Evaluating the Abuse Potential of Lenabasum, a Selective CB2 Cannabinoid Receptor Agonist.

Background: Endocannabinoids, which are present throughout the central nervous system (CNS), can activate CB1 and CB2 receptors. CB1 and CB2 agonists exhibit broad anti-inflammatory properties, suggesting their potential to treat inflammatory diseases. However, careful evaluation of abuse potential is necessary. Methods: This study evaluated the abuse potential of lenabasum, a selective CB2 receptor agonist in participants (n=56) endorsing recreational cannabis use. Three doses of lenabasum (20, 60, and 120mg) were compared to placebo, and nabilone (3 and 6mg). The primary endpoint was the peak effect (Emax) on a bipolar Drug Liking visual analog scale (VAS). Secondary VAS and pharmacokinetic (PK) endpoints and adverse events were assessed. Results: Lenabasum was safe and well tolerated. Compared to placebo, a 20mg dose of lenabasum did not increase ratings of Drug Liking and had no distinguishable effect on other VAS endpoints. Dose-dependent increases in ratings of Drug Liking were observed with 60 and 120mg lenabasum. Drug Liking and all other VAS outcomes were greatest for nabilone 3mg and 6mg, which is a currently FDA-approved medication. Conclusions: At a target therapeutic dose (20mg), lenabasum did not elicit subjective ratings of Drug Liking. However, supratherapeutic doses of lenabasum (60 and 120mg) did elicit subjective ratings of Drug Liking compared to placebo. Although both doses of lenabasum were associated with lower ratings of Drug Liking compared to 3mg and 6mg of nabilone, suggesting that lenabasum does have abuse potential and should be used cautiously in clinical settings. Significance Statement This work provides evidence that in people with a history of recreational cannabis use, lenabasum was safe and well-tolerated, although it did demonstrate abuse potential. This work supports further development of lenabasum for potential therapeutic indications.

Are you thinking what I'm thinking? Defining what we mean by "polysubstance use."

The rise in drug overdoses and harms associated with the use of more than one substance has led to increased use of the term "polysubstance use" among researchers, clinicians, and public health officials. However, the term retains no consistent definition across contexts. The current authors convened from disciplines including sociology, epidemiology, neuroscience, and addiction psychiatry to propose a recommended definition of polysubstance use. An iterative process considered authors' formal and informal conversations, insights from relevant symposia, talks, and conferences, as well as their own research and clinical experiences to propose the current definition. Three key concepts were identified as necessary to define polysubstance use: (1) substances involved, (2) timing, and (3) intent. Substances involved include clarifying either (1) the number and type of substances used, (2) presence of more than one substance use disorder, or (3) primary and secondary substance use. The concept of timing is recommended to use clear terms such as simultaneous, sequential, and same-day polysubstance use to describe short-term behaviors (e.g., 30-day windows). Finally, the concept of intent refers to clarifying unintentional use or exposure when possible, and greater attention to motivations of polysubstance use. These three components should be clearly defined in research on polysubstance use to improve consistency across disciplines. Consistent definitions of polysubstance use can aid in the synthesis of evidence to better address an overdose crisis that increasingly involves multiple substances.

Sublingual dexmedetomidine (BXCL501) reduces opioid withdrawal symptoms: findings from a multi-site, phase 1b/2, randomized, double-blind, placebo-controlled trial.

Background: Like other alpha-2-adrenergic receptor agonists, dexmedetomidine may reduce the severity of opioid withdrawal but with fewer adverse cardiovascular effects.Objective: This study assessed the safety of sublingual dexmedetomidine (BXCL501) and its preliminary efficacy in treating opioid withdrawal (ClinicalTrials.gov: NCT04470050).Methods: Withdrawal was induced among individuals with physiological dependence on opioids via discontinuation of oral morphine (Days 1-5). Participants were randomized to receive placebo or active BXCL501: 30, 60, 90, 120, 180, and 240 µg twice daily (Days 6-12). Treatment-emergent adverse events (TEAEs) were the primary outcome measure. Secondary outcomes included the Clinical and Subjective Opiate Withdrawal Scales (COWS and SOWS-Gossop, respectively), and the Agitation and Calmness Evaluation Scale (ACES).Results: Of 225 participants enrolled, 90 discontinued during morphine stabilization. Post-BXCL501 randomization (Day 6) data were available from 135 participants (73% male), with 33% completing thru Day 12. In total, 36 subjects reported 1 or more TEAE. Higher doses of BXCL501 (i.e. 180 and 240 µg, twice daily) increased the frequency of: hypotension, orthostatic hypotension, and somnolence. TEAEs related to BXCL501 were mild or moderate in severity, except for one participant in the 120 µg condition whose orthostatic hypotension and bradycardia were classified as severe. Higher BXCL501 dose conditions (120, 180, and 240 µg) resulted in statistically significant reductions in COWS & SOWS scores. Mean ratings on the ACES were between 3 (mild), 4 (normal), and 5 (mild calmness), with few significant differences as a function of dose.Conclusions: These findings support the continued development of BXCL501 for the management of opioid withdrawal.

The effects of acute oral naltrexone pretreatment on the abuse potential of intranasal methamphetamine, and the relationship between reward/punishment sensitivity and methamphetamine's effects.

One potential medication for treating methamphetamine use disorder is the opioid antagonist naltrexone (NLTX). Despite encouraging preclinical findings, the results of clinical studies have been mixed. The primary aim of the current trial was to examine the effects of acute NLTX pretreatment on the subjective and reinforcing effects of intranasal methamphetamine. Nonmedical psychostimulant users completed outpatient testing sessions in which they received oral placebo (0 mg) or NLTX (50 mg) before intranasal methamphetamine (30 mg/70 kg). Primary outcome measures were peak positive subjective effects (e.g. drug 'Liking') assessed on a visual analog scale (0-100), and methamphetamine self-administration using an operant self-administration task. Participants also completed a probabilistic categorization task to assess reward and punishment learning sensitivity. Complete data were available from 13 male and 1 transgender (male-to-female) participant (age: 33.4 ± 7.6 years). Intranasal methamphetamine significantly increased subjective ratings of drug 'Liking', 'Good Effect' and 'High' from baseline (P's < 0.01), but did not significantly vary as a function of placebo or NLTX pretreatment. Similarly, methamphetamine self-administration did not vary between the placebo and NLTX pretreatment conditions. This sample did not demonstrate a significant 'bias' in learning from positive and negative outcomes (i.e. reward and punishment sensitivity), and reward/punishment sensitivity was not correlated with the effects of methamphetamine or the effects of NLTX on methamphetamine. The current study argues against the use of NLTX as a stand-alone medication for treating methamphetamine use disorder.

Emotional reactions of trained overdose responders who use opioids following intervention in an overdose event.

Background: Our aim was to explore emotional reactions to intervening in an overdose event from the perspective of individuals who use opioids (peer responders). In addition, we were interested in the impact this experience may have on peer responders' feelings about helping in an overdose situation in the future. Methods: For this qualitative sub-study of a randomized controlled trial (RCT), data from 61 interviews were analyzed thematically using an inductive approach. Results: Peer responders had diverse emotional reactions to the overdose event. These ranged from a sense of pride and other positive feelings associated with their ability to help to ambivalence about being involved in situations perceived as challenging and burdensome. There were few reports of the overdose event as an exclusively negative experience. Many peer responders perceived it as their duty to use naloxone again if required. However, some had ambivalent feelings toward this responsibility, which may be related to negative experiences with previous intervention efforts. Conclusions: The capacity of people who use opioids to help reduce the harms associated with opioid overdose is experienced as empowering by some. Nonetheless, engaging peer responders in strategies to reduce opioid-related mortality should be coupled with appropriate resources to process their experiences and emotional responses.

UNDERSTANDING PREFERENCES FOR TYPE OF TAKE-HOME NALOXONE DEVICE: INTERNATIONAL QUALITATIVE ANALYSIS OF THE VIEWS OF PEOPLE WHO USE OPIOIDS.

Background: Take-home naloxone (THN) is provided to non-medically trained people to reverse potential opioid overdoses. There is an increasing range of effective intramuscular (IM) and intranasal (IN) naloxone devices and this paper explores the types preferred by people who use opioids, using consumer behaviour literature to interpret the findings. Methods: Data derive from two unconnected qualitative studies involving audio-recorded semi-structured interviews. Study 1 was conducted in the United States (n=21 users of non-medical/illicit opioids). Study 2 was conducted in Australia (n=42 users of non-medical/illicit or prescribed opioids). Findings: Most participants preferred IN naloxone. Preferences were based on the ease, speed, safety and comfort of each device and underpinned by accounts of overdose revivals as being very rushed and frightening situations. Preferences related to complex interactions between the naloxone device ('product'); the knowledge, skills, experience and attitudes of the lay responder ('consumer'), and when, where and how naloxone was to be used ('usage situation'). Conclusions: THN programs should offer choice of device when possible and nasal naloxone if resources permit. Asking people which devices they prefer and why and treating them as valued consumers of naloxone products can generate insights that improve future naloxone technology and increase THN uptake and usage.

5HT-2C agonist lorcaserin decreases cannabis self-administration in daily cannabis smokers.

There are no FDA-approved treatments for cannabis use disorder (CUD). Preclinical research has shown that the 5HT-2C agonist lorcaserin attenuates cue-induced reinstatement of THC seeking and self-administration. The goal of this placebo-controlled, counterbalanced, within-subject human laboratory study was to examine lorcaserin's effects on cannabis intoxication and self-administration. Lorcaserin (10 mg BID) was administered during one of two 13-day inpatient phases and placebo during the other; each phase was separated by ≥7 days of washout. Inpatient phases comprised (1) standardized cannabis administration (7.0% THC) at no financial cost (intoxication), counterbalanced with (2) the option to self-administer cannabis following either 0 or 3 days of abstinence. Cognitive task performance, food intake, subjective ratings of drug effects, objective/subjective sleep measures, and tobacco cigarette use were also assessed. Fifteen normal-weight, daily cannabis users (4F, 11M) not seeking treatment for CUD completed the study. Lorcaserin significantly reduced cannabis self-administration following 0 and 3 days of cannabis abstinence and also reduced craving for cannabis during abstinence. Lorcaserin produced small but significant increases in positive cannabis ratings and body weight relative to placebo. Lorcaserin also reduced tobacco cigarette smoking on days of cannabis administration relative to placebo. During abstinence, subjective but not objective measures of sleep quality worsened during lorcaserin maintenance. Overall, lorcaserin's ability to decrease drug taking and cannabis craving in nontreatment-seeking cannabis users supports further investigation of 5HT-2C agonists as potential pharmacotherapies for CUD.

The Increasing Prevalence of Fentanyl: A Urinalysis-Based Study Among Individuals With Opioid Use Disorder in New York City.

BACKGROUND AND OBJECTIVES: Opioid-related overdose deaths in North America have increased drastically, partially due to the increased prevalence of illicitly manufactured fentanyl. The current study sought to assess the prevalence and intentionality of fentanyl use among individuals with opioid use disorder (OUD). METHODS: For this secondary analysis (study 1) we screened a total of 1118 urine samples from 316 participants with OUD from 2016 to 2019. Fentanyl knowledge and intentionality of use were assessed in a separate OUD sample (study 2; N = 33). RESULTS: In study 1, 34.6% of all urine samples tested positive for fentanyl. Overall, 149 (47.2%) participants provided more than or equal to one urine sample that tested fentanyl-positive, and 93 (29.4%) provided more than or equal to two fentanyl-positive samples. The number of fentanyl-positive samples, relative to the number of samples tested each year, increased by 330% from year 1 to 3. Study 2 found all participants had pre-existing knowledge that drugs may be adulterated with fentanyl, yet 67% were surprised by their own fentanyl-positive test result. DISCUSSION AND CONCLUSIONS: Like previous studies, our data indicate the high prevalence of fentanyl exposure and low perception of fentanyl-related risk among individuals with OUD, respectively, suggesting that opioid overdose harm reduction efforts may need to focus more on drug users' understanding of risks related to fentanyl use and adulteration of drugs. SCIENTIFIC SIGNIFICANCE: The current studies provide longitudinal data on fentanyl exposure prevalence and risk perception that is uniquely granular by assessing OUD treatment status, and by identifying potential associations between fentanyl exposure with the presence of other drug use and nonfatal overdose. (Am J Addict 2021;30:65-71).

Intervention in an opioid overdose event increases interest in treatment among individuals with opioid use disorder.

Background: This study sought to explore whether intervening in suspected cases of opioid overdose alters interest in treatment for opioid use disorder (OUD). Data were collected as a part of a trial comparing the effects of different overdose education and naloxone distribution (OEND) training curricula on overdose outcomes. Methods: Following OEND training, participants completed four in-person follow-up visits at 1-, 3-, 6- and 12-months. Participants were also regularly contacted to inquire about overdose events they responded to, witnessed, or experienced themselves. Other assessments included the Addiction Severity Index that queries participants' perceived importance of drug treatment on a scale of: 0 (Not at All) to 4 (Extremely). For the current secondary data analysis, treatment importance was assessed at the time points most immediately preceding and following participant intervention in an overdose event using naloxone. Results: The sample reported a mean duration of opioid use of 14.9 (± 11.5) years, with 67% having witnessed an overdose event prior to the study. Of the 321 enrolled, 92 participants used naloxone in response to 166 suspected cases of an opioid overdose. For the entire sample, mean treatment importance did not significantly change throughout the study. Among participants who utilized naloxone, treatment importance increased following the event (Before: 3.03, After: 3.39, p = 0.02). Due to the amount of time between the overdose event and assessment of post-event treatment importance (40.5 days, ±40.2), the current study most likely underestimates this effect. Conclusions: The current study suggests that responding to an overdose event increases interest in OUD treatment. Currently only considered an acute intervention to reduce overdose morbidity and mortality, OEND may have the potential to increase enrollment in medications to treat OUD. However, a prospective investigation needs to determine if the impact of an overdose event could be utilized to increase treatment engagement.

A randomized, double-blind, placebo-controlled study of the kappa opioid receptor antagonist, CERC-501, in a human laboratory model of smoking behavior.

Preclinical data indicate that selective kappa opioid receptor antagonists reduce nicotine self-administration and withdrawal symptoms. The aim of the current study was to determine whether treatment with CERC-501, an orally available, potent, and selective kappa opioid receptor antagonist, could alleviate nicotine withdrawal and craving and mitigate mood alterations associated with nicotine withdrawal in humans. Healthy, adult cigarette smokers were enrolled into this randomized, multisite, double-blind, placebo-controlled, crossover study. Participants completed two 8-day treatment phases during which they received either CERC-501 (15 mg, p.o., once daily) or placebo. On the seventh day of each dosing phase, participants were admitted as inpatients for an 18-hour cigarette abstinence period followed by experimental testing. The primary outcome measures were (a) performance on the McKee Smoking Lapse test (ie, latency to smoke in exchange for money) and (b) number of cigarettes self-administered during a 60-minute ad lib smoking period. Other outcomes included measures of craving, mood, anxiety, nicotine withdrawal, and subjective effects of cigarette smoking. A total of 71 participants who smoked an average of approximately 23 cigarettes per day were enrolled, and 56 subjects completed the study. CERC-501 was well tolerated, but it did not significantly alter the latency to start smoking (CERC-501: 16.5 min vs placebo: 17.7 min) or the number of cigarettes smoked (CERC-501: 3.3 cigarettes vs placebo: 3.1 cigarettes). Compared with placebo, CERC-501 also did not affect cigarette craving, mood, anxiety, nicotine withdrawal, or subjective effects of smoking. These findings do not support a role for CERC-501 in the treatment of nicotine use disorder.

Naloxone-Induced Withdrawal in Individuals With and Without Fentanyl-Positive Urine Samples.

BACKGROUND AND OBJECTIVE: This retrospective analysis of data from heroin users screening for clinical research, sought to determine if more naloxone is needed to precipitate opioid withdrawal among those who regularly use heroin with fentanyl, as opposed to those who use heroin without fentanyl. METHODS: Over the course of three to five screening visits, participants completed assessments of drug use, along with urine toxicology tests at each visit. To test for opioid dependence, 29 participants completed a modified Wang test (score: 0-150) during which an intramuscular dose of naloxone (0.2-0.4 mg) was administered and the severity of withdrawal was quantified. RESULTS: The severity of opioid withdrawal was compared between individuals whose urine toxicology regularly tested positive for fentanyl (N = 15), and those only positive for other opioids (N = 14). No significant differences were found in demographic or drug use between the fentanyl-positive (mean: age 41.1 years, 9.1 bags heroin/d) and fentanyl-negative (42.0 years, 10.0 bags heroin/d) groups. Intramuscular naloxone-precipitated robust withdrawal in both samples (P < .01) with no significant difference (P = .8) in the severity (fentanyl positive [100.6 ± 13.4]; fentanyl negative [82.7 ± 9.6]). CONCLUSIONS AND SCIENTIFIC SIGNIFICANCE: These data suggest that a standard naloxone dose can be equally effective at precipitating withdrawal in individuals using heroin with fentanyl compared to heroin without fentanyl. These data contribute to our understanding of how naloxone antagonizes the effects of fentanyl and may have significant implications for the clinical laboratory and opioid overdose. A prospective clinical laboratory study with the proper opioid maintenance controls is needed to provide a more definitive finding. (Am J Addict 2019;00:00-00).

Transition of Patients with Opioid Use Disorder from Buprenorphine to Extended-Release Naltrexone: A Randomized Clinical Trial Assessing Two Transition Regimens.

BACKGROUND AND OBJECTIVE: When patients seek to discontinue buprenorphine (BUP) treatment, monthly injectable extended-release naltrexone (XR-NTX) may help them avoid relapse. The efficacy of low ascending doses of oral NTX vs placebo for patients transitioning from BUP to XR-NTX is evaluated in this study. METHODS: In a phase 3, hybrid residential/outpatient study, clinically stable participants with opioid use disorder (N = 101), receiving BUP for more than or equal to 3 months and seeking antagonist treatment, were randomized (1:1) to 7 residential days of descending doses of BUP and low ascending doses of oral NTX (NTX/BUP, n = 50) or placebo (PBO-N/BUP, n = 51). Both groups received standing ancillary medications and psychoeducational counseling. Following negative naloxone challenge, participants received XR-NTX (day 8). The primary endpoint was the proportion of participants who received and tolerated XR-NTX. RESULTS: There was no statistical difference between groups for participants receiving a first dose of XR-NTX: 68.6% (NTX/BUP) vs 76.0% (PBO-N/BUP; P = .407). The mean number of days with peak Clinical Opiate Withdrawal Scale (COWS) score less than or equal to 12 during the treatment period (days 1-7) was similar for NTX/BUP and PBO-N/BUP groups (5.8 vs 6.3; P = .511). Opioid withdrawal symptoms during XR-NTX induction and post-XR-NTX observation period (days 8-11) were mild and similar between groups (mean peak COWS score: NTX/BUP, 5.1 vs PBO-N/BUP, 5.4; P = .464). Adverse events were mostly mild/moderate. CONCLUSIONS AND SCIENTIFIC SIGNIFICANCE: Low ascending doses of oral NTX did not increase induction rates onto XR-NTX compared with placebo. The overall rate of successful induction across treatment groups supports a brief BUP taper with standing ancillary medications as a well-tolerated approach for patients seeking transition from BUP to XR-NTX. (Am J Addict 2020;00:00-00).

Guanfacine decreases symptoms of cannabis withdrawal in daily cannabis smokers.

The α2a-adrenergic agonist, lofexidine, reduced cannabis withdrawal-related sleep disruption in the laboratory, but side effects (e.g. fatigue, hypotension) limit its utility as a treatment for cannabis use disorder. This study tested the potential efficacy and tolerability of a daily bedtime administration of the FDA-approved α2a-adrenergic agonist, guanfacine, in a human laboratory model of cannabis use disorder. Daily, nontreatment-seeking cannabis smokers (13M, 2F) completed a within-subject study comprising two 9-day inpatient study phases. Each phase tested the effects of daily placebo or immediate-release guanfacine (2 mg) on cannabis intoxication (5.6 percent THC; 2 days), withdrawal (4 days of abstinence) and subsequent 'relapse' (3 days of cannabis self-administration). Ratings of mood, sleep, cardiovascular effects, food intake, psychomotor performance and cannabis self-administration were assessed. An outpatient phase preceded each inpatient phase for medication clearance or dose induction. Under placebo medication conditions, cannabis abstinence produced significant withdrawal, including irritability, sleep disruption and anorexia. Guanfacine reduced ratings of irritability and improved objective measures of sleep during cannabis withdrawal relative to placebo but did not reduce cannabis self-administration. Guanfacine was well tolerated with little evidence of fatigue and only small decreases in blood pressure: no dose was held due to hypotension. Thus, a single daily administration of guanfacine at bedtime improved sleep and mood during cannabis withdrawal relative to placebo. This positive signal supports further studies varying the guanfacine dose, formulation or frequency of administration, or combining it with other medications to increase the likelihood of having an impact on cannabis use.

Varenicline and nabilone in tobacco and cannabis co-users: effects on tobacco abstinence, withdrawal and a laboratory model of cannabis relapse.

Tobacco and cannabis co-users (T+CUs) have poor cannabis cessation outcomes, but the mechanisms underlying this are not well understood. This laboratory study examined the effects of (1) the partial nicotinic agonist, varenicline, on tobacco cessation among T+CUs, and (2) varenicline, alone, and when combined with the cannabinoid agonist nabilone, on cannabis withdrawal and a laboratory model of cannabis relapse. Non-treatment-seeking T+CUs were randomized to active-varenicline or placebo-varenicline, and completed a 15-day outpatient phase; varenicline was titrated to 1 mg BID during days 1-8, and participants were instructed to abstain from tobacco during days 9-15. Participants then moved inpatient for 16 days, where they continued their outpatient medication and tobacco abstinence. Inpatient testing included two, 8-day medication periods, where active-nabilone and placebo-nabilone were administered in counterbalanced order, and measures of acute cannabis effects (days 1-2), withdrawal (days 4-5) and 'relapse' (days 6-8) were collected. Participants in the active-varenicline group were more likely to achieve cotinine-verified tobacco abstinence during the outpatient period versus placebo-varenicline group (46 percent versus 24 percent, respectively), and also reported less mood disturbance and cigarette craving while inpatient. Active-nabilone attenuated cannabis withdrawal in both groups but did not affect cannabis relapse. Regression analyses revealed that two tobacco-related variables, i.e. age of first cigarette use, and cigarette craving while inpatient, were independent predictors of cannabis relapse outcomes. Thus, varenicline holds promise in this population, as a tool to examine the effects of tobacco abstinence on cannabis use outcomes, and as a component of smoking cessation treatments targeting T+CUs.

Chronic pain and opioid abuse: Factors associated with health-related quality of life.

BACKGROUND AND OBJECTIVES: While research on the separate relationships between health-related quality of life (HRQOL) and chronic pain, and HRQOL and opioid abuse has been sparse, even less work has investigated the factors associated with HRQOL in individuals who have both chronic pain and meet criteria for opioid use disorder. The data presented in this analysis should allow a better understanding the factors important to quality of life among this dual-diagnosed population. METHODS: Individuals with dual diagnoses of chronic pain and opioid use disorder were recruited for clinical research studies at Columbia University Medical Center. Participants (n = 47) completed inventories to assess pain (Brief Pain Inventory), opioid (ab)use, and depression (Beck Depression Inventory). Variable from these and other inventories, along with demographic factors (age, race, sex, pain severity, depressive symptoms, duration of opioid use, route of opioid use, amount of opioid use) were entered into a regression analysis in order to identify the strongest predictors of SF-36 Health Survey score. RESULTS: In the bivariate analysis we found that demographic and drug use variables were rarely associated with HRQOL. Typically, ratings of pain severity and pain interference were the best predictors. In the multivariate analysis, we found that across the several HRQOL dimensions greater Brief Pain Inventory (BPI) ratings of pain "interference" and Beck Depression Inventory (BDI) scores were consistently associated with lower HRQOL. CONCLUSIONS AND SCIENTIFIC SIGNIFICANCE: These data suggest that insufficient pain management and depression are significant variables contributing to lower quality of life among individuals with chronic pain and opioid use disorder. (Am J Addict 2017;26:815-821).

Inflammatory Pain Promotes Increased Opioid Self-Administration: Role of Dysregulated Ventral Tegmental Area µ Opioid Receptors.

Pain management in opioid abusers engenders ethical and practical difficulties for clinicians, often resulting in pain mismanagement. Although chronic opioid administration may alter pain states, the presence of pain itself may alter the propensity to self-administer opioids, and previous history of drug abuse comorbid with chronic pain promotes higher rates of opioid misuse. Here, we tested the hypothesis that inflammatory pain leads to increased heroin self-administration resulting from altered mu opioid receptor (MOR) regulation of mesolimbic dopamine (DA) transmission. To this end, the complete Freund's adjuvant (CFA) model of inflammation was used to assess the neurochemical and functional changes induced by inflammatory pain on MOR-mediated mesolimbic DA transmission and on rat intravenous heroin self-administration under fixed ratio (FR) and progressive ratio (PR) schedules of reinforcement. In the presence of inflammatory pain, heroin intake under an FR schedule was increased for high, but attenuated for low, heroin doses with concomitant alterations in mesolimbic MOR function suggested by DA microdialysis. Consistent with the reduction in low dose FR heroin self-administration, inflammatory pain reduced motivation for a low dose of heroin, as measured by responding under a PR schedule of reinforcement, an effect dissociable from high heroin dose PR responding. Together, these results identify a connection between inflammatory pain and loss of MOR function in the mesolimbic dopaminergic pathway that increases intake of high doses of heroin. These findings suggest that pain-induced loss of MOR function in the mesolimbic pathway may promote opioid dose escalation and contribute to opioid abuse-associated phenotypes. SIGNIFICANCE STATEMENT: This study provides critical new insights that show that inflammatory pain alters heroin intake through a desensitization of MORs located within the VTA. These findings expand our knowledge of the interactions between inflammatory pain and opioid abuse liability, and should help to facilitate the development of novel and safer opioid-based strategies for treating chronic pain.

The effects of ibudilast, a glial activation inhibitor, on opioid withdrawal symptoms in opioid-dependent volunteers.

Glial activation is hypothesized to contribute directly to opioid withdrawal. This study investigated the dose-dependent effects of a glial cell modulator, ibudilast, on withdrawal symptoms in opioid-dependent volunteers after abrupt discontinuation of morphine administration. Non-treatment-seeking heroin-dependent volunteers (n = 31) completed the in-patient, double-blind, placebo-controlled, within-subject and between-group study. Volunteers were maintained on morphine (30 mg, QID) for 14 days and placebo (0 mg, QID) for the last 7 days of the 3-week study. Volunteers also received placebo (0 mg, PO, BID) capsules on days 1-7. On days 8-21, volunteers were randomized to receive ibudilast (20 or 40 mg, PO, BID) or placebo capsules. Subjective and clinical ratings of withdrawal symptoms were completed daily using daily using the Subjective Opioid Withdrawal Scale (SOWS) and Clinical Opioid Withdrawal Scale (COWS). Medication side effects were also monitored. Relative to the first 2 weeks, all groups exhibited withdrawal during the third week as assessed by the SOWS and COWS (P ≤ 0.0001). Although overall SOWS scores did not differ between groups, exploratory analyses pooling the two ibudilast groups demonstrated that they had lower ratings of withdrawal symptoms on SOWS items ('anxious,' 'perspiring,' 'restless,' 'stomach cramps') during detoxification relative to the placebo group. Ibudilast was well tolerated; no serious adverse events occurred during the study. Pharmacological modulation of glial activity with ibudilast decreased some subjective ratings of opioid withdrawal symptoms. These exploratory findings are the first to demonstrate the potential clinical utility of glial modulators for treating opioid withdrawal in humans.

Searching for evidence of genetic mediation of opioid withdrawal by opioid receptor gene polymorphisms.

BACKGROUND: Previous research has identified many genetic polymorphisms that appear to mediate the effects of opioid drugs. However, the relationship between genetic polymorphisms and the severity of opioid withdrawal has not yet been characterized. METHODS: Data were collected from 48 daily heroin users who previously completed a standardized abstinence-induced or naloxone-precipitated withdrawal procedure to assess opioid dependence. The total withdrawal severity score (based on the COWS) from this procedure was correlated with genotype information for variants of OPRM1 (rs1799971; rs6848893), OPRD1 (rs10753331; rs2234918; rs581111; rs678849; rs1042114), and OPRK1 (rs6473797; rs963549). Genotype and other participant variables (age, race, sex, duration of drug use, concomitant drug use, route of opioid use) were used as predictors. RESULTS: Of these variables, those individually correlated with a p < .2 were entered into a multivariate regression in order to identify the most predictive model. Three polymorphisms were significantly associated with severity of abstinence-induced withdrawal (n = 19) in the bivariate analysis (R): OPRM1 rs6848893 (.45), OPRD1 rs10753331 (.03), and rs678849 (.08), but only the OPRM1 rs6848893 was retained in the multivariate model (p < .001). For participants who underwent naloxone-precipitated withdrawal (n = 29) only OPRK1 rs6473797 (-.23) was significant in the bivariate analysis, though not retained in the final model. CONCLUSIONS: These data provide evidence for genetic modulation of opioid withdrawal severity, and suggest there may be qualitative differences between withdrawal resulting from abstinence and antagonist-precipitated withdrawal. SCIENTIFIC SIGNIFICANCE: This study demonstrates the importance and feasibility of incorporating genetic information into clinical addiction research.

The pharmacogenetics of alcohol use disorder.

BACKGROUND: Annually, the use and abuse of alcohol contributes to millions of deaths and billions of dollars in societal costs. To determine the impact of genetic variation on the susceptibility to the disorder and its response to treatment, studies have been conducted to assess the contribution of a variety of candidate genetic variants. These variants, which we review here, were chosen based upon their observed or hypothesized functional relevance to alcohol use disorder (AUD) risk or to the mechanism by which medications used to treat the disorder exert their effects. METHODS: This qualitative review examines studies in which candidate polymorphisms were tested as moderator variables to identify pharmacogenetic effects on either the subjective response to alcohol or the outcomes of pharmacotherapy. RESULTS: Although findings from these studies provide evidence of a number of clinically relevant pharmacogenetic effects, the literature is limited and there are conflicting findings that require resolution. CONCLUSIONS: Pharmacogenetic studies of AUD treatment that use greater methodological rigor and better statistical controls, such as corrections for multiple testing, may help to resolve inconsistent findings. These procedures could also lead to the discovery of more robust and clinically meaningful moderator effects. As the field evolves through methodological standardization and the use of larger study samples, pharmacogenetic research has the potential to inform clinical care by enhancing therapeutic effects and personalizing treatments. These efforts may also provide insights into the mechanisms by which medications reduce heavy drinking or promote abstinence in patients with an AUD.

Abuse potential of intranasal buprenorphine versus buprenorphine/naloxone in buprenorphine-maintained heroin users.

In spite of the clinical utility of buprenorphine, parenteral abuse of this medication has been reported in several laboratory investigations and in the real world. Studies have demonstrated lower abuse liability of the buprenorphine/naloxone combination relative to buprenorphine alone. However, clinical research has not yet examined the utility of the combined formulation to deter intranasal use in a buprenorphine-maintained population. Heroin-using volunteers (n = 12) lived in the hospital for 8-9 weeks and were maintained on each of three sublingual buprenorphine doses (2, 8, 24 mg). Under each maintenance dose, participants completed laboratory sessions during which the reinforcing and subjective effects of intranasal doses of buprenorphine (8, 16 mg), buprenorphine/naloxone (8/2, 8/8, 8/16, 16/4 mg) and controls (placebo, heroin 100 mg, naloxone 4 mg) were assessed. Intranasal buprenorphine alone typically produced increases in positive subjective effects and the 8 mg dose was self-administered above the level of placebo. The addition of naloxone dose dependently reduced positive subjective effects and increased aversive effects. No buprenorphine/naloxone combination dose was self-administered significantly more than placebo. These data suggest that within a buprenorphine-dependent population, intranasal buprenorphine/naloxone has reduced abuse potential in comparison to buprenorphine alone. These data strongly argue in favor of buprenorphine/naloxone rather than buprenorphine alone as the more reasonable option for managing the risk of buprenorphine misuse.