Pronounced paranoia as a result of cocaine-disulfiram interaction: case report and mode of action

Treatment-refractory substance use disorder: Focus on alcohol, opioids, and cocaine

Substance use disorders are common, but only a small minority of patients receive adequate treatment. Although psychosocial therapies are effective, relapse is common. This review focusses on novel pharmacological and other treatments for patients with alcohol, opioid, or cocaine use disorders who do not respond to conventional treatments. Disulfiram, acamprosate, and the opioid antagonist naltrexone have been approved for the treatment of alcoholism. A novel, "as needed" approach is the use of the mu-opioid antagonist and partial kappa agonist nalmefene to reduce alcohol consumption. Other novel pharmacological approaches include the GABA-B receptor agonist baclofen, anticonvulsants such as topiramate and gabapentin, the partial nicotine receptor agonist varenicline, and other drugs. For opioid dependence, opioid agonist therapy with methadone or buprenorphine is the first-line treatment option. Other options include oral or depot naltrexone, morphine sulfate, depot or implant formulations, and heroin (diacetylmorphine) in treatment-refractory patients. To date, no pharmacological treatment has been approved for cocaine addiction; however, 3 potential pharmacological treatments are being studied, disulfiram, methylphenidate, and modafinil. Pharmacogenetic approaches may help to optimize treatment response in otherwise treatment-refractory patients and to identify which patients are more likely to respond to treatment, and neuromodulation techniques such as repeated transcranial magnetic stimulation and deep brain stimulation also may play a role in the treatment of substance use disorders. Although no magic bullet is in sight for treatment-refractory patients, some novel medications and brain stimulation techniques have the potential to enrich treatment options at least for some patients.

Psychotic Symptoms Associated with the use of Dopaminergic Drugs, in Patients with Cocaine Dependence or Abuse

BACKGROUND

In the field of dual diagnosis, physicians are frequently presented with pharmacological questions. Questions about the risk of developing psychotic symptoms in cocaine users who need treatment with dopaminergic drugs could lead to an undertreatment.

OBJECTIVE

Review the presence of psychotic symptoms in patients with cocaine abuse/dependence, in treatment with dopaminergic drugs.

METHODS

Systematic PubMed searches were conducted including December 2014, using the keywords: "cocaine", dopaminergic drug ("disulfuram-methylphenidate-bupropion-bromocriptine-sibutramineapomorphine- caffeine") and ("psychosis-psychotic symptoms-delusional-paranoia"). Articles in English, Spanish, Portuguese, French, and Italian were included. Articles in which there was no history of cocaine abuse/dependence, absence of psychotic symptoms, systematic reviews, and animal studies, were excluded.

RESULTS

313 papers were reviewed. 7 articles fulfilled the inclusion-exclusion criteria. There is a clinical trial including 8 cocaine-dependent patients using disulfiram in which 3 of them presented psychotic symptoms and 6 case-reports: disulfuram (1), methylphenidate (1), disulfiram with methylphenidate (2), and bupropion (2), reporting psychotic symptoms, especially delusions of reference and persecutory ideation.

CONCLUSION

Few cases have been described, which suggests that the appearance of these symptoms is infrequent. The synergy of dopaminergic effects or the dopaminergic sensitization in chronic consumption are the explanatory theories proposed by the authors. In these cases, a relationship was found between taking these drugs and the appearance of psychotic symptoms. Given the low number of studies found, further research is required. The risk of psychotic symptoms seems to be acceptable if we compare it with the benefits for the patients but a closer monitoring seems to be advisable.

Chronic loss of noradrenergic tone produces β-arrestin2-mediated cocaine hypersensitivity and alters cellular D2 responses in the nucleus accumbens

Cocaine blocks plasma membrane monoamine transporters and increases extracellular levels of dopamine (DA), norepinephrine (NE) and serotonin (5-HT). The addictive properties of cocaine are mediated primarily by DA, while NE and 5-HT play modulatory roles. Chronic inhibition of dopamine β-hydroxylase (DBH), which converts DA to NE, increases the aversive effects of cocaine and reduces cocaine use in humans, and produces behavioral hypersensitivity to cocaine and D2 agonism in rodents, but the underlying mechanism is unknown. We found a decrease in β-arrestin2 (βArr2) in the nucleus accumbens (NAc) following chronic genetic or pharmacological DBH inhibition, and overexpression of βArr2 in the NAc normalized cocaine-induced locomotion in DBH knockout (Dbh -/-) mice. The D2/3 agonist quinpirole decreased excitability in NAc medium spiny neurons (MSNs) from control, but not Dbh -/- animals, where instead there was a trend for an excitatory effect. The Gαi inhibitor NF023 abolished the quinpirole-induced decrease in excitability in control MSNs, but had no effect in Dbh -/- MSNs, whereas the Gαs inhibitor NF449 restored the ability of quinpirole to decrease excitability in Dbh -/- MSNs, but had no effect in control MSNs. These results suggest that chronic loss of noradrenergic tone alters behavioral responses to cocaine via decreases in βArr2 and cellular responses to D2/D3 activation, potentially via changes in D2-like receptor G-protein coupling in NAc MSNs.

Elevated dopamine in the medial prefrontal cortex suppresses cocaine seeking via D1 receptor overstimulation

Previous investigations indicate that the dopamine-β-hydroxylase (DBH) inhibitors disulfiram and nepicastat suppress cocaine-primed reinstatement of cocaine self-administration behaviour. Moreover, both inhibitors increase dopamine release in the rat medial prefrontal cortex (mPFC) and markedly potentiate cocaine-induced dopamine release in this region. This study was aimed to clarify if the suppressant effect of DBH inhibitors on cocaine reinstatement was mediated by the high extracellular dopamine in the rat mPFC leading to a supra-maximal stimulation of D1 receptors in the dorsal division of mPFC, an area critical for reinstatement of cocaine-seeking behaviour. In line with previous microdialysis studies in drug-naïve animals, both DBH inhibitors potentiated cocaine-induced dopamine release in the mPFC, in the same animals in which they also suppressed reinstatement of cocaine seeking. Similar to the DBH inhibitors, L-DOPA potentiated cocaine-induced dopamine release in the mPFC and suppressed cocaine-induced reinstatement of cocaine-seeking behaviour. The bilateral microinfusion of the D1 receptor antagonist SCH 23390 into the dorsal mPFC not only prevented cocaine-induced reinstatement of cocaine seeking but also reverted both disulfiram- and L-DOPA-induced suppression of reinstatement. Moreover, the bilateral microinfusion of the D1 receptor agonist chloro-APB (SKF 82958) into the dorsal mPFC markedly attenuated cocaine-induced reinstatement of cocaine seeking. These results suggest that stimulation of D1 receptors in the dorsal mPFC plays a crucial role in cocaine-induced reinstatement of cocaine seeking, whereas the suppressant effect of DBH inhibitors and L-DOPA on drug-induced reinstatement is mediated by a supra-maximal stimulation of D1 receptors leading to their inactivation.

Selective inhibition of dopamine-beta-hydroxylase enhances dopamine release from noradrenergic terminals in the medial prefrontal cortex

INTRODUCTION

Disulfiram has been claimed to be useful in cocaine addiction therapy, its efficacy being attributed to dopamine-beta-hydroxylase (DBH) inhibition. Our previous results indicate that disulfiram and the selective DBH inhibitor nepicastat increase extracellular dopamine (DA) in the rat medial prefrontal cortex (mPFC), and markedly potentiated cocaine-induced increase. Concomitantly, in rats with cocaine self-administration history, cocaine-seeking behavior induced by drug priming was prevented, probably through overstimulation of D1 receptors due to the DA increase. The present research was aimed at studying the neurochemical mechanisms originating the enhanced DA release.

METHODS

Noradrenergic system ablation was attained by intracerebroventricular (i.c.v.) administration of the neurotoxin anti-DBH-saporin (aDBH-sap). DA, noradrenaline (NA), and DOPAC were assessed by HPLC after ex vivo tissue extraction or in vivo microdialysis. Control and denervated rats were subjected to microdialysis in the mPFC and caudate nucleus to evaluate the effect of nepicastat-cocaine combination on extracellular DA levels and their regulation by α2-adrenoceptors.

RESULTS

Fifteen days after neurotoxin or its vehicle administration, tissue and extracellular NA were reduced to less than 2% the control value, while extracellular DA was increased by approximately 100%. In control rats, nepicastat given alone and in combination with cocaine increased extracellular DA by about 250% and 1100%, respectively. In denervated rats, nepicastat slightly affected extracellular DA, while in combination with cocaine increased extracellular DA by 250%. No differences were found in the caudate nucleus. Clonidine almost totally reversed the extracellular DA elevation produced by nepicastat-cocaine combination, while it was ineffective in denervated rats.

CONCLUSIONS

This research shows that the increase of extracellular DA produced by nepicastat alone or in combination with cocaine was prevented by noradrenergic denervation. The results indicate that nepicastat enhances DA release from noradrenergic terminals supposedly by removing NA from α2-autoreceptors. In addition to the inhibition of DA uptake, the latter mechanism may explain the synergistic effect of cocaine on nepicastat-induced DA release.

An international perspective and review of cocaine-induced psychosis: a call to action

Cocaine use can induce transient psychotic symptoms that include suspiciousness, paranoia, hallucinations, and other cocaine-related behaviors. In this commentary, the authors provide an international perspective while reviewing the recent advances in epidemiology, clinical features, and risk factors related to cocaine-induced psychosis exhibited by patients with cocaine use disorders. In some settings, the occurrence of cocaine-induced psychosis has been shown to be as high as 86.5%. Many risk factors have been linked with cocaine-induced psychosis, including the quantity of cocaine consumed, lifetime amount of cocaine use, onset of cocaine dependence, years of use, routes of administration, other substance use disorder comorbidity, weight, gender, comorbidity with other medical and mental health disorders, genetics, and pharmacological interactions. Research has shown that the evaluation of cocaine-induced psychosis in patients with cocaine use is clinically relevant, especially in those patients who consume high amounts of cocaine, have a cannabis dependence history, have antisocial personality disorder, use administration routes other than intranasal, or exhibit attention-deficit/hyperactivity disorder (ADHD) comorbidity. Currently, the literature lacks information regarding the evolution of cocaine dependence or cocaine-dependent patients' risk for developing schizophrenia or other psychotic disorders. Furthermore, clinicians still do not have an evidence-based pharmacological approach to management of cocaine dependence available to them. Additional research is also needed regarding risk factors such as neurobiological markers and personality traits. Finally, we recommend the development of an integrative model including all of the risk factors and protective factors for cocaine-induced psychosis.

Neuronal copper homeostasis susceptibility by genetic defects in dysbindin, a schizophrenia susceptibility factor

Environmental factors and susceptible genomes interact to determine the risk of neurodevelopmental disorders. Although few genes and environmental factors have been linked, the intervening cellular and molecular mechanisms connecting a disorder susceptibility gene with environmental factors remain mostly unexplored. Here we focus on the schizophrenia susceptibility gene DTNBP1 and its product dysbindin, a subunit of the BLOC-1 complex, and describe a neuronal pathway modulating copper metabolism via ATP7A. Mutations in ATP7A result in Menkes disease, a disorder of copper metabolism. Dysbindin/BLOC-1 and ATP7A genetically and biochemically interact. Furthermore, disruption of this pathway causes alteration in the transcriptional profile of copper-regulatory and dependent factors in the hippocampus of dysbindin/BLOC-1-null mice. Dysbindin/BLOC-1 loss-of-function alleles do not affect cell and tissue copper content, yet they alter the susceptibility to toxic copper challenges in both mammalian cells and Drosophila. Our results demonstrate that perturbations downstream of the schizophrenia susceptibility gene DTNBP1 confer susceptibility to copper, a metal that in excess is a neurotoxin and whose depletion constitutes a micronutrient deficiency.

Evaluation of the dopamine β-hydroxylase (DβH) inhibitor nepicastat in participants who meet criteria for cocaine use disorder

In the present study, we tested the hypothesis that the potent and selective dopamine-β-hydroxylase (DβH) inhibitor nepicastat would have minimal effects on cardiovascular and pharmacokinetic parameters associated with cocaine administration and would reduce the positive subjective effects produced by cocaine. We conducted a double-blind, placebo-controlled, inpatient study of oral nepicastat (0, 80 and 160mg) concurrent with intravenous (IV) cocaine (0, 10, 20 and 40mg) in non-treatment seeking participants who metcriteria for cocaine use disorder. Safety analyses revealed that nepicastat was well-tolerated and there were no differences in adverse events observed after nepicastat plus cocaine vs. cocaine alone. In addition, the pharmacokinetic properties of cocaine administration were not altered by nepicastat treatment. Cocaine-induced cardiovascular and subjective effects were evaluated for completers in the cohort randomized to nepicastat (n=13) using a within-subjects statistical analysis strategy. Specifically, the cardiovascular and subjective effects of cocaine were assessed in the presence of placebo (0mg), 80mg of nepicastat or 160mg of nepicastat on study Days 4, 8 and 12, respectively. Analyses revealed a main effect of nepicastat to reduce several cocaine-induced positive subjective effects. Taken together, these data indicate that nepicastat is safe when co-administered with cocaine and may suppress its positive subjective effects, and may be viable as a pharmacotherapy for treatment of cocaine use disorder.

The dopamine beta-hydroxylase inhibitor nepicastat increases dopamine release and potentiates psychostimulant-induced dopamine release in the prefrontal cortex

The dopamine-beta-hydroxylase inhibitor nepicastat has been shown to reproduce disulfiram ability to suppress the reinstatement of cocaine seeking after extinction in rats. To clarify its mechanism of action, we examined the effect of nepicastat, given alone or in association with cocaine or amphetamine, on catecholamine release in the medial prefrontal cortex and the nucleus accumbens, two key regions involved in the reinforcing and motivational effects of cocaine and in the reinstatement of cocaine seeking. Nepicastat effect on catecholamines was evaluated by microdialysis in freely moving rats. Nepicastat reduced noradrenaline release both in the medial prefrontal cortex and in the nucleus accumbens, and increased dopamine release in the medial prefrontal cortex but not in the nucleus accumbens. Moreover, nepicastat markedly potentiated cocaine- and amphetamine-induced extracellular dopamine accumulation in the medial prefrontal cortex but not in the nucleus accumbens. Extracellular dopamine accumulation produced by nepicastat alone or by its combination with cocaine or amphetamine was suppressed by the α2 -adrenoceptor agonist clonidine. It is suggested that nepicastat, by suppressing noradrenaline synthesis and release, eliminated the α2 -adrenoceptor mediated inhibitory mechanism that constrains dopamine release and cocaine- and amphetamine-induced dopamine release from noradrenaline or dopamine terminals in the medial prefrontal cortex.

Randomized clinical trial of disulfiram for cocaine dependence or abuse during buprenorphine treatment

BACKGROUND

Disulfiram may be efficacious for treating cocaine dependence or abuse, possibly through inhibiting dopamine β-hydroxylase (DβH). Consequently, this randomized, placebo-controlled clinical trial of disulfiram during buprenorphine maintenance treatment evaluated the study hypothesis that disulfiram is superior to placebo and explored whether disulfiram response is greatest for participants with a single nucleotide polymorphism coding for genetically low DβH (T-allele carriers).

METHODS

We randomized 177 buprenorphine-treated opioid dependent participants with cocaine dependence or abuse to 12 weeks of double-blind treatment with disulfiram 250mg daily (n=91) or placebo (n=86). Of 155 participants genotyped, 84 were CC-homozygous, and 71 CT or TT genotypes. Primary outcomes included days per week cocaine use, number of cocaine-negative urine tests, and maximum consecutive weeks of cocaine abstinence. We analyzed an intention-to-treat comparison between disulfiram and placebo. We also explored potential pharmacogenetic interactions and examined treatment responses of four participant groups based on medication (disulfiram or placebo) by genotype (CC-homozygous or T-allele carrier) classification.

RESULTS

Disulfiram participants reported significantly less frequent cocaine use; the differences in cocaine-negative urine tests or consecutive weeks abstinence were not significant. Frequency of cocaine use was lowest in disulfiram-treated T-allele carriers; differences in cocaine-negative urine tests or consecutive weeks abstinence were not significant among the four medication-genotype groups.

CONCLUSIONS

The findings provide limited support for the efficacy of disulfiram for reducing cocaine use and suggest that its mechanism of action may involve inhibition of DβH. Further studies of its efficacy, mechanism of action, and pharmacogenetics of response are warranted.

Dopamine β-hydroxylase inhibitors enhance the discriminative stimulus effects of cocaine in rats

Inhibitors of dopamine β-hydroxylase (DBH), the enzyme that converts dopamine (DA) to norepinephrine (NE) in noradrenergic cells, have shown promise for the treatment of cocaine abuse disorders. However, the mechanisms underlying the beneficial effects of these compounds have not been fully elucidated. We used the drug discrimination paradigm to determine the impact of DBH inhibitors on the interoceptive stimulus properties of cocaine. Sprague-Dawley rats were trained to discriminate cocaine (5.6 mg/kg) from saline using a multicomponent, food-reinforced discrimination procedure. On test days, subjects were pretreated with the nonselective DBH inhibitor disulfiram (0-100.0 mg/kg i.p.) or the selective DBH inhibitor nepicastat (0-56.0 mg/kg i.p.) 2 hours prior to a test session either alone or in combination with cumulatively administered cocaine (0-5.6 mg/kg i.p.). Neither disulfiram nor nepicastat substituted for the cocaine stimulus when tested up to doses that nonspecifically reduced responding. However, in combination studies, pretreatment with either disulfiram or nepicastat produced leftward shifts in the cocaine dose-response function and also conferred cocaine-like stimulus effects to the selective NE transporter inhibitor, reboxetine (0.3-5.6 mg/kg i.p.). These results indicate that pharmacological inhibition of DBH does not produce cocaine-like interoceptive stimulus effects alone, but functionally enhances the interoceptive stimulus effects of cocaine, possibly due to facilitated increases in DA released from noradrenergic terminals. These findings suggest that DBH inhibitors have low abuse liability and provide support to clinical reports that some subjective effects produced by cocaine, particularly aversive effects, are enhanced after DBH inhibition.

Chronic inhibition of dopamine β-hydroxylase facilitates behavioral responses to cocaine in mice

The anti-alcoholism medication, disulfiram (Antabuse), decreases cocaine use in humans regardless of concurrent alcohol consumption and facilitates cocaine sensitization in rats, but the functional targets are unknown. Disulfiram inhibits dopamine β-hydroxylase (DBH), the enzyme that converts dopamine (DA) to norepinephrine (NE) in noradrenergic neurons. The goal of this study was to test the effects of chronic genetic or pharmacological DBH inhibition on behavioral responses to cocaine using DBH knockout (Dbh −/−) mice, disulfiram, and the selective DBH inhibitor, nepicastat. Locomotor activity was measured in control (Dbh +/−) and Dbh −/− mice during a 5 day regimen of saline+saline, disulfiram+saline, nepicastat+saline, saline+cocaine, disulfiram+cocaine, or nepicastat+cocaine. After a 10 day withdrawal period, all groups were administered cocaine, and locomotor activity and stereotypy were measured. Drug-naïve Dbh −/− mice were hypersensitive to cocaine-induced locomotion and resembled cocaine-sensitized Dbh +/− mice. Chronic disulfiram administration facilitated cocaine-induced locomotion in some mice and induced stereotypy in others during the development of sensitization, while cocaine-induced stereotypy was evident in all nepicastat-treated mice. Cocaine-induced stereotypy was profoundly increased in the disulfiram+cocaine, nepicastat+cocaine, and nepicastat+saline groups upon cocaine challenge after withdrawal in Dbh +/− mice. Disulfiram or nepicastat treatment had no effect on behavioral responses to cocaine in Dbh −/− mice. These results demonstrate that chronic DBH inhibition facilitates behavioral responses to cocaine, although different methods of inhibition (genetic vs. non-selective inhibitor vs. selective inhibitor) enhance qualitatively different cocaine-induced behaviors.

Psychosis induced by the interaction between disulfiram and methylphenidate may be dose dependent

There are few studies describing psychiatric symptoms occurring when methylphenidate and disulfiram are used together. The authors report a case of disulfiram and methylphenidate interaction in which psychotic symptoms could be dose dependent. The patient, diagnosed of alcohol and cocaine dependence and attention deficit hyperactivity disorder (ADHD), started treatment with methylphenidate increasing doses and disulfiram 250 mg/day over 4 weeks. During the first 2 weeks at doses of 36 mg/day of methylphenidate and maintaining disulfiram, side effects were not observed. However, by increasing to 54 mg/day, psychotic symptoms were detected. The authors reported that the effects are dose dependent. This is the first report about dose-dependent side effects in substance use disorder with ADHD.

A double-blind, placebo-controlled assessment of the safety of potential interactions between intravenous cocaine, ethanol, and oral disulfiram

BACKGROUND

A majority of cocaine addicts have a comorbid alcohol use disorder. Previous studies demonstrated efficacy of disulfiram in the treatment of cocaine dependence among patients with comorbid alcohol use disorder or opioid dependence. However, the cardiac risks of a disulfiram-ethanol reaction (DER) in individuals who drink, when coupled with the cardiac effects of cocaine, could result in significant toxicity or lethality due to the 3-way drug interaction.

AIMS

This study examined the safety of combining cocaine (30 mg i.v.) and ethanol (0.4 g/kg i.v.) in disulfiram-treated (0, 250, and 500 mg/d, p.o.) cocaine-dependent research volunteers.

RESULTS

The results showed that disulfiram did not enhance the cardiovascular effects of cocaine and may have reduced the subjective high from cocaine. In contrast, ethanol produced adverse ECG changes including QTc prolongation and a DER consisting of hypotension, tachycardia, nausea, and flushing in disulfiram-treated subjects. The severity of the DER was related to disulfiram dose and the trial with 500 mg/d was stopped prematurely due to safety concerns. The DER-related hypotension and tachycardia seen with ethanol infusion alone in disulfiram-treated subjects, was not exacerbated when combined with cocaine. In fact, cocaine tended to counteract the ethanol-related hypotension though it did exacerbate the tachycardia in two of seven subjects.

CONCLUSIONS

Though conclusions are limited by the moderate doses of cocaine, ethanol, and disulfiram tested, the data do suggest that the risks of the moderate use of cocaine and ethanol in individuals treated with moderate doses of disulfiram (≤ 250 mg/d) may not be as problematic as some may assume.

Can ropinirole modulate reinforcing subjective effects of cocaine in humans?

In this study we evaluated, by means of the "cocaine rush visual analog scale," the impact of ropinirole on the expected rush induced by cocaine in a group of heroin addicts abusing cocaine; the self-reported reaction to the rush blockade (if any) on cocaine consumption, and the correlations between this self-reported reaction and individual, clinical, and therapeutic parameters. Nineteen cocaine abuser heroin-dependent patients entered the study. Their experienced cocaine rush was 61.31 ± 32.1% of the maximum effect previously experienced. Compared with their previous rush intensity 16 patients experienced significantly lower intensity, 3 the same intensity, and none a higher intensity. In particular, two patients experienced a complete blockade of rush and reported a reduced use of cocaine. Fourteen patients experienced a partial blockade of cocaine rush; of these, nine reported they had reduced their use of cocaine. Ropinirole does diminish the subjective intensity of an expected cocaine rush, so interfering with the dynamics of reward, while supporting its possible use in the treatment of cocaine dependence.

Disulfiram, an option for the treatment of pathological gambling?

AIM

Pathological gambling and comorbid alcohol dependence often occur in combination. Disulfiram is one of the proven drugs for alcohol dependence. In addition to its inhibiting acetaldehyde dehydrogenase, disulfiram inhibits dopamine beta-hydroxylase and may thereby increase dopamine and decrease norepinephrine cerebral concentrations. Because there may be common neurochemical substrates and neuronal circuits for pathological gambling and addiction, we wished to explore the effect of disulfiram in gambling.

METHOD

We describe the outcome of a patient with alcohol dependence and pathological gambling treated with disulfiram D.

RESULTS

During treatment with disulfiram, the patient reported that his desire to gamble disappeared entirely. Follow-up indicated that he has not gambled for >12 months.

CONCLUSIONS

Although uncontrolled case observations should be interpreted with caution, disulfiram deserves further investigation in pathological gambling.

mechanisms of disulfiram-induced cocaine abstinence: antabuse and cocaine relapse

The anti-alcoholism drug disulfiram (Antabuse), which is an inhibitor of aldehyde dehydrogenase, induces an aversive reaction to alcohol consumption and thereby helps patients reduce alcohol intake. Recent clinical trials, initiated to investigate whether disulfiram could be used to treat individuals who abuse both alcohol and cocaine, have indicated that disulfiram effectively decreases cocaine consumption. Yet the ability of disulfiram to curb cocaine intake cannot be explained by the disruption of ethanol metabolism. Here, we synthesize clinical and animal data that point to dopamine beta-hydroxylase inhibition as a mechanism underlying the efficacy of disulfiram in the treatment of cocaine dependence.