We reviewed studies that examined several central nervous system (CNS) stimulants, focusing on those with primarily dopaminergic actions, in drug self-administration, drug discrimination, and physical dependence. For drug self-administration and drug discrimination, we distinguished between experiments conducted with rats and nonhuman primates (NHP) to highlight the common and unique attributes of each model in the assessment of abuse potential. Our review of drug self-administration studies suggests that this procedure is important in predicting abuse potential of dopaminergic compounds, but there were many false positives. We recommended that tests to determine how reinforcing a drug is relative to a known drug of abuse may be more predictive of abuse potential than tests that yield a binary, yes-or-no classification. Several false positives also occurred with drug discrimination. With this procedure, we recommended that future research follow a standard decision-tree approach that may require examining the drug being tested for abuse potential as the training stimulus. This approach would also allow several known drugs of abuse to be tested for substitution, and this may reduce false positives. Finally, we reviewed evidence of physical dependence with stimulants and discussed the feasibility of modeling these phenomena in nonhuman animals in a rational and practical fashion. This article is part of the Special Issue entitled 'CNS Stimulants'.

The CYP2D6 gene determines oxycodone's phenotype-specific addictive potential: implications for addiction prevention and treatment

We propose a hypothesis for predicting addictive potential of oral drugs, in general, and oxycodone's addictive potential, in particular. We hypothesize that a patient's CYP2D6 phenotype determines oxycodone's addictive potential, in part, via genotype-specific regulation of its clearance; although, other possible modulators of oxycodone's addiction potential exist. For example, brain CYPs related to phenotype could be involved. To pilot test our hypothesis, we used a mathematical model which postulates that oxycodone's addictive potential is given by: LAP=E/(ka/ke), where LAP represents addictive potential, E represents euphoric potency, ka is the absorption rate constant of drug from the gastrointestinal tract, and ke is the systemic elimination rate constant of drug by all processes responsible for its removal from plasma. Using CYP2D6 phenotype-specific oxycodone pharmacokinetic parameter values derived from published data, our hypothesis predicted that the canonical order of oxycodone's addictive potential was UM>EM>IM>PM, with corresponding LAP values of 0.24, 0.21, 0.17, and 0.15 respectively. Our hypothesis about oxycodone's addictive potential may provide a unifying approach useful for both personalized medicine dosing and predicting addictive potential of oral drugs in humans, since it is based on both oxycodone's pharmacogenetics and pharmacokinetics.

Principles of assessment of abuse liability: US legal framework and regulatory environment

Identifying the abuse potential of drug products in the premarketing and postmarketing environment has been a critical component in the implementation of drug abuse control laws worldwide. In the US, the Controlled Substances Act of 1970 (CSA) is a comprehensive federal law enacted to prevent the abuse or diversion of substances with abuse liability or addiction potential (for present purposes, these terms are used interchangeably). Under the jurisdiction of the Drug Enforcement Administration, the law applies to the manufacture and distribution of narcotics and other drug substances with potential of abuse. The CSA classifies substances with abuse potential into schedules I-V based on the substance's risk of diversion or abuse, and thus provides a legal framework for the assessment of abuse liability of New Molecular Entities. When the Food and Drug Administration reviews the safety and efficacy of a New Drug Application it also determines whether the drug has potential for abuse, and if so, will begin the process to schedule the drug under the CSA. As the assessment of abuse potential is a critical component of a marketing application, pharmaceutical companies (sponsors) bear the responsibility of generating a comprehensive preclinical and clinical data package for regulators to review and make decisions on labeling and the corresponding postmarketing surveillance. Recent regulatory guidelines adopted in the European Union (EU) (2006), Canada (2007), and USA (2010) provide recommendations to sponsors on preclinical and clinical methodologies for the assessment of abuse potential. This paper reviews the legal framework of the assessment of abuse liability and scheduling of controlled substances in the USA and describes the current global regulatory environment and the challenges that sponsors and regulators face when assessing abuse liability of New Molecular Entities, from the early stages of development through the late stages, review, and approval.

Opioid abusers' ability to differentiate an opioid from placebo in laboratory challenge testing

BACKGROUND

Abuse liability assessments influence drug development, federal regulation, and clinical care. One suggested procedure to reduce variability of assessments is a qualification phase, which assesses whether study applicants adequately distinguish active drug from placebo; applicants failing to make this distinction are disqualified. The present analyses assessed differences between qualification phase qualifiers and non-qualifiers.

METHODS

Data were collected from 23 completers of the qualification phase of an abuse liability study. Opioid abusing participants received 30 mg oxycodone and placebo orally on separate days, and were characterized as qualifiers (vs. non-qualifiers) if their peak visual analog scale liking rating for oxycodone was at least 20 points higher than placebo's peak rating. Groups were compared on demographic characteristics, drug history, and physiologic, subject and observer ratings.

RESULTS

61% of participants were qualifiers and 39% were non-qualifiers. Groups had similar demographic characteristics, drug use histories, and pupillary constriction responses. However, unlike qualifiers, non-qualifiers had an exaggerated placebo response for the liking score (p=0.03) and an attenuated oxycodone response for the liking score (p<0.0001). Non-qualifiers' failure to differentiate oxycodone versus placebo was evident for subject and observer ratings.

CONCLUSION

Different subjective responses to identical stimuli support the use of a qualification phase in abuse liability assessments. Further research should explore objective measures that may better account for these differences, determine optimal qualification criteria, and explore the developmental course of drug use. This study also documents certain opioid abusers fail to differentiate 30 mg of oxycodone from placebo, a phenomenon deserving further study.

An equivalence test for the comparison between a test drug and placebo in human abuse potential studies

Statistical methodologies for human abuse potential studies are rarely evaluated. Human abuse potential studies assess whether test drugs produce positive and negative subjective responses on abuse-related measures using volunteers with histories of recreational drug use. These studies typically have a randomized, double-blind, placebo- and positive-controlled crossover design with at least four treatments: placebo, at least two doses of a test drug, and at least one dose of a positive control drug (a drug with known abuse potential). This article proposes a new test for assessing whether a test drug produces data indicative of abuse potential when compared to placebo.

Use of intracranial self-stimulation to evaluate abuse-related and abuse-limiting effects of monoamine releasers in rats

BACKGROUND AND PURPOSE

Monoamine releasers constitute a class of drugs that promote the release of dopamine (DA), serotonin (5-HT) and/or norepinephrine. Although some drugs in this class are well-known drugs of abuse (amphetamine, methamphetamine), others are thought to have reduced (3,4-methylenedioxy-N-methylamphetamine [MDMA]) or no (fenfluramine) abuse potential. The purpose of this study was to further elucidate the role of dopamine versus serotonin selectivity on expression of abuse-related effects produced by monoamine releasers in an assay of intracranial self-stimulation (ICSS) in rats.

EXPERIMENTAL APPROACH

This study evaluated effects produced in a frequency-rate ICSS procedure by 11 monoamine releasers that vary in selectivity to release DA versus 5-HT.

KEY RESULTS

Efficacy of monoamine releasers to facilitate ICSS correlated with DA-selectivity, such that DA-selective releasers exclusively facilitated ICSS, a 5-HT-selective releaser exclusively depressed ICSS, and mixed-action releasers both facilitated low ICSS rates and depressed high ICSS rates. Fixed-proportion mixtures of a DA-selective releaser and a 5-HT-selective releaser recapitulated effects of mixed-action releasers. Efficacy of monoamine releasers to facilitate ICSS also correlated with previously published data on efficacy to maintain self-administration in rhesus monkeys responding under a progressive-ratio schedule of reinforcement.

CONCLUSIONS AND IMPLICATIONS

These data support the importance of selectivity for DA versus 5-HT in determining abuse potential of monoamine releasers and demonstrate a novel correlation between rat ICSS and nonhuman primate self-administration measures of abuse-related effects. Taken together, these results support the use of ICSS in rats as an experimental tool to study the expression and pharmacological determinants of abuse-related effects of monoamine releasers.

OPPIDUM surveillance program: 20 years of information on drug abuse in France

It is important to assess drug abuse liability in 'real life' using different surveillance systems. Some are based on specific population surveys, such as individuals with drug abuse or dependence, or under opiate maintenance treatment, because this population is very familiar with drugs and is more likely to divert or abuse them. In France, an original surveillance system based on this specific population and called 'Observation of illegal drugs and misuse of psychotropic medications (OPPIDUM) survey' was set up in 1990 as the first of its kind. The aim of this article is to describe this precursor of French drug abuse surveillance using different examples, to demonstrate its ability to effectively give health authorities and physicians interesting data on drug abuse. OPPIDUM is an annual, cross-sectional survey that anonymously collects information on abuse and dependence observed in patients recruited in specialized care centers dedicated to drug dependence. From 1990 to 2010, a total of 50,734 patients were included with descriptions of 102,631 psychoactive substance consumptions. These data have outlined emergent behaviors such as the misuse of buprenorphine by intravenous or nasal administration. It has contributed to assess abuse liability of emergent drugs such as clonazepam or methylphenidate. This surveillance system was also able to detect the decrease of flunitrazepam abuse following implementation of regulatory measures. OPPIDUM's twenty years of experience clearly demonstrate that collection of valid and useful data on drug abuse is possible and can provide helpful information for physicians and health authorities.

Pharmaceutical Regulation Failures and Changes

OxyContin, a controlled-release opioid developed and produced by Purdue Pharma, was given Food and Drug Administration (FDA) approval in December 1995. By 1999, to the apparent surprise of Purdue Pharma, the Drug Enforcement Administration (DEA), and the FDA, extensive reports of OxyContin abuse and diversion began to circulate. The drug abuse assessment liability system in the United States has often been criticized and the experience with OxyContin did nothing but buttress those criticisms. However, as seven investigational hearings conducted by the U.S. Congress would expose, several changes were made to the abuse liability assessment to correct deficiencies in the system which had aggravated OxyContin abuse and diversion—a welcome sign from what many have considered an American tragedy.