Comparison of the effects of methamphetamine, bupropion, and methylphenidate on the self-administration of methamphetamine by rhesus monkeys

Drug discrimination learning: Interoceptive stimulus control of behavior and its implications for regulated and dysregulated drug intake

Drug discrimination research has generated rich evidence for the capacity of interoceptive drug stimuli to control behavior by serving as discriminative cues. Owing to its neuropharmacological specificity, drug discrimination learning has been widely used to characterize the stimulus effects and neuropharmacological underpinning of drugs. Apart from such utility, discriminative drug stimuli may help regulate drug use by disambiguating conditioned associations and post-intake outcomes. First, this review summarizes the evidence supporting interoceptive regulation of drug intake from the literature of exteroceptive discriminative control of drug-related behavior, effects of drug priming, and self-titration of drug intake. Second, an overview of interoceptive control of reward-seeking and the animal model of discriminated goal-tracking is provided to illustrate interoceptive stimulus control of the initiation and patterning of drug intake. Third, we highlight the importance of interoceptive control of aversion-avoidance in the termination of drug-use episodes and describe the animal model of discriminated taste avoidance that supports such a position. In bridging these discriminative functions of drug stimuli, we propose that interoceptive drug stimuli help regulate intake by disambiguating whether intake will be rewarding, nonrewarding, or aversive. The reflection and discussion on current theoretical formulations of interoceptive control of drug intake may further scientific advances to improve animal models to study the mechanisms by which interoceptive stimuli regulate drug intake, as well as how alterations of interoceptive processes may contribute to the transition to dysregulated drug use.

Pharmacological Treatments for Methamphetamine Use Disorder: Current Status and Future Targets

The illicit use of the psychostimulant methamphetamine (METH) is a major concern, with overdose deaths increasing substantially since the mid-2010s. One challenge to treating METH use disorder (MUD), as with other psychostimulant use disorders, is that there are no available pharmacotherapies that can reduce cravings and help individuals achieve abstinence. The purpose of the current review is to discuss the molecular targets that have been tested in assays measuring the physiological, the cognitive, and the reinforcing effects of METH in both animals and humans. Several drugs show promise as potential pharmacotherapies for MUD when tested in animals, but fail to produce long-term changes in METH use in dependent individuals (eg, modafinil, antipsychotic medications, baclofen). However, these drugs, plus medications like atomoxetine and varenicline, may be better served as treatments to ameliorate the psychotomimetic effects of METH or to reverse METH-induced cognitive deficits. Preclinical studies show that vesicular monoamine transporter 2 inhibitors, metabotropic glutamate receptor ligands, and trace amine-associated receptor agonists are efficacious in attenuating the reinforcing effects of METH; however, clinical studies are needed to determine if these drugs effectively treat MUD. In addition to screening these compounds in individuals with MUD, potential future directions include increased emphasis on sex differences in preclinical studies and utilization of pharmacogenetic approaches to determine if genetic variances are predictive of treatment outcomes. These future directions can help lead to better interventions for treating MUD.

Efficacy of bupropion and cognitive behavioral therapy in the treatment of methamphetamine use disorder: a systematic review and meta-analysis

OBJECTIVES

We assessed the efficacy of cognitive behavioral therapy and bupropion compared to cognitive behavioral therapy alone for methamphetamine use disorder.

METHODS

The selection criteria for this systematic review study with meta-analysis were randomized clinical trials on the efficacy of cognitive behavioral therapy and bupropion in the treatment for methamphetamine use disorder (assessed by urine metabolites). The search was conducted in PubMed, PubMed Central, LILACS, SciELO, Cochrane Library, SCOPUS, Google Scholar, Ovid Medline, Clinicaltrials.gov, and the International Clinical Trials Registry Platform. The primary outcome was relapse. Risk of bias was assessed with the RoB 2 tool. The results of each clinical trial were input into an Excel spreadsheet. We performed a meta-analysis using relative risk and a 95%CI.

RESULTS

Of the 597 initial articles (498 after removing duplicate records), five were included in the meta-analysis, with an aggregate sample of 539 patients. An overall relative risk of 0.91 (95%CI 0.78-1.05) was estimated for relapse.

CONCLUSION

Our study limitations included publication bias and heterogeneous populations. We found no evidence that cognitive behavioral therapy and bupropion reduced the risk of relapse compared to cognitive behavioral therapy and placebo.

Effects of chronic treatment with bupropion on self-administration of nicotine + cocaine mixtures in nonhuman primates

Chronic health problems associated with long-term nicotine use are the leading cause of preventable death in the United States. The use of tobacco products is 3-4 times greater among individuals with cocaine use disorder than that observed in the general population. This may reflect the propensity of nicotine to augment the reinforcing effects of cocaine. However, the mechanism of action of nicotine differs from that of cocaine, which presents a significant challenge for the development of pharmacotherapeutic interventions for the management of nicotine + cocaine polydrug abuse. Bupropion, an FDA-approved smoking cessation aid, has pharmacological actions at both monoamine transporters and nicotinic receptors, suggesting that it may be effective at decreasing nicotine + cocaine coabuse. Here, rhesus monkeys (n = 4) responded for food pellets and, separately, intravenous injections of nicotine, cocaine, or nicotine + cocaine mixtures under a second-order FR2(VR16:S) schedule of reinforcement during 7- to 10-day continuous treatment with saline or bupropion (1.0 and 1.8 mg/kg/hr). Results show that bupropion treatment dose-dependently decreased self-administration of nicotine combined with a low dose of cocaine (0.0032 mg/kg/inj); however, when the dose of cocaine in the mixture was higher (i.e., 0.01 mg/kg/inj), bupropion attenuated self-administration in only a subset of subjects. The effective dosage of bupropion increased responding for cocaine alone, nicotine alone, and for saline injections and significantly increased measures of daily activity. The apparent stimulant-like effects of bupropion at the dosage required to decrease cocaine + nicotine self-administration does not support its clinical use for the management of nicotine + cocaine polydrug abuse. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Comparison of In Vitro Stereoselective Metabolism of Bupropion in Human, Monkey, Rat, and Mouse Liver Microsomes

BACKGROUND AND OBJECTIVES

Bupropion is an atypical antidepressant and smoking cessation aid associated with wide intersubject variability. This study compared the formation kinetics of three phase I metabolites (hydroxybupropion, threohydrobupropion, and erythrohydrobupropion) in human, marmoset, rat, and mouse liver microsomes. The objective was to establish suitability and limitations  for subsequent use of nonclinical species to model bupropion central nervous system (CNS) disposition in humans.

METHODS

Hepatic microsomal incubations were conducted separately for the R- and S-bupropion enantiomers, and the formation of enantiomer-specific metabolites was determined using LC-MS/MS. Intrinsic formation clearance (CL_int) of metabolites across the four species was determined from the formation rate versus substrate concentration relationship.

RESULTS

The total clearance of S-bupropion was higher than that of R-bupropion in monkey and human liver microsomes. The contribution of hydroxybupropion to the total racemic bupropion clearance was 38%, 62%, 17%, and 96% in human, monkey, rat, and mouse, respectively.  In the same species order, threohydrobupropion contributed 53%, 23%, 17%, and 3%, and erythrohydrobupropion contributed 9%, 14%, 66%, and 1.3%, respectively, to racemic bupropion clearance.

CONCLUSION

The results demonstrate that phase I metabolism in monkeys best approximates that observed in humans, and support the preferred use of this species to investigate possible pharmacokinetic factors that influence the CNS disposition of bupropion and contribute to its high intersubject variability.

Varenicline and GZ-793A differentially decrease methamphetamine self-administration under a multiple schedule of reinforcement in rats

Methamphetamine is a potent psychostimulant with high abuse rates. Currently, there is no Food and Drug Administration-approved pharmacotherapy for methamphetamine addiction. Ideally, a pharmacotherapy should selectively decrease methamphetamine self-administration without affecting responding for other reinforcers. One way to test this is with the use of a multiple schedule of reinforcement, in which drug and food are available in alternating components within a session. The present study evaluated GZ-793A, a vesicular monoamine transporter-2 inhibitor, and varenicline, a partial agonist at α4β2 and full agonist at α7 nicotinic acetylcholine receptors, for their ability to decrease methamphetamine and food self-administration using a multiple schedule of reinforcement. Male Sprague-Dawley rats self-administered methamphetamine (0.03 mg/kg/intravenous infusion) and food pellets under a multiple schedule of reinforcement. GZ-793A or varenicline was administered before multiple schedule sessions. GZ-793A (5 and 20 mg/kg) significantly decreased methamphetamine intake compared with saline and did not alter food-maintained responding. In contrast, varenicline decreased methamphetamine intake less specifically across time. The results suggest that vesicular monoamine transporter-2 inhibition may be a viable pharmacological target for the treatment of methamphetamine-use disorders.

Dopamine compartmentalization, selective dopaminergic vulnerabilities in Parkinson's disease and therapeutic opportunities

Progressive depletion of selected dopamine neurons is central to much Parkinson's disease (PD) disability. Although symptomatic treatments can ameliorate the disabilities that this neuronal depletion causes, no current strategy is documented to slow these losses. There is substantial evidence that dopamine in intracytoplasmic/extravesicular neuronal compartments can be toxic. Here, I review evidence that supports roles for dopamine compartmentalization, mediated largely by serial actions of plasma membrane SLC6A3/DAT and vesicular SLC18A2/VMAT2 transporters, in the selective patterns of dopamine neuronal loss found in PD brains. This compartmentalization hypothesis for the dopamine cell type specificity of PD lesions nominates available drugs for amelioration of damage arising from miscompartmentalized dopamine and raises cautions in using other drugs.

Utilizing a Two-stage Design to Investigate the Safety and Potential Efficacy of Monthly Naltrexone Plus Once-daily Bupropion as a Treatment for Methamphetamine Use Disorder

OBJECTIVES

This 2-stage open-label pilot study evaluated the safety and potential efficacy of naltrexone + bupropion as a pharmacotherapy for methamphetamine (MA) use disorder.

METHODS

The study was conducted in 2 stages of recruitment across 3 sites; 20 participants were enrolled in stage 1 and 29 participants were enrolled in stage 2. Eight weeks of open-label pharmacotherapy with a combination of extended-release injectable naltrexone (XR-NTX; Vivitrol) plus extended-release oral bupropion (BRP; Wellbutrin XL) were provided with a smartphone-assisted medication adherence platform. Participants met Diagnostic and Statistical Manual of Mental Disorders, 5th Edition criteria for severe MA use disorder, self-reported ≥20 days of MA use in the 30 days prior to consent, and submitted 3 MA-positive urine drug screens (UDS) out of 4 collected during screening. Participants attended clinic twice weekly for observed BRP dosing, UDS testing, assessments, and medical management; XR-NTX was administered at weeks 1 and 5. A BRP taper and follow-up visit occurred in week 9.

RESULTS

Analyses evaluated effects of XR-NTX + BRP to determine the number of "responders" according to a statistically predefined response criterion (6 of 8 MA-negative UDS during the last 4 weeks of medication). The 2-stage design required that stage 1 yield ≥3 responders to continue to stage 2; 11 of the 49 participants met responder criteria across both stages (5 in stage 1, 6 in stage 2).

CONCLUSIONS

Under the statistical analysis plan, study "success" required ≥9 responders. With 11 responders, the study demonstrated sufficient potential of naltrexone plus bupropion as a combination pharmacotherapy for MA use disorder to warrant further study.

Pharmacotherapeutic agents in the treatment of methamphetamine dependence

INTRODUCTION

Methamphetamine use is a serious public health concern in many countries and is second to cannabis as the most widely abused illicit drug in the world. Effective management for methamphetamine dependence remains elusive and the large majority of methamphetamine users relapse following treatment. Areas covered: Progression in the understanding of the pharmacological basis of methamphetamine use has provided us with innovative opportunities to develop agents to treat dependence. The current review summarizes relevant literature on the neurobiological and clinical correlates associated with methamphetamine use. We then outline agents that have been explored for potential treatments in preclinical studies, human laboratory phase I and phase II trials over the last ten years. Expert opinion: No agent has demonstrated a broad and strong effect in achieving MA abstinence in Phase II trials. Agents with novel therapeutic targets appear promising. Advancement in MA treatment, including translation into practice, faces several clinical challenges.

Utility of preclinical drug versus food choice procedures to evaluate candidate medications for methamphetamine use disorder

Substance use disorders are diagnosed as a manifestation of inappropriate behavioral allocation toward abused drugs and away from other behaviors maintained by more adaptive nondrug reinforcers (e.g., money and social relationships). Substance use disorder treatment goals include not only decreasing drug-maintained behavior but also promoting behavioral reallocation toward these socially adaptive alternative reinforcers. Preclinical drug self-administration procedures that offer concurrent access to both drug and nondrug reinforcers provide a translationally relevant dependent measure of behavioral allocation that may be useful for candidate medication evaluation. In contrast to other abused drugs, such as heroin or cocaine, preclinical methamphetamine versus food choice procedures have been a more recent development. We hypothesize that preclinical to clinical translatability would be improved by the evaluation of repeated pharmacological treatment effects on methamphetamine self-administration under a methamphetamine versus food choice procedure. In support of this hypothesis, a literature review suggests strong concordance between preclinical pharmacological treatment effects on methamphetamine versus food choice in nonhuman primates and clinical medication treatment effects on methamphetamine self-administration in human laboratory studies or methamphetamine abuse metrics in clinical trials. In conclusion, this literature suggests preclinical methamphetamine versus food choice procedures may be useful in developing innovative pharmacotherapies for methamphetamine use disorder.

Delayed emergence of methamphetamine's enhanced cardiovascular effects in nonhuman primates during protracted methamphetamine abstinence

BACKGROUND

Methamphetamine abuse is linked with brain abnormalities, but its peripheral effects constitute an integral aspect of long-term methamphetamine use.

METHODS

Eight male rhesus monkeys with long histories of intravenous methamphetamine self-administration were evaluated 1 day, and 1, 4, 12, 26, and 52 weeks after their last methamphetamine self-administration session. On test days, isoflurane-anesthetized animals received a 0.35 mg/kg IV methamphetamine challenge. A control group consisted of 10 age and gender matched drug naïve monkeys. Cardiovascular responses to methamphetamine were followed for 2.5h. Echocardiograms were acquired at 3 and 12 months of abstinence and in the control animals.

RESULTS

No pre-methamphetamine baseline differences existed among 7 physiological measures across all conditions and controls. As expected, methamphetamine increased heart rate and blood pressure in controls. However, immediately following the self-administration period, the blood pressure response to methamphetamine challenge was reduced when compared to control monkeys. The peak and 150-min average heart rate increases, as well as peak blood pressure increases following methamphetamine were significantly elevated between weeks 12 to 26 of abstinence. These data indicate the development of tolerance followed by sensitization to methamphetamine cardiovascular effects. Echocardiography demonstrated decreased left ventricular ejection fraction and cardiac output at 3 months of abstinence. Importantly, both cardiovascular sensitization and cardiotoxicity appeared to be reversible as they returned toward control group levels after 1 year of abstinence.

CONCLUSIONS

Enhanced cardiovascular effects may occur after prolonged abstinence in addicts relapsing to methamphetamine and may underlie clinically reported acute cardiotoxic events.

Differential effects of bupropion on acquisition and performance of an active avoidance task in male mice

Bupropion is an antidepressant drug that is known to aid smoking cessation, although little experimental evidence exists about its actions on active avoidance learning tasks. Our aim was to evaluate the effects of this drug on two-way active avoidance conditioning. In this study, NMRI mice received bupropion (10, 20 and 40mg/kg) or saline before a daily training session (learning phase, days 1-4) in the active avoidance task. Performance was evaluated on the fifth day (retention phase): in each bupropion-treated group half of the mice continued with the same dose of bupropion, and the other half received saline. Among the vehicle-treated mice, different sub-groups were challenged with different doses of bupropion. Results indicated that mice treated with 10 and 20mg/kg bupropion exhibited more number of avoidances during acquisition. The response latency confirmed this learning improvement, since this parameter decreased after bupropion administration. No differences between groups were observed in the retention phase. In conclusion, our data show that bupropion influences the learning process during active avoidance conditioning, suggesting that this drug can improve the control of emotional responses.

Exposure to methylphenidate during infancy and adolescence in non-human animals and sensitization to abuse of psychostimulants later in life: a systematic review

INTRODUCTION

Attention deficit hyperactivity disorder (ADHD) is a neuropsychiatric pathology that has an important prevalence among young people and is difficult to diagnose. It is usually treated with methylphenidate, a psychostimulant with a mechanism of action similar to that of cocaine. Previous studies show that repeated use of psychostimulants during childhood or adolescence may sensitize subjects, making them more prone to later abuse of psychostimulant drugs such as cocaine and methamphetamine.

OBJECTIVE

To review experimental studies in non-human models (rodents and monkeys) treated with methylphenidate during infancy or adolescence and tested for reinforcing effects on psychostimulant drugs in adulthood.

METHOD

Systematic collection of data was performed on four databases (Web of Knowledge, PsycARTICLE, PubMed and SciELO). The initial search identified 202 articles published from 2009 to 2014, which were screened for eligibility. Seven articles met the inclusion criteria and were reviewed in this study.

RESULTS

The findings indicate that early exposure to methylphenidate has an effect on an ADHD animal model, specifically, on spontaneously hypertensive strain rats, especially those tested using the self-administration paradigm.

CONCLUSION

Future studies should prioritize the spontaneously hypertensive rat strain - an animal model of ADHD. Experimental designs comparing different behavioral paradigms and modes of administration using this strain could lead to improved understanding of the effects of exposure to methylphenidate during childhood and adolescence.

Effects of 7-day continuous D-amphetamine, methylphenidate, and cocaine treatment on choice between methamphetamine and food in male rhesus monkeys

BACKGROUND

Methamphetamine addiction is a significant public health problem for which no Food and Drug Administration-approved pharmacotherapies exist. Preclinical drug vs. food choice procedures have been predictive of clinical medication efficacy in the treatment of opioid and cocaine addiction. Whether preclinical choice procedures are predictive of candidate medication effects for other abused drugs, such as methamphetamine, remains unclear. The present study aim was to determine continuous 7-day treatment effects with the monoamine releaser d-amphetamine and the monoamine uptake inhibitor methylphenidate on methamphetamine vs. food choice. In addition, 7-day cocaine treatment effects were also examined.

METHODS

Behavior was maintained under a concurrent schedule of food delivery (1-g pellets, fixed-ratio 100 schedule) and methamphetamine injections (0-0.32mg/kg/injection, fixed-ratio 10 schedule) in male rhesus monkeys (n=4). Methamphetamine choice dose-effect functions were determined daily before and during 7-day periods of continuous intravenous treatment with d-amphetamine (0.01-0.1mg/kg/h), methylphenidate (0.032-0.32mg/kg/h), or cocaine (0.1-0.32mg/kg/h).

RESULTS

During saline treatment, increasing methamphetamine doses resulted in a corresponding increase in methamphetamine vs. food choice. Continuous 7-day treatments with d-amphetamine, methylphenidate or cocaine did not significantly attenuate methamphetamine vs. food choice up to doses that decreased rates of operant responding. However, 0.1mg/kg/h d-amphetamine did eliminate methamphetamine choice in two monkeys.

CONCLUSIONS

The present subchronic treatment results support the utility of preclinical methamphetamine choice to evaluate candidate medications for methamphetamine addiction. Furthermore, these results confirm and extend previous results demonstrating differential pharmacological mechanisms between cocaine choice and methamphetamine choice.

Effects of Environmental Manipulations and Treatment with Bupropion and Risperidone on Choice between Methamphetamine and Food in Rhesus Monkeys

Preclinical and human laboratory choice procedures have been invaluable in improving our knowledge of the neurobiological mechanisms of drug reinforcement and in the drug development process for candidate medications to treat drug addiction. However, little is known about the neuropharmacological mechanisms of methamphetamine vs food choice. The aims of this study were to develop a methamphetamine vs food choice procedure and determine treatment effects with two clinically relevant compounds: the monoamine uptake inhibitor bupropion and the dopamine antagonist risperidone. Rhesus monkeys (n=6) responded under a concurrent schedule of food delivery (1-g pellets, fixed-ratio (FR) 100 schedule) and intravenous methamphetamine injections (0-0.32 mg/kg/injection, FR10 schedule) during 7-day bupropion (0.32-1.8 mg/kg/h) and risperidone (0.001-0.0056 mg/kg/h) treatment periods. For comparison, effects of removing food pellets or methamphetamine injections and FR response requirement manipulations were also examined. Under saline treatment conditions, food was preferred over no methamphetamine or small unit methamphetamine doses (0.01-0.032 mg/kg/injection). Larger methamphetamine doses resulted in greater methamphetamine preference and 0.32 mg/kg/injection methamphetamine maintained near exclusive preference. Removing food availability increased methamphetamine choice, whereas removing methamphetamine availability decreased methamphetamine choice. Methamphetamine choice was not significantly altered when the FR response requirements for food and drug were the same (FR100:FR100 or FR10:FR10). Risperidone treatment increased methamphetamine choice, whereas bupropion treatment did not alter methamphetamine choice up to doses that decreased rates of operant behavior. Overall, these negative results with bupropion and risperidone are concordant with previous human laboratory and clinical trials and support the potential validity of this preclinical methamphetamine vs food choice model.

Withdrawal from long-term methamphetamine self-administration 'normalizes' neurometabolites in rhesus monkeys: a (1) H MR spectroscopy study

(1) H magnetic resonance spectroscopy has demonstrated alterations in several neurometabolites in methamphetamine (METH)-dependent individuals in brain regions implicated in addiction. Yet, it is unclear whether these neurochemicals return to homeostatic levels after an individual abstains from drug use, a difficult question to address due to high recidivism and poor study retention in human subjects. We thus utilized a non-human primate model of addiction to explore the effects of long-term drug exposure and withdrawal on brain neurochemistry. Ten rhesus macaque monkeys on an active METH self-administration protocol (average use 4.6 ± 0.8 years, average daily intake between 0.4 and 1.2 mg/kg) and 10 age- and sex-matched drug-naive controls (CONT) served as subjects. Concentrations of several neurochemicals were evaluated at several timepoints following withdrawal from drug availability (10 monkeys at 1 week and 1 and 3 months, and 6 monkeys at 6 and 12 months; CONT examined at one timepoint). At 1 week following METH withdrawal, we found increases in myo-inositol in anterior cingulate cortex in the METH group relative to CONT. These alterations showed a linear pattern of decreased levels ('normalization') by 1 year of abstinence. We also found decreases in glutamine and Glx (composed mainly of glutamate and glutamine) in the caudate-putamen of the same animals at early withdrawal that showed a similar linear pattern of increasing concentration by 1 year. These results demonstrate that despite protracted, long-term use, neurochemical changes seen following long-term drug administration do not persist following prolonged abstinence, suggesting therapeutic effects of long-term withdrawal from drug use.

Naltrexone and bupropion, alone or combined, do not alter the reinforcing effects of intranasal methamphetamine

Naltrexone and bupropion, when administered alone in clinical trials, modestly reduce amphetamine use. Whether combining these drugs would result in greater reductions in methamphetamine taking relative to either drug alone is undetermined. This study examined the influence of naltrexone, bupropion and a naltrexone-bupropion combination on methamphetamine self-administration in humans. Seven subjects reporting recent illicit stimulant use completed a placebo-controlled, crossover, double-blind study in which the reinforcing, subject-rated and physiological effects of intranasal methamphetamine (0, 10 and 30 mg) were assessed during maintenance on placebo, naltrexone (50 mg), bupropion (300 mg/day), and naltrexone combined with bupropion. Methamphetamine maintained responding and produced prototypic subjective and physiological effects (e.g., increased ratings of good effects, elevated systolic blood pressure). Maintenance doses were well tolerated and generally devoid of effects. No maintenance condition reduced methamphetamine self-administration or systematically altered the subject-rated effects of methamphetamine. These outcomes demonstrate the robust behavioral effects of methamphetamine that could make it resistant to pharmacological manipulation. Although these outcomes indicate that this combination may be ineffective for managing methamphetamine use disorder, future work should evaluate longer maintenance dosing, individuals with different levels of amphetamine use, adding this combination to a behavioral platform and other pharmacotherapy combinations for reducing methamphetamine use.

Randomized, placebo-controlled trial of bupropion in methamphetamine-dependent participants with less than daily methamphetamine use

AIMS

Two previous randomized trials found an effect for bupropion in reducing methamphetamine use in the subgroup with lower frequency of methamphetamine use at baseline. This study aimed to replicate these results by comparing bupropion versus placebo in methamphetamine-dependent participants with less than daily methamphetamine use at baseline.

METHODS

Methamphetamine-dependent volunteers reporting methamphetamine use on ≤29 of past 30 days were randomized to bupropion 150 mg twice daily (n = 41) or placebo (n = 43) and out-patient counseling for 12 weeks. The primary outcome was the proportion achieving end-of-treatment (EOT) methamphetamine abstinence (weeks 11 and 12) for bupropion versus placebo. A post-hoc analysis compared EOT abstinence by medication adherence assessed via plasma bupropion/hydroxybupropion level.

RESULTS

There was no significant difference in EOT abstinence between bupropion (29%, 12 of 41) and placebo (14%, six of 43; P = 0.087). Among participants receiving bupropion, EOT abstinence was significantly higher in participants assessed as medication adherent by plasma bupropion/hydroxybupropion levels (54%, seven of 13) compared to non-adherent participants (18%, five of 28; P = 0.018). Medication adherence by plasma levels was low (32%).

CONCLUSIONS

Bupropion may be efficacious for reducing methamphetamine in people with less than daily baseline methamphetamine use, but the evidence remains inconclusive.

Pharmacotherapy for stimulant-related disorders

Stimulant-related disorders (SRD) continue to be an important public health problem for which there are presently no approved pharmacotherapies. Although behavioral interventions provide some benefit response varies. The development of novel and effective pharmacotherapies continues to be a research priority. Understanding neural mechanisms critical to the action of stimulants has helped reveal several potential pharmacotherapies that have already shown promise in controlled clinical trials. Common to some of these medications is the ability to reverse neural deficits in individuals with SRD. Results from thoroughly conducted clinical trials continue to broaden our knowledge increasing the possibility of soon developing effective pharmacotherapies for SRD.

A preclinical evaluation of the discriminative and reinforcing properties of lisdexamfetamine in comparison to D-amfetamine, methylphenidate and modafinil

Lisdexamfetamine dimesylate, which consists of L-lysine covalently bound to D-amfetamine, is the first prodrug for treating ADHD. Its metabolic conversion to yield D-amfetamine by rate-limited, enzymatic hydrolysis is unusual because it is performed by peptidases associated with red blood cells. Other stimulants shown to be effective in managing ADHD include D-amfetamine, methylphenidate and modafinil. All have the potential for misuse or recreational abuse. The discriminative and reinforcing effects of these compounds were determined in rats using a 2-choice, D-amfetamine (0.5 mg/kg, i.p.)-cued drug-discrimination test, and by substitution for intravenous cocaine in self-administration. Lisdexamfetamine (0.5-1.5 mg/kg [D-amfetamine base], p.o.) generalised to saline when tested 15 min post-dosing, but dose-dependently generalised to d-amfetamine at 60 min. At 120 min, its D-amfetamine-like effects were substantially diminished. At 15 min, methylphenidate (3.0-10 mg/kg, p.o.) and D-amfetamine (0.1-1.5 mg/kg, p.o.) dose-dependently generalised to the intraperitoneal D-amfetamine cue. Switching to the intraperitoneal route reduced the interval required for lisdexamfetamine to be recognised as D-amfetamine-like, but did not alter its potency. Switching to intraperitoneal injection increased the potency of methylphenidate and D-amfetamine by 3.4× and 2.2×, respectively. Modafinil (50-200 mg/kg, i.p.) generalised partially, but not fully, to d-amfetamine. Methylphenidate (0.1, 0.3, 1.0 mg/kg/injection, i.v.) maintained robust self-administration at the 2 highest doses. Neither lisdexamfetamine (0.05, 0.15 or 0.5 mg/kg/injection [D-amfetamine base], i.v.) nor modafinil (0.166, 0.498 or 1.66 mg/kg/injection, i.v.) served as reinforcers. The results reveal important differences between the profiles of these stimulants. Lisdexamfetamine did not serve as a positive reinforcer in cocaine-trained rats, and although it generalised fully to D-amfetamine, its discriminative effects were markedly influenced by its unusual pharmacokinetics.

Bupropion, methylphenidate, and 3,4-methylenedioxypyrovalerone antagonize methamphetamine-induced efflux of dopamine according to their potencies as dopamine uptake inhibitors: implications for the treatment of methamphetamine dependence

BACKGROUND

Methamphetamine-abuse is a worldwide health problem for which no effective therapy is available. Inhibition of methamphetamine-induced transporter-mediated dopamine (DA) release could be a useful approach to treat methamphetamine-addiction. We assessed the potencies of bupropion, methylphenidate, and 3,4-methylenedioxypyrovalerone (MDPV) to block DA uptake or to inhibit methamphetamine-induced DA release in HEK-293 cells expressing the human DA transporter.

FINDINGS

Bupropion, methylphenidate, and MDPV inhibited methamphetamine-induced DA release with relative potencies corresponding to their potencies to block DA uptake (potency ranks: MDPV > methylphenidate > bupropion).

CONCLUSIONS

Bupropion and methylphenidate antagonize the effects of methamphetamine in vitro and may be potential candidates for the treatment of stimulant addiction. However, drugs that very potently antagonize the effect of methamphetamine are likely to also exhibit considerable abuse liability (MDPV > methylphenidate > bupropion).

Bupropion induced changes in exploratory and anxiety-like behaviour in NMRI male mice depends on the age

The aim of this study was to assess the effects of the antidepressant bupropion on anxiety and novelty-seeking in adolescent mice of different ages and adults. Behavioural differences between early adolescent, late adolescent and adult NMRI mice were measured both in the elevated plus-maze and the hole-board tasks following acute administration of bupropion (5, 10, 15, 20mg/kg) or saline. In the plus maze test, early and late adolescent mice treated with bupropion (10, 15mg/kg, respectively) had lower percentages of entries in the open-arms compared to their vehicle controls. Adult mice treated with bupropion did not differ from their vehicle controls. These results suggest that the effect of this drug on anxiety-like behaviour in mice depends on the age, showing adolescents an anxiogenic-like profile. In the hole-board, adolescents showed more elevated levels of novelty-seeking than adults, exhibiting shorter latency to the first head-dip (HD) and a higher number of HD's. Bupropion increases the latency to the first HD and decreases the number of HD's in all age-groups, indicating a decline in exploratory tendency. Findings reveal that the age can modulate the behaviour displayed by mice in both animal models, and that adolescents are more sensitive to bupropion's anxiogenic effects.

A novel, nonbinary evaluation of success and failure reveals bupropion efficacy versus methamphetamine dependence: reanalysis of a multisite trial

A multisite, double-blind, placebo-controlled trial of bupropion for methamphetamine dependence was reanalyzed using a novel, nonbinary method of evaluating success and failure. The original analysis focused on a group response endpoint (the change in percentage of participants with methamphetamine-free urines each week over the course of the trial) and no significant bupropion effect was observed in the total population of study participants. In this reanalysis, individual participants were regarded as treatment success if they achieved multiple weeks of abstinence lasting through the end of the study, and their degree of success was quantified by calculating the number of beyond-threshold weeks of success (NOBWOS). Thus, setting the threshold at 1 week of end-of-study abstinence (EOSA), treatment successes were assigned NOBWOS values ranging from 1 to 11, with 1 corresponding to 2 weeks EOSA and 11 corresponding to abstinence throughput the entire 12-week trial. Treatment failures were assigned a value of 0. Comparison of NOBWOS values revealed a significant effect of bupropion to facilitate abstinence (P= 0.0176). In the bupropion group, 20% of participants achieved 2 or more weeks EOSA, 14% achieved 6 or more weeks EOSA, and 6% were abstinent throughout the trial; this compares with 7%, 4%, and 1% in the placebo group, respectively. On the basis of the NOBWOS analysis, bupropion seems to effectively facilitate the achievement of abstinence in methamphetamine-dependent individuals.