Individual differences in the subjective response to smoked cocaine in humans

Emerging drugs for the treatment of cocaine use disorder: a review of neurobiological targets and pharmacotherapy

INTRODUCTION

Cocaine use is a global public health concern of significant magnitude, negatively impacting both the individual as well as larger society. Despite numerous trials, the discovery of an effective medication for treatment of cocaine use disorder remains elusive.

AREAS COVERED

This article reviews the emerging pharmacotherapies for treatment of cocaine use disorder, focusing on those medications that are currently in Phase II or III human clinical trials. Articles reviewed were obtained through searches of PubMed, Ovid MEDLINE, Clinicaltrials.gov and the Pharmaprojects database.

EXPERT OPINION

Research into cocaine pharmacotherapy must continue to show innovation. Given that medications targeting single neurotransmitter systems have demonstrated little efficacy in treatment of cocaine use disorder, the recent focus on pharmacotherapeutic agents with multiple neurobiochemical targets represents an exciting shift in trial design and approach. Additionally, consideration of pharmacogenetics may be helpful in identification of subpopulations of cocaine-dependent individuals who may preferentially respond to medications.

Individual predictors of the subjective effects of intravenous cocaine

The subjective and reinforcing effects of addictive substances can vary greatly between individuals. This study compared the relative contributions of baseline drug use, craving, stressful life events, and social factors in determining the subjective effects of cocaine in individual participants. Twelve veterans meeting criteria for cocaine dependence were evaluated in a laboratory setting. Self-report of the subjective effects of intravenous cocaine was recorded following single- and double-blind, placebo-controlled injections. Increased positive subjective effects of cocaine, including drug-induced 'good' effects and the value of intravenous injections, were most strongly correlated with greater family and social dysfunction measured through the Addiction Severity Index (ASI). Social dysfunction was the strongest predictor of cocaine-induced euphoria, accounting for approximately one-half of its variability. Participants who were dissatisfied with their current marital status reported almost no 'bad' effects of cocaine but instead reported increased drug-induced 'high', euphoria, and injection value. Although further research is required to determine the generalizability of this association, our findings are parallel to recent preclinical results showing that social interaction can attenuate psychostimulant reward. Effects of substance abuse treatment that rely on improved social function may be mediated through changes in the brain's reinforcement system that modify the rewarding effects of cocaine.

The subjective effects of cocaine: relationship to years of cocaine use and current age

BACKGROUND

Little is known about whether the duration of cocaine use or an individual's age may influence the acute effects of cocaine, patterns of use, and specific treatment needs.

OBJECTIVES

This post hoc analysis determined whether the duration of cocaine use or current age influenced the acute subjective response to cocaine. Data from four smoked cocaine self-administration laboratory studies were combined and analyzed to determine whether the subjective effects of a 25-mg smoked cocaine dose varied as a function of years of cocaine use or current age.

METHODS

Thirty-six nontreatment-seeking healthy cocaine users (ages 32-49) were admitted to studies lasting from 12 to 105 days. Participants rated the subjective effects of each cocaine dose from 0 to 100 by completing a computerized self-report visual analogue scale (VAS). The main outcome measures were the change in VAS ratings between a baseline placebo dose and the first 25-mg dose of smoked cocaine.

RESULTS

No significant relationship was found between the subjective effects of cocaine and years of cocaine use (mean 20.9, range 5-30) or current age (mean 41.1, range 32-49).

CONCLUSION

Among long-term cocaine users between the ages of 32 and 49, the acute subjective effects of cocaine did not vary as a function of years of cocaine use or current age.

SCIENTIFIC SIGNIFICANCE

These data fail to support the incentive sensitization theory for addiction by Robinson and Berridge, as cocaine "liking" and "wanting" remained the same regardless of age or years of cocaine use.

Caffeine choice prospectively predicts positive subjective effects of caffeine and d-amphetamine

BACKGROUND

Individuals vary in their subjective and behavioral response to psychomotor stimulants and these differences may be associated with the likelihood of developing problematic use of these drugs. The present study sought to determine whether individual differences in caffeine choice prospectively predict subjective response to acute doses of caffeine and d-amphetamine.

METHODS

In Phase 1, Choosers and Nonchoosers of caffeine were identified using 10 independent choice trials in which subjects repeatedly chose between caffeine (200mg/70 kg) and placebo. Choosers were defined as those who chose caffeine over placebo on ≥7 of the 10 trials; Nonchoosers were those who chose placebo on ≥7 trials. In Phase 2, Choosers and Nonchoosers were compared in their subjective response to caffeine (100, 200, 400mg/70 kg) and d-amphetamine (5, 10, 20 mg/70 kg).

RESULTS

Of the 22 participants completing the study, 11 met criteria for being a caffeine Chooser and 8 were Nonchoosers. In Phase 1, Choosers reported higher ratings of positive (i.e., pleasant) and lower ratings of negative (i.e., unpleasant) effects of caffeine during the sampling sessions. In Phase 2, caffeine Choosers reported more positive subjective effects and fewer negative effects of caffeine and d-amphetamine, particularly at the highest doses examined.

CONCLUSIONS

Individual differences in caffeine reinforcement predicted subsequent subjective response to both d-amphetamine and caffeine. This observation may have clinical utility for identifying individuals who are vulnerable to the reinforcing effects of abused psychomotor stimulants.

Cocaine is low on the value ladder of rats: possible evidence for resilience to addiction

Background

Assessing the relative value of cocaine and how it changes with chronic drug use represents a long-standing goal in addiction research. Surprisingly, recent experiments in rats – by far the most frequently used animal model in this field – suggest that the value of cocaine is lower than previously thought.

Methodology/Principal Findings

Here we report a series of choice experiments that better define the relative position of cocaine on the value ladder of rats (i.e., preference rank-ordering of different rewards). Rats were allowed to choose either taking cocaine or drinking water sweetened with saccharin – a nondrug alternative that is not biologically essential. By systematically varying the cost and concentration of sweet water, we found that cocaine is low on the value ladder of the large majority of rats, near the lowest concentrations of sweet water. In addition, a retrospective analysis of all experiments over the past 5 years revealed that no matter how heavy was past cocaine use most rats readily give up cocaine use in favor of the nondrug alternative. Only a minority, fewer than 15% at the heaviest level of past cocaine use, continued to take cocaine, even when hungry and offered a natural sugar that could relieve their need of calories.

Conclusions/Significance

This pattern of results (cocaine abstinence in most rats; cocaine preference in few rats) maps well onto the epidemiology of human cocaine addiction and suggests that only a minority of rats would be vulnerable to cocaine addiction while the large majority would be resilient despite extensive drug use. Resilience to drug addiction has long been suspected in humans but could not be firmly established, mostly because it is difficult to control retrospectively for differences in drug self-exposure and/or availability in human drug users. This conclusion has important implications for preclinical research on the neurobiology of cocaine addiction and for future medication development.

Similar discriminative-stimulus effects of D-amphetamine in women and men

The results of controlled non-human animal and human laboratory studies are mixed regarding whether women and men respond differently to stimulant drugs. In order to assess potential gender differences in the effects of D-amphetamine, we conducted a retrospective analysis of six studies conducted in our laboratory that used identical procedures and measures. Thirteen women and fourteen men learned to discriminate 15 mg oral D-amphetamine. After acquiring the discrimination (i.e., >or=80% correct responding on 4 consecutive sessions), the effects of a range of doses of D-amphetamine (0, 2.5, 5, 10, and 15 mg) alone and in combination with other drugs, were assessed. Only data from sessions in which D-amphetamine was administered alone were included in this analysis. D-amphetamine functioned as a discriminative stimulus and dose-dependently increased drug-appropriate responding. Women and men did not differ in their ability to discriminate D-amphetamine. Women and men differed on participant-ratings of high (women<men), nausea (women>men) and sluggish (women<men), women also experienced greater increases in diastolic pressure than men. Because the results of this study may have been confounded by the training procedures, future research should use other behavioral arrangements (e.g. drug self-administration) to determine if women and men respond differently to the effects of D-amphetamine.

Intranasal cocaine in humans: effects of sex and menstrual cycle

Studies have shown that smoked and intravenous cocaine's effects differ in cocaine-dependent women compared to men and across the menstrual cycle. However, this has not been systematically investigated with intranasal cocaine. Thus, a range of intranasal cocaine doses was examined in cocaine-dependent women across the menstrual cycle. Female cocaine users were admitted to the hospital once during the luteal phase and once during the follicular phase of their menstrual cycle; menstrual cycle phase during admissions was counterbalanced. During each admission, an intranasal cocaine dose-response curve (0.06, 0.34, 0.69 and 1.37 mg/kg) was determined during four laboratory sessions. Cocaine produced similar dose-related increases in ratings of "positive" subjective effects, cardiovascular effects and cocaine plasma levels in women in both menstrual cycle phases. To assess sex differences in the effects of intranasal cocaine, the current data were compared to published data collected in men using an identical procedure. Cocaine produced similar dose-related increases in ratings of positive subjective effects, cardiovascular effects and cocaine plasma levels in men and women. Thus, in contrast to studies examining smoked or intravenous cocaine administration, there were no sex differences or menstrual cycle effects on the subjective or cardiovascular response to intranasal cocaine, suggesting that the influence of sex and menstrual cycle on cocaine's effects vary as a function of route of administration.

Irritability following abstinence from cocaine predicts euphoric effects of cocaine administration

This study evaluated the association between negative affective symptoms during initial abstinence and euphorigenic response to experimentally administered cocaine. Cocaine-dependent individuals achieved 5 days of abstinence in a hospital setting. Forty milligrams of cocaine was given intravenously on the fifth day of abstinence, and participants were asked to rate the subjective effects produced by the drug. The associations between irritability, self-reported depression, and the subjective "high" produced by cocaine were evaluated. Increased levels of irritability and depression both correlated positively and statistically significantly with heightened response to experimentally administered cocaine as indexed by self-reported subjective "high." The positive association between irritability and subjective "high" remained after controlling for self-reported depressive symptoms. The opponent process model predicts that increased levels of negative affect should be associated with diminished euphoric response to cocaine; however, the opposite was observed. If these findings are replicated in a larger sample, then it may be necessary to reconsider the applicability of the opponent process model to cocaine addiction in humans.

The prevalence and correlates of depressive symptomatology among a community sample of crack-cocaine smokers

Depression has been identified as a disorder of clinical significance among cocaine users. Even so, its prevalence in cocaine-abusing populations is uncertain. This research employed a cross-sectional design to determine the prevalence of current depressive symptomatology among a sample of 430 not-in-treatment crack-cocaine users. Depression was assessed with the Beck Depression Inventory (BDI). The mean BDI score was 19.1. Overall, 80% of the sample had BDI scores that suggested more than minimal depression, and 55% had symptoms of moderate to severe depression. The results of a cumulative logistic regression analysis showed that men, African-Americans, and individuals with some college education were less likely to be depressed. Individuals with higher Addiction Severity Index composite scores for family/social, medical, legal, and alcohol problems had a greater likelihood of reporting symptoms of depression. Frequency of cocaine use and perceived need for treatment were also positively associated with higher BDI scores. The results suggest that the prevalence of depression among crack users is higher than has been previously reported. Treatment programs should routinely screen crack-cocaine users for depression. The BDI may be a suitable tool for such efforts since it has an acceptable level of internal consistency when employed with crack users (a = 0.89).

Depressive symptoms modulate the subjective and physiological response to cocaine in humans

The goal of this study was to examine the relationship between the presence of subclinical depressive symptoms and physiological and subjective responses to smoked cocaine in humans. Cocaine users without major depression, who participated in various inpatient studies, received a single 0.4 mg/kg of smoked cocaine. When the relationship between the Beck Depression Inventory (BDI) scores and various subjective and physiological responses to cocaine was examined, similar trends were found. Low BDI scores of 0-7 were associated with a smaller physiological and subjective cocaine response. In contrast, BDI ranges of 8-13 were associated with enhanced cocaine response which plateaued or declined in the higher (> 14) BDI group. These group differences were not explained by sex or body weight differences among groups. The implication of these results is that the presence of depressive symptoms may affect cocaine use behavior partly by being associated with an enhanced response to cocaine.