Effects of phenytoin on cocaine self-administration in humans

Evaluation of the "Pipeline" for Development of Medications for Cocaine Use Disorder: A Review of Translational Preclinical, Human Laboratory, and Clinical Trial Research

Cocaine use disorder is a persistent public health problem for which no widely effective medications exist. Self-administration procedures, which have shown good predictive validity in estimating the abuse potential of drugs, have been used in rodent, nonhuman primate, and human laboratory studies to screen putative medications. This review assessed the effectiveness of the medications development process regarding pharmacotherapies for cocaine use disorder. The primary objective was to determine whether data from animal and human laboratory self-administration studies predicted the results of clinical trials. In addition, the concordance between laboratory studies in animals and humans was assessed. More than 100 blinded, randomized, fully placebo-controlled studies of putative medications for cocaine use disorder were identified. Of the 64 drugs tested in these trials, only 10 had been examined in both human and well-controlled animal laboratory studies. Within all three stages, few studies had been conducted for each drug and when multiple studies had been conducted conclusions were sometimes contradictory. Overall, however, there was good concordance between animal and human laboratory results when the former assessed chronic drug treatment. Although only seven of the ten reviewed drugs showed fully concordant results across all three types of studies reviewed, the analysis revealed several subject-related, procedural, and environmental factors that differ between the laboratory and clinical trial settings that help explain the disagreement for other drugs. The review closes with several recommendations to enhance translation and communication across stages of the medications development process that will ultimately speed the progress toward effective pharmacotherapeutic strategies for cocaine use disorder.

Phenytoin toxicity from cocaine adulteration

The use of phenytoin (PHT) as a cocaine adulterant was reported decades ago; that practice is still current. Ironically PHT has also been used for the treatment of cocaine dependence. A drug smuggler developed PHT toxicity after swallowing several rocks of crack. We investigated the current trends of PHT as a cocaine adulterant and its toxicological implications. We also reviewed the clinical use of PTH in relation to cocaine. The use of PHT as cocaine cut is a current practice. This may affect the clinical manifestations and the management of the cocaine-related visits to the emergency department.

Anticonvulsants for cocaine dependence

BACKGROUND

Cocaine dependence is a major public health problem that is characterised by recidivism and a host of medical and psychosocial complications. Although effective pharmacotherapy is available for alcohol and heroin dependence, none is currently available for cocaine dependence, despite two decades of clinical trials primarily involving antidepressant, anticonvulsivant and dopaminergic medications. Extensive consideration has been given to optimal pharmacological approaches to the treatment of individuals with cocaine dependence, and both dopamine antagonists and agonists have been considered. Anticonvulsants have been candidates for use in the treatment of addiction based on the hypothesis that seizure kindling-like mechanisms contribute to addiction.

OBJECTIVES

To evaluate the efficacy and safety of anticonvulsants for individuals with cocaine dependence.

SEARCH METHODS

We searched the Cochrane Drugs and Alcohol Group Trials Register (June 2014), the Cochrane Central Register of Controlled Trials (CENTRAL) (2014, Issue 6), MEDLINE (1966 to June 2014), EMBASE (1988 to June 2014), the Cumulative Index to Nursing and Allied Health Literature (CINAHL) (1982 to June 2014), Web of Science (1991 to June 2014) and the reference lists of eligible articles.

SELECTION CRITERIA

All randomised controlled trials and controlled clinical trials that focus on the use of anticonvulsant medications to treat individuals with cocaine dependence.

DATA COLLECTION AND ANALYSIS

We used the standard methodological procedures expected by The Cochrane Collaboration.

MAIN RESULTS

We included a total of 20 studies with 2068 participants. We studied the anticonvulsant drugs carbamazepine, gabapentin, lamotrigine, phenytoin, tiagabine, topiramate and vigabatrin. All studies compared anticonvulsants versus placebo. Only one study had one arm by which the anticonvulsant was compared with the antidepressant desipramine. Upon comparison of anticonvulsant versus placebo, we found no significant differences for any of the efficacy and safety measures. Dropouts: risk ratio (RR) 0.95, 95% confidence interval (CI) 0.86 to 1.05, 17 studies, 20 arms, 1695 participants, moderate quality of evidence. Use of cocaine: RR 0.92, 95% CI 0.84 to 1.02, nine studies, 11 arms, 867 participants, moderate quality of evidence; side effects: RR 1.39, 95% CI 1.01 to 1.90, eight studies, 775 participants; craving: standardised mean difference (SMD) -0.25, 95% CI -0.59 to 0.09, seven studies, eight arms, 428 participants, low quality of evidence.

AUTHORS' CONCLUSIONS

Although caution is needed when results from a limited number of small clinical trials are assessed, no current evidence supports the clinical use of anticonvulsant medications in the treatment of patients with cocaine dependence. Although the findings of new trials will improve the quality of study results, especially in relation to specific medications, anticonvulsants as a category cannot be considered first-, second- or third-line treatment for cocaine dependence.

Pharmacotherapeutics directed at deficiencies associated with cocaine dependence: focus on dopamine, norepinephrine and glutamate

Much effort has been devoted to research focused on pharmacotherapies for cocaine dependence yet there are no FDA-approved medications for this brain disease. Preclinical models have been essential to defining the central and peripheral effects produced by cocaine. Recent evidence suggests that cocaine exerts its reinforcing effects by acting on multiple neurotransmitter systems within mesocorticolimibic circuitry. Imaging studies in cocaine-dependent individuals have identified deficiencies in dopaminergic signaling primarily localized to corticolimbic areas. In addition to dysregulated striatal dopamine, norepinephrine and glutamate are also altered in cocaine dependence. In this review, we present these brain abnormalities as therapeutic targets for the treatment of cocaine dependence. We then survey promising medications that exert their therapeutic effects by presumably ameliorating these brain deficiencies. Correcting neurochemical deficits in cocaine-dependent individuals improves memory and impulse control, and reduces drug craving that may decrease cocaine use. We hypothesize that using medications aimed at reversing known neurochemical imbalances is likely to be more productive than current approaches. This view is also consistent with treatment paradigms used in neuropsychiatry and general medicine.

Modulation of ion channels in clinical psychopharmacology: adults and younger people

This review focuses on the use of Na(+), Ca(2+) and Cl(-) channel modulators in psychiatric disease. Drugs that modulate ion channels have been used in psychiatry for more than a century, and in this review we critically evaluate clinical research that reports the therapeutic effects of drugs acting on GABA(A), voltage-gated Na(+) and voltage-gated Ca(2+) channels in pediatric and adult patients. As in other fields, the evidence underpinning the use of medicines in younger people is far less robust than for adults. In addition, we discuss some current developments and highlight clinical disorders in which current molecules could be further tested. Notable success stories, such as benzodiazepines (in sleep and anxiety disorders) and antiepileptics (in bipolar disorder), have been the result of serendipitous discoveries or refinements of serendipitous discoveries, as in all other major treatments in psychiatry. Genomic, high-throughput screening and molecular pharmacology discoveries may, however, guide further developments in the future. This could include increased research in promising targets that have been perceived as commercially risky, such as selective α-subunit GABA(A) receptors.

Controversies in translational research: drug self-administration

RATIONALE

Laboratory animal and human models of drug self-administration are used to evaluate potential pharmacotherapies for drug abuse, yet the utility of these models in predicting clinically useful medications is variable.

OBJECTIVE

The objective of this study was to track how antagonist, agonist, and partial agonist medication approaches influence heroin and cocaine self-administration by rodents, non-human primates, and humans and to compare these results to clinical outcomes.

RESULTS

Across species, heroin self-administration was decreased by all three medication approaches, paralleling their demonstrated clinical utility. The heroin data emphasize the importance of assessing a medication's abuse liability preclinically to predict medication abuse and compliance and of considering subject characteristics (e.g., opioid dependence) when interpreting medication effects. For cocaine, the effects of ecopipam, modafinil, and aripiprazole were consistent in the laboratory and clinic, provided that the medications were administered repeatedly before self-administration sessions. Modafinil attenuated cocaine's reinforcing effects in the human laboratory and improved treatment outcome, while ecopipam and aripiprazole increased the reinforcing effects of cocaine and do not appear promising in the clinic.

CONCLUSIONS

The self-administration model has reliably identified medications to treat opioid dependence, and the recent data with modafinil suggest that the human laboratory model also identifies medications to treat cocaine dependence. There have been numerous false positives when subjective effects are the primary outcome measure, but not when self-administration is the outcome. Factors relevant to the predictive validity of self-administration procedures include medication maintenance and the concurrent assessment of a range of behaviors to determine abuse liability and the specificity of effect.

The role of human drug self-administration procedures in the development of medications

The purpose of this review is to illustrate the utility and value of employing human self-administration procedures in medication development, including abuse liability assessments of novel medications and evaluation of potential pharmacotherapies for substance use disorders. Traditionally, human abuse liability testing has relied primarily on subjective reports describing drug action by use of questionnaires; similarly, drug interactions between putative treatment agents and the drugs of abuse have relied on these measures. Subjective reports are highly valued because they provide qualitative and quantitative information about the characteristics of central and peripheral pharmacodynamic effects as well as safety and tolerability. However, self-administration procedures directly examine the behavior of interest-that is, drug taking. The present paper (1) reviews the most commonly used human self-administration procedures, (2) discusses the concordance of subjective reports and self-administration within the context of medications development for substance use disorders, focusing primarily on illustrative examples from development efforts with opioid and cocaine dependence, and (3) explores the utility of applying self-administration procedures to assess the abuse liability of novel compounds, including "abuse-deterrent" formulations (ADFs). The review will focus on opioid and cocaine dependence because a rich database from both clinical laboratory and clinical trial research exists for these two drug classes. The data reviewed suggest that drug-induced changes in self-administration and subjective effects are not always concordant. Therefore, assessment of self-administration in combination with subjective effects provides a more comprehensive picture that may have improved predictive validity for translating to the clinical setting.

Anticonvulsants for cocaine dependence

BACKGROUND

Cocaine dependence is a major public health problem that is characterized by recidivism and a host of medical and psychosocial complications. Although effective pharmacotherapy is available for alcohol and heroin dependence none exists currently for cocaine dependence despite two decades of clinical trials primarily involving antidepressant, anti convulsivant and dopaminergic medications. There has been extensive consideration of optimal pharmacological approaches to the treatment of cocaine dependence with consideration of both dopamine antagonists and agonists. Anticonvulsants have been candidates for the treatment of addiction based on the hypothesis that seizure kindling-like mechanisms contribute to addiction.

OBJECTIVES

To evaluate the efficacy and the acceptability of anticonvulsants for cocaine dependence

SEARCH STRATEGY

We searched the Cochrane Drugs and Alcohol Groups specialised register (issue 4, 2007), MEDLINE (1966 - march 2007), EMBASE (1988 - march 2007), CINAHL (1982- to march 2007)

SELECTION CRITERIA

All randomised controlled trials and controlled clinical trials which focus on the use of anticonvulsants medication for cocaine dependence

DATA COLLECTION AND ANALYSIS

Two authors independently evaluated the papers, extracted data, rated methodological quality

MAIN RESULTS

Fifteen studies (1066 participants) met the inclusion criteria for this review: the anticonvulsants drugs studied were carbamazepine, gabapentin, lamotrigine, phenytoin, tiagabine, topiramate, valproate. No significant differences were found for any of the efficacy measures comparing any anticonvulsants with placebo. Placebo was found to be superior to gabapentin in diminishing the number of dropouts, two studies, 81 participants, Relative Risk (RR) 3.56 (95% CI 1.07 to 11.82) and superior to phenythoin for side effects, two studies, 56 participants RR 2.12 (95% CI 1.08 to 4.17). All the other single comparisons are not statistically significant.

AUTHORS' CONCLUSIONS

Although caution is needed when assessing results from a limited number of small clinical trials at present there is no current evidence supporting the clinical use of anticonvulsants medications in the treatment of cocaine dependence. Aiming to answer the urgent demand of clinicians, patients, families, and the community as a whole for an adequate treatment for cocaine dependence, we need to improve the primary research in the field of addictions in order to make the best possible use out of a single study and to investigate the efficacy of other pharmacological agent.

A qualitative and quantitative review of cocaine-induced craving: the phenomenon of priming

Drug-induced craving is thought to play an important role in relapse occasioned by a "slip", or an isolated use of a previously abused drug after a period of abstinence. Clinical experience suggests that acute exposure to cocaine elicits craving (hereafter referred to as "priming"); however, this has received surprisingly little attention in the clinical literature.

AIMS

The intentions of this review are to provide a qualitative review of the literature as well as a more stringent quantitative review of the existence and presence of cocaine-induced priming effects.

METHODS

In order to determine whether priming effects occur following cocaine administration, we conducted qualitative and quantitative reviews of studies in which participants received cocaine under experimentally controlled conditions in the laboratory.

RESULTS

The results of the qualitative review were equivocal, while the quantitative review revealed that cocaine administration was associated with a significant increase in craving for cocaine, and the effect size of this relationship was large.

CONCLUSION

A review of the individual studies revealed marked variability, suggesting that priming effects did not occur consistently and that there may be factors that mediate or moderate the intensity of the priming effects induced by cocaine. The implications of these findings are discussed.

Effects of progesterone treatment on cocaine responses in male and female cocaine users

We recently reported that progesterone treatment attenuated some of the subjective effects of smoked cocaine in female cocaine users. In this study, we further examined the interaction between progesterone and cocaine in both male and female cocaine users using subjective, physiological and behavioral outcomes. A total of 10 subjects, 6 male and 4 female cocaine users, had two experimental sessions. Before each session, participants received either two oral doses of 200 mg of progesterone or placebo. Two hours after the second dose of medication treatment, the participants received a 0.3 mg/kg dose of cocaine intravenously and started the self-administration period, in which five optional doses of cocaine were available. Progesterone treatment attenuated the cocaine-induced diastolic blood pressure increases without affecting the systolic blood pressure and heart rate increases. Progesterone treatment also attenuated the subjective ratings of high and feel the effect of last dose in response to cocaine but did not affect cocaine self-administration behavior. These results suggest that progesterone attenuates some of the physiological and subjective effects of cocaine in both male and female participants. The effects of progesterone treatment on cocaine dependence need to be further studied in controlled trials.

Dextroamphetamine for cocaine-dependence treatment: a double-blind randomized clinical trial

A properly implemented agonist treatment regimen should improve retention and reduce illicit drug use. Cocaine-dependent subjects (N = 128) were enrolled in a 12-week randomized, double-blind, placebo-controlled trial. In the multistage dosing design, subjects initially received placebo (PBO) or 15 to 30 mg of dextroamphetamine sulfate, sustained-release capsules. At week 5, the dose doubled to 30 mg or 60 mg for active groups. Subjects attended the clinic twice a week, provided urine samples, obtained medication, and had one behavioral therapy session a week. Retention was best for the 15- to 30-mg group, whereas the proportion of benzoylecgonine-positive urine screens was, from lowest to highest, 30 to 60 mg, 15 to 30 mg, and PBO at study end. Dosing must be refined. The results provide support for additional examination of the agonist model in psychostimulant-dependence treatment.

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.

Predictors of cardiovascular response to smoked cocaine in humans

The purpose of this study was to examine the predictors of heart rate and blood pressure changes following cocaine administration. Sixty-two smoked cocaine users received a single 0.4 mg/kg dose of smoked cocaine. Male sex, African American race, higher body weight and current marijuana use predicted a greater cardiovascular response to cocaine. In contrast, higher baseline blood pressure, heart rate, amount and frequency of current cocaine use and presence of current cocaine snorting predicted a diminished cardiovascular response to cocaine. Whether these predictors of the cardiovascular response to smoked cocaine in the laboratory also predict cardiovascular complications from long-term cocaine use needs to be studied further.

Current concepts in pharmacotherapy of substance abuse

The cost to society of alcohol, tobacco, and illicit drug dependence is enormous. Although the importance of treatment for substance abuse to public health is increasingly acknowledged, pharmacotherapy is generally underutilized. However, the selection of medications for clinical testing is increasingly guided by the rapidly evolving science of addictive drugs and behavior. The benefit of medication for smoking cessation is firmly established, particularly for nicotine replacement and antidepressant therapy. Naltrexone is an important addition to the pharmacopoeia, and acamprosate may soon be approved as well. Although no new medications are approved for cocaine and amphetamine abuse, a variety of candidate treatments have shown promise in ongoing studies. Opiate substitution therapy is highly effective for rehabilitation of heroin addiction, and several alternative forms will soon be available; alternative forms of opiate detoxification have also received attention. Overall, there is increasing recognition that physicians have an obligation to identify and treat all forms of substance dependence, although knowledge of the efficacy of the available treatments is steadily increasing.