Safety of intravenous methamphetamine administration during treatment with bupropion

Methamphetamine increases force of contraction in isolated human atrial preparations through the release of noradrenaline

We measured the cardiac contractile effects of the sympathomimetic amphetamine-like drug methamphetamine alone and in the presence of cocaine or propranolol in human atrial preparations. For a more comprehensive analysis, we also examined the effects of methamphetamine in preparations from the left and right atria of mice and, for comparison, analyzed the cardiac effects of amphetamine itself. In human atrial preparations, methamphetamine and amphetamine increased the contractile force, the relaxation rate, and the rate of tension development, and shortened the time to maximum tension and the time to relaxation. Likewise, in mice preparations, methamphetamine and amphetamine increased the contractile force in the left atrium and increased the beating rate in the right atrium. The effect in human atrial preparations started at 1µM, therefore methamphetamine was less effective and potent than isoproterenol in increasing contractile force. These positive inotropic effects of methamphetamine were greatly attenuated by 10µM cocaine and abolished by 10µM propranolol. The inotropic effects of methamphetamine in human atrial preparations were associated with, and are believed to be mediated at least in part by, an increase in the phosphorylation state of the inhibitory subunit of troponin. In conclusion, the sympathomimetic central stimulant drug methamphetamine (as well as amphetamine) increased contractile force and protein phosphorylation, presumably through a release of noradrenaline in isolated human atrial preparations. Thus, methamphetamine acts as an indirect sympathomimetic in the human atrium.

Immunopharmacotherapeutic advancements in addressing methamphetamine abuse

Methamphetamine (METH) is an illicit psychostimulant that is known to account for substance abuse disorders globally, second only to opioids, yet has no approved pharmacotherapies. Traditional therapies employ small molecule agonists or antagonists for substance use disorders or overdose reversal by targeting drug-specific receptors in the brain. However, the comprehensive mechanism of METH on multiple sites within the central nervous system (CNS) implies its receptors lack the high affinity and specificity required for an "ideal" drug target. The alternative to pharmacotherapies is to sequester abused drugs in the periphery, effectively eliminating the effects from CNS receptor occupation through pharmacokinetic antagonism. This review presents updates on immunopharmacotherapeutic advancements in addressing methamphetamine abuse by focusing on the cultivation of research optimization strategies regarding hapten chemistry, carrier proteins, and adjuvants implemented in active immunization. Furthermore, we discuss necessary developments for each component of active immunopharmacotherapies and the future of active vaccines in treating METH use disorder.

Drug-Induced Craving for Methamphetamine Is Associated With Neural Methamphetamine Cue Reactivity

OBJECTIVE

Drug craving serves as the major motivator to propagate drug use and is thought to elicit relapse in abstinent individuals. Although craving for methamphetamine has been investigated using both laboratory and neuroimaging methodologies, the relationship between drug-induced craving and neural responses to methamphetamine cues has yet to be explored. Therefore, the present study investigated whether methamphetamine-induced craving responses in the laboratory were associated with neural response to methamphetamine cues.

METHOD

Non-treatment-seeking individuals with methamphetamine use disorder (n = 15) completed two sessions, one in the laboratory where they underwent a methamphetamine infusion, and one in the magnetic resonance imaging scanner where they viewed methamphetamine cues. Participants reported their craving for methamphetamine over the course of the laboratory session. Analyses examined the association between peak ratings of methamphetamine-induced craving and neural activation to methamphetamine cues.

RESULTS

In individuals with a methamphetamine use disorder, methamphetamine-induced craving was positively associated with neural methamphetamine cue reactivity in the precuneus, putamen, and ventromedial prefrontal cortex (Z > 2.3, p < .05).

CONCLUSIONS

There is a shared neurobiology underlying cue- and drug-induced craving in individuals with methamphetamine use disorder. Treatments that disrupt this circuitry may decrease craving and help prevent relapse.

Mechanistic PBPK Modeling of Urine pH Effect on Renal and Systemic Disposition of Methamphetamine and Amphetamine

The effect of urine pH on renal excretion and systemic disposition has been observed for many drugs and metabolites. When urine pH is altered, tubular ionization, passive reabsorption, renal clearance, and systemic exposure of drugs and metabolites may all change dramatically, raising clinically significant concerns. Surprisingly, the urine pH effect on drug disposition is not routinely explored in humans, and regulatory agencies have neither developed guidance on this issue nor required industry to conduct pertinent human trials. In this study, we hypothesized that physiologically based pharmacokinetic (PBPK) modeling could be used as a cost-effective method to examine potential urine pH effect on drug and metabolite disposition. Our previously developed and verified mechanistic kidney model was integrated with a full-body PBPK model to simulate renal clearance and area under the plasma concentration-time curve (AUC) with varying urine pH statuses using methamphetamine and amphetamine as model compounds. We first developed and verified drug models for methamphetamine and amphetamine under normal urine pH condition [absolute average fold error (AAFE) < 1.25 at study level]. Then, acidic and alkaline urine scenarios were simulated. Our simulation results show that the renal excretion and plasma concentration-time profiles for methamphetamine and amphetamine could be recapitulated under different urine pH (AAFE < 2 at individual level). The methamphetamine-amphetamine parent-metabolite full-body PBPK model also successfully simulated amphetamine plasma concentration-time profiles (AAFE < 1.25 at study level) and amphetamine/methamphetamine urinary concentration ratios (AAFE < 2 at individual level) after dosing methamphetamine. This demonstrates that our mechanistic PBPK model can predict urine pH effect on systemic and urinary disposition of drugs and metabolites. SIGNIFICANCE STATEMENT: Our study shows that integrating mechanistic kidney model with full-body physiologically based pharmacokinetic model can predict the magnitude of alteration in renal excretion and area under the plasma concentration-time curve (AUC) of drugs and metabolites when urine pH is changed. This provides a cost-effective method to evaluate the likelihood of renal and systemic disposition changes due to varying urine pH. This is important because multiple drugs and diseases can alter urine pH, leading to quantitatively and clinically significant changes in drug and metabolite disposition that may require adjustment of therapy.

A virtual reality counterconditioning procedure to reduce methamphetamine cue-induced craving

The present work developed a virtual reality (VR) counterconditioning procedure (VRCP), and investigated its efficacy in treatment of cue-induced craving in individuals with methamphetamine (METH) dependence. In study 1, thirty-one patients diagnosed with METH dependence received VRCP, while twenty-nine METH-dependent patients in waiting-list group did not. In study 2, the VRCP was computerized as a VR treatment system. Six-hundred and twelve abstinent individuals with a history of METH dependence received the computerized VRCP, while two-hundred seventy-six abstinent individuals with a history of METH dependence in waiting-list group did not. Patients with METH dependence who received VRCP showed a significantly larger decrease on the score of METH-craving and METH-liking from baseline to follow-up assessments, compared to those who did not received VRCP. Participants received VRCP showed a significantly larger decrease in HRV indexes on time domain and non-linear domain from baseline to follow-up assessments during exposure to VR cues, compared to those in waiting-list group. These findings indicate that the counterconditioning procedure under VR environment may be a useful strategy in suppressing cue-induced reactivity for patients with METH dependence.

The effect of N-acetylcysteine or bupropion on methamphetamine self-administration and methamphetamine-triggered reinstatement of female rats

N-acetylcysteine and bupropion are two promising candidate medications for treatment of substance use disorder. The effects of N-acetylcysteine or bupropion on methamphetamine self-administration of female rats are not well understood. To fill this gap, this study assessed the effects of N-acetylcysteine (0, 30, 60, or 120 mg/kg) and bupropion (0, 10, 30, and 60 mg/kg) on methamphetamine self-administration of female rats across the natural estrous cycle. Following a completed dose-response curve, responding for methamphetamine self-administration was extinguished and the effects of N-acetylcysteine or bupropion on methamphetamine-triggered reinstatement was evaluated in separate experiments. N-acetylcysteine did not decrease responding maintained by methamphetamine or methamphetamine-triggered reinstatement. Bupropion significantly decreased methamphetamine self-administration and methamphetamine-triggered reinstatement in female rats with highest dose (60 mg/kg) also significantly decreasing general chamber activity. In a companion experiment, testing the effect of bupropion on responding maintained by sucrose, we confirmed non-specificity of bupropion's effects as bupropion also decreased responding for sucrose. Considered together, our findings suggest that while N-acetylcysteine has considerable promise for treatment of cocaine dependence it may not generalize to other stimulants like methamphetamine. Furthermore, although bupropion has been shown to effectively decrease methamphetamine self-administration, and presently methamphetamine-triggered reinstatement, its locomotor and reward suppressing effects warrant further investigation including both sexes.

Interaction and Transport of Methamphetamine and its Primary Metabolites by Organic Cation and Multidrug and Toxin Extrusion Transporters

Methamphetamine is one of the most abused illicit drugs with roughly 1.2 million users in the United States alone. A large portion of methamphetamine and its metabolites is eliminated by the kidney with renal clearance larger than glomerular filtration clearance. Yet the mechanism of active renal secretion is poorly understood. The goals of this study were to characterize the interaction of methamphetamine and its major metabolites with organic cation transporters (OCTs) and multidrug and toxin extrusion (MATE) transporters and to identify the major transporters involved in the disposition of methamphetamine and its major metabolites, amphetamine and para-hydroxymethamphetamine (p-OHMA). We used cell lines stably expressing relevant transporters to show that methamphetamine and its metabolites inhibit human OCTs 1-3 (hOCT1-3) and hMATE1/2-K with the greatest potencies against hOCT1 and hOCT2. Methamphetamine and amphetamine are substrates of hOCT2, hMATE1, and hMATE2-K, but not hOCT1 and hOCT3. p-OHMA is transported by hOCT1-3 and hMATE1, but not hMATE2-K. In contrast, organic anion transporters 1 and 3 do not interact with or transport these compounds. Methamphetamine and its metabolites exhibited complex interactions with hOCT1 and hOCT2, suggesting the existence of multiple binding sites. Our studies suggest the involvement of the renal OCT2/MATE pathway in tubular secretion of methamphetamine and its major metabolites and the potential of drug-drug interactions with substrates or inhibitors of the OCTs. This information may be considered when prescribing medications to suspected or known abusers of methamphetamine to mitigate the risk of increased toxicity or reduced therapeutic efficacy.

In vitro to in vivo extrapolation of the complex drug-drug interaction of bupropion and its metabolites with CYP2D6; simultaneous reversible inhibition and CYP2D6 downregulation

Bupropion is a widely used antidepressant and smoking cessation aid and a strong inhibitor of CYP2D6 in vivo. Bupropion is administered as a racemic mixture of R- and S-bupropion and has stereoselective pharmacokinetics. Four primary metabolites of bupropion, threo- and erythro-hydrobupropion and R,R- and S,S-OH-bupropion, circulate at higher concentrations than the parent drug and are believed to contribute to the efficacy and side effects of bupropion as well as to the CYP2D6 inhibition. However, bupropion and its metabolites are only weak inhibitors of CYP2D6 in vitro, and the magnitude of the in vivo drug-drug interactions (DDI) caused by bupropion cannot be explained by the in vitro data even when CYP2D6 inhibition by the metabolites is accounted for. The aim of this study was to quantitatively explain the in vivo CYP2D6 DDI magnitude by in vitro DDI data. Bupropion and its metabolites were found to inhibit CYP2D6 stereoselectively with up to 10-fold difference in inhibition potency between enantiomers. However, the reversible inhibition or active uptake into hepatocytes did not explain the in vivo DDIs. In HepG2 cells and in plated human hepatocytes bupropion and its metabolites were found to significantly downregulate CYP2D6 mRNA in a concentration dependent manner. The in vivo DDI was quantitatively predicted by significant down-regulation of CYP2D6 mRNA and reversible inhibition of CYP2D6 by bupropion and its metabolites. This study is the first example of a clinical DDI resulting from CYP down-regulation and first demonstration of a CYP2D6 interaction resulting from transcriptional regulation.

Safety of Intravenous Methamphetamine Administration During Ibudilast Treatment

BACKGROUND

Methamphetamine dependence is a significant public health concern without any approved medications for treatment. We evaluated ibudilast, a nonselective phosphodiesterase inhibitor, to assess the safety and tolerability during intravenous methamphetamine administration. We conducted a randomized, double-blind, placebo-controlled, within-subjects crossover clinical trial.

METHODS

Participants received ibudilast (20 mg twice daily followed by 50 mg twice daily) and placebo, with order determined by randomization, and then underwent intravenous methamphetamine challenges (15 and 30 mg). We monitored cardiovascular effects, methamphetamine pharmacokinetics, and reported adverse events.

RESULTS

Ibudilast treatment had similar rates of adverse events compared with placebo, and there was no significant augmentation of cardiovascular effects of methamphetamine. Pharmacokinetic analysis revealed no clinically significant change in maximum concentration or half-life of methamphetamine with ibudilast.

CONCLUSIONS

Methamphetamine administration during ibudilast treatment was well tolerated without additive cardiovascular effects or serious adverse events, providing initial safety data to pursue ibudilast's effectiveness for the treatment of methamphetamine dependence.

Relationship between discriminative stimulus effects and plasma methamphetamine and amphetamine levels of intramuscular methamphetamine in male rhesus monkeys

Methamphetamine is a globally abused drug that is metabolized to amphetamine, which also produces abuse-related behavioral effects. However, the contributing role of methamphetamine metabolism to amphetamine in methamphetamine's abuse-related subjective effects is unknown. This preclinical study was designed to determine 1) the relationship between plasma methamphetamine levels and methamphetamine discriminative stimulus effects and 2) the contribution of the methamphetamine metabolite amphetamine in the discriminative stimulus effects of methamphetamine in rhesus monkeys. Adult male rhesus monkeys (n=3) were trained to discriminate 0.18mg/kg intramuscular (+)-methamphetamine from saline in a two-key food-reinforced discrimination procedure. Time course of saline, (+)-methamphetamine (0.032-0.32mg/kg), and (+)-amphetamine (0.032-0.32mg/kg) discriminative stimulus effects were determined. Parallel pharmacokinetic studies were conducted in the same monkeys to determine plasma methamphetamine and amphetamine levels after methamphetamine administration and amphetamine levels after amphetamine administration for correlation with behavior in the discrimination procedure. Both methamphetamine and amphetamine produced full, ≥90%, methamphetamine-like discriminative stimulus effects. Amphetamine displayed a slightly, but significantly, longer duration of action than methamphetamine in the discrimination procedure. Both methamphetamine and amphetamine behavioral effects were related to methamphetamine and amphetamine plasma levels by a clockwise hysteresis loop indicating acute tolerance had developed to the discriminative stimulus effects. Furthermore, amphetamine levels after methamphetamine administration were absent when methamphetamine stimulus effects were greatest and peaked when methamphetamine discriminative stimulus effects returned to saline-like levels. Overall, these results demonstrate the methamphetamine metabolite amphetamine does not contribute to methamphetamine's abuse-related subjective effects.

The effects of varenicline on methamphetamine self-administration and drug-primed reinstatement in female rats

While research has revealed heightened vulnerability to meth addiction in women, preclinical models rarely use female subjects when investigating meth seeking and relapse. The goal of the present study was to examine the effects of varenicline (Chantix(®)), a partial α4β2 and full α7 nicotinic acetylcholine receptor agonist, on meth self-administration and reinstatement in female rats. Sprague-Dawley rats were surgically implanted with an indwelling jugular catheter. Half of the rats were then trained to self-administer meth (0.056 mg/kg/infusion) on a variable ratio 3 schedule of reinforcement; the other half earned intravenous saline during daily, 2h sessions. When responding stabilized, varenicline (0.0, 0.3, 1.0, 3.0mg/kg) was tested to determine how it altered meth taking. Varenicline was probed on 4 test days; each test separated by 2 standard self-administration sessions to assure responding remained stable. Following this testing was 15 extinction sessions. Twenty-four hours after the last extinction session were four consecutive days of meth-primed reinstatement. The same 4 doses of varenicline were examined to determine how it altered reinstatement triggered by 0.3mg/kg meth (IP). Rats readily self-administered meth. The higher doses of varenicline did not affect meth-taking in a specific fashion as active lever pressing was also slightly reduced in rats that has access to saline in the self-administration phase. Female rats displayed robust meth-primed reinstatement. Notably, the lower doses of varenicline increased meth-primed reinstatement. This amplified susceptibility to reinstatement (i.e., relapse) may be an impediment for the use of varenicline as a therapeutic to treat meth use disorder.

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.

Safety and efficacy of varenicline to reduce positive subjective effects produced by methamphetamine in methamphetamine-dependent volunteers

Methamphetamine use is increasing in the US. Although there are no Food and Drug Administration (FDA)-approved medications for methamphetamine dependence, preclinical and clinical studies suggest that methamphetamine users may benefit from treatments that enhance cholinergic neurotransmission. Consequently, we determined the safety and the efficacy of varenicline treatment, a partial agonist at α4β2 and a full agonist at α7 nicotinic acetylcholine receptors, to reduce positive subjective effects produced by smoked methamphetamine. Additionally, the effects of treatment with varenicline on the cardiovascular and reinforcing effects of methamphetamine were determined. We conducted a double-blind, placebo-controlled, within-subjects trial of varenicline vs. placebo in methamphetamine-dependent volunteers who were not seeking treatment. Participants were randomly assigned to receive one dose of varenicline (0, 1, or 2 mg) po BID, titrated up to the target dose over days 1-7, during each of three separate inpatient phases. Safety measures included the frequency, duration, severity, and relatedness of adverse events reported. Positive subjective effects included 'Any drug effect', 'High', 'Good effects', 'Stimulated', and 'Drug liking', which were rated by participants before and for 1 h after smoking methamphetamine (0, 10, and 30 mg). There were no serious adverse events and no differences in adverse events reported during the three phases. Varenicline (2 mg) significantly reduced ratings of 'Any drug effect' and 'Stimulated', as well as attenuated ratings of 'High', 'Drug liking', and 'Good effects', produced by methamphetamine (30 mg). The ability of varenicline to attenuate the positive subjective effects of methamphetamine in the laboratory suggests that varenicline should continue to be explored as a treatment for methamphetamine dependence.

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.

Pharmacotherapeutics for substance-use disorders: a focus on dopaminergic medications

INTRODUCTION

Illicit substance-use is a substantial public health concern, contributing over $150 billion in costs annually to Americans. A complex disease, a substance-use disorder affects neural circuits involved in reinforcement, motivation, learning and memory, and inhibitory control.

AREAS COVERED

The modulatory influence of dopamine in mesocorticolimbic circuits contributes to encoding the primary reinforcing effects of substances and numerous studies suggest that aberrant signaling within these circuits contributes to the development of a substance-use disorder in some individuals. Decades of research focused on the clinical development of medications that directly target dopamine receptors has led to recent studies of agonist-like dopaminergic treatments for stimulant-use disorders and, more recently, cannabis-use disorder. Human studies evaluating the efficacy of dopaminergic agonist-like medications to reduce reinforcing effects and substance-use provide some insight into the design of future pharmacotherapy trials. A search of PubMed using specific brain regions, medications, and/or the terms 'dopamine', 'cognition', 'reinforcement', 'cocaine', 'methamphetamine', 'amphetamine', 'cannabis', 'treatment/pharmacotherapy', 'addiction/abuse/dependence' identified articles relevant to this review.

EXPERT OPINION

Conceptualization of substance-use disorders and their treatment continues to evolve. Current efforts increasingly focus on a strategy fostering combination pharmacotherapies that target multiple neurotransmitter systems.

MDMA, methamphetamine, and CYP2D6 pharmacogenetics: what is clinically relevant?

In vitro human studies show that the metabolism of most amphetamine-like psychostimulants is regulated by the polymorphic cytochrome P450 isozyme CYP2D6. Two compounds, methamphetamine and 3,4-methylenedioxymethamphetamine (MDMA), were selected as archetypes to discuss the translation and clinical significance of in vitro to in vivo findings. Both compounds were chosen based on their differential interaction with CYP2D6 and their high abuse prevalence in society. Methamphetamine behaves as both a weak substrate and competitive inhibitor of CYP2D6, while MDMA acts as a high affinity substrate and potent mechanism-based inhibitor (MBI) of the enzyme. The MBI behavior of MDMA on CYP2D6 implies that subjects, irrespective of their genotype/phenotype, are phenocopied to the poor metabolizer (PM) phenotype. The fraction of metabolic clearance regulated by CYP2D6 for both drugs is substantially lower than expected from in vitro studies. Other isoenzymes of cytochrome P450 and a relevant contribution of renal excretion play a part in their clearance. These facts tune down the potential contribution of CYP2D6 polymorphism in the clinical outcomes of both substances. Globally, the clinical relevance of CYP2D6 polymorphism is lower than that predicted by in vitro studies.

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.

Toxicity of amphetamines: an update

Amphetamines represent a class of psychotropic compounds, widely abused for their stimulant, euphoric, anorectic, and, in some cases, emphathogenic, entactogenic, and hallucinogenic properties. These compounds derive from the β-phenylethylamine core structure and are kinetically and dynamically characterized by easily crossing the blood-brain barrier, to resist brain biotransformation and to release monoamine neurotransmitters from nerve endings. Although amphetamines are widely acknowledged as synthetic drugs, of which amphetamine, methamphetamine, and 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) are well-known examples, humans have used natural amphetamines for several millenniums, through the consumption of amphetamines produced in plants, namely cathinone (khat), obtained from the plant Catha edulis and ephedrine, obtained from various plants in the genus Ephedra. More recently, a wave of new amphetamines has emerged in the market, mainly constituted of cathinone derivatives, including mephedrone, methylone, methedrone, and buthylone, among others. Although intoxications by amphetamines continue to be common causes of emergency department and hospital admissions, it is frequent to find the sophism that amphetamine derivatives, namely those appearing more recently, are relatively safe. However, human intoxications by these drugs are increasingly being reported, with similar patterns compared to those previously seen with classical amphetamines. That is not surprising, considering the similar structures and mechanisms of action among the different amphetamines, conferring similar toxicokinetic and toxicological profiles to these compounds. The aim of the present review is to give an insight into the pharmacokinetics, general mechanisms of biological and toxicological actions, and the main target organs for the toxicity of amphetamines. Although there is still scarce knowledge from novel amphetamines to draw mechanistic insights, the long-studied classical amphetamines-amphetamine itself, as well as methamphetamine and MDMA, provide plenty of data that may be useful to predict toxicological outcome to improvident abusers and are for that reason the main focus of this review.

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

The effectiveness of methadone as a treatment for opioid abuse and nicotine preparations as treatments for tobacco smoking has led to an interest in developing a similar strategy for treating psychostimulant abuse. The current study investigated the effects of three such potential therapies on intravenous methamphetamine self-administration (1 - 30 μg/kg/injection) in rhesus monkeys. When given as a presession intramuscular injection, a high dose of methamphetamine (1.0 mg/kg) decreased intravenous methamphetamine self-administration but did not affect responding for a food reinforcer during the same sessions. However, the dose of intramuscular methamphetamine required to reduce intravenous methamphetamine self-administration exceeded the cumulative amount taken during a typical self-administration session, and pretreatment with a low dose of methamphetamine (0.3 mg/kg) actually increased self-administration in some monkeys at the lower self-administration dose. Like pretreatment with methamphetamine, pretreatment with bupropion (3.2 mg/kg) decreased methamphetamine self-administration but did not affect responding for food. Pretreatment with methylphenidate (0.56 mg/kg) did not significantly alter methamphetamine self-administration. These results suggest that some agonist-like agents can decrease methamphetamine self-administration. Although the most robust effects occurred with a high dose of methamphetamine, safety and abuse liability considerations suggest that bupropion should also be considered for further evaluation as a methamphetamine addiction treatment.

The clinical toxicology of metamfetamine

INTRODUCTION

Metamfetamine is a highly addictive amfetamine analog that acts primarily as a central nervous system (CNS) stimulant. The escalating abuse of this drug in recent years has lead to an increasing burden upon health care providers. An understanding of the drug's toxic effects and their medical treatment is therefore essential for the successful management of patients suffering this form of intoxication.

AIM

The aim of this review is to summarize all main aspects of metamfetamine poisoning including epidemiology, mechanisms of toxicity, toxicokinetics, clinical features, diagnosis, and management.

METHODS

A summary of the literature on metamfetamine was compiled by systematically searching OVID MEDLINE and ISI Web of Science. Further information was obtained from book chapters, relevant news reports, and web material. Epidemiology. Following its use in the Second World War, metamfetamine gained popularity as an illicit drug in Japan and later the United States. Its manufacture and use has now spread to include East and South-East Asia, North America, Mexico, and Australasia, and its world-wide usage, when combined with amfetamine, exceeds that of all other drugs of abuse except cannabis. Mechanisms of toxicity. Metamfetamine acts principally by stimulating the enhanced release of catecholamines from sympathetic nerve terminals, particularly of dopamine in the mesolimbic, mesocortical, and nigrostriatal pathways. The consequent elevation of intra-synaptic monoamines results in an increased activation of central and peripheral α±- and β-adrenergic postsynaptic receptors. This can cause detrimental neuropsychological, cardiovascular, and other systemic effects, and, following long-term abuse, neuronal apoptosis and nerve terminal degeneration. Toxicokinetics. Metamfetamine is rapidly absorbed and well distributed throughout the body, with extensive distribution across high lipid content tissues such as the blood-brain barrier. In humans the major metabolic pathways are aromatic hydroxylation producing 4-hydroxymetamfetamine and N-demethylation to form amfetamine. Metamfetamine is excreted predominantly in the urine and to a lesser extent by sweating and fecal excretion, with reported terminal half-lives ranging from ∼5 to 30 h. Clinical features. The clinical effects of metamfetamine poisoning can vary widely, depending on dose, route, duration, and frequency of use. They are predominantly characteristic of an acute sympathomimetic toxidrome. Common features reported include tachycardia, hypertension, chest pain, various cardiac dysrhythmias, vasculitis, headache, cerebral hemorrhage, hyperthermia, tachypnea, and violent and aggressive behaviour. Management. Emergency stabilization of vital functions and supportive care is essential. Benzodiazepines alone may adequately relieve agitation, hypertension, tachycardia, psychosis, and seizure, though other specific therapies can also be required for sympathomimetic effects and their associated complications.

CONCLUSION

Metamfetamine may cause severe sympathomimetic effects in the intoxicated patient. However, with appropriate, symptom-directed supportive care, patients can be expected to make a full recovery.

Pharmacological approaches to methamphetamine dependence: a focused review

Methamphetamine dependence is a serious worldwide public health problem with major medical, psychiatric, socioeconomic and legal consequences. Various neuronal mechanisms implicated in methamphetamine dependence have suggested several pharmacological approaches. A literature search from a range of electronic databases (PubMed, EMBASE, PsycInfo, the NIDA research monograph index and the reference list of clinicaltrials.gov) was conducted for the period from January 1985 to October 2009. There were no restrictions on the identification or inclusion of studies in terms of publication status, language and design type. A variety of medications have failed to show efficacy in clinical trials, including a dopamine partial agonist (aripiprazole), GABAergic agents (gabapentin) and serotonergic agents (SSRI, ondansetron, mirtazapine). Three double-blind placebo-controlled trials using modafinil, bupropion and naltrexone have shown positive results in reducing amphetamine or methamphetamine use. Two studies employing agonist replacement medications, one with d-amphetamine and the other with methylphenidate, have also shown promise. Despite the lack of success in most studies to date, increasing efforts are being made to develop medications for the treatment of methamphetamine dependence and several promising agents are targets of further research.

Evaluation of modafinil effects on cardiovascular, subjective, and reinforcing effects of methamphetamine in methamphetamine-dependent volunteers

Methamphetamine is a highly addictive stimulant and long-term exposure leads to reductions in dopamine. One therapeutic strategy is to develop and test compounds that normalize dopamine. The primary aim of this study was to determine the safety of modafinil treatment during methamphetamine exposure in a controlled clinical setting. Methamphetamine-dependent volunteers (N=13), who were not seeking treatment, were randomized to receive either modafinil (200mg, PO) or matching placebo over three days (Days 1-3 or Days 8-10). On Day 1, subjects were randomized to modafinil or placebo in the morning, and then 3 and 6h later received infusions of methamphetamine (0 and 30 mg, i.v.), after which cardiovascular and subjective effects were assessed. On Day 3, participants completed i.v. self-administration sessions during which they made 10 choices for low doses of methamphetamine (3mg, i.v.) or saline. Days 4-7 were used as a washout period. On Day 8 participants were assigned to the alternate study medication (placebo or modafinil), and the same testing procedures were repeated through Day 10. The data reveal that modafinil treatment was well-tolerated and not associated with increased incidence of adverse events. In general, modafinil reduced by approximately 25% ratings of methamphetamine-induced "Any Drug Effect", "High", and "Want Methamphetamine", and reduced total number of choices for methamphetamine and monetary value of methamphetamine, though none of these measures reached statistical significance. Given these encouraging, though non-significant trends, the primary conclusion is that it appears safe to proceed with modafinil in further clinical evaluations of therapeutic efficacy.

A review of the clinical pharmacology of methamphetamine

AIMS

To examine the literature regarding clinical pharmacokinetics, direct effects and adverse clinical outcomes associated with methamphetamine use.

METHODS

Relevant literature was identified through a PubMed search. Additional literature was obtained from relevant books and monographs.

FINDINGS AND CONCLUSIONS

The mean elimination half-life for methamphetamine is approximately 10 hours, with considerable inter-individual variability in pharmacokinetics. Direct effects at low-to-moderate methamphetamine doses (5-30 mg) include arousal, positive mood, cardiac stimulation and acute improvement in cognitive domains such as attention and psychomotor coordination. At higher doses used typically by illicit users (> or =50 mg), methamphetamine can produce psychosis. Its hypertensive effect can produce a number of acute and chronic cardiovascular complications. Repeated use may induce neurotoxicity, associated with prolonged psychiatric symptoms, cognitive impairment and an increased risk of developing Parkinson's disease. Abrupt cessation of repeated methamphetamine use leads to a withdrawal syndrome consisting of depressed mood, anxiety and sleep disturbance. Acute withdrawal lasts typically for 7-10 days, and residual symptoms associated with neurotoxicity may persist for several months.

Pavlovian drug discrimination with bupropion as a feature positive occasion setter: substitution by methamphetamine and nicotine, but not cocaine

Bupropion can serve as a discriminative stimulus (S(D)) in an operant drug discrimination task, and a variety of stimulants substitute for the bupropion S(D). There are no reports, however, of bupropion functioning as a Pavlovian occasion setter (i.e. feature positive modulator). The present experiment seeks to fill this gap in the literature by training bupropion in rats as a feature positive modulator that disambiguates when a light will be paired with sucrose. Specifically, on bupropion (10 mg/kg intraperitoneal) sessions, offset of 15-second cue lights were followed by brief delivery of liquid sucrose; saline sessions were similar except no sucrose was available. Rats readily acquired the discrimination with more conditioned responding to the light on bupropion sessions. Bupropion is approved for use as a smoking cessation aid, and more recently has drawn attention as a potential pharmacotherapy for cocaine and methamphetamine abuse. Accordingly, after discrimination training, we tested the ability of cocaine (1-10 mg/kg), methamphetamine (0.1 to 1 mg/kg) and nicotine (0.00625 to 0.2 mg/kg) to substitute for the bupropion feature. Nicotine (0.05 mg/kg) and methamphetamine (0.3 mg/kg) substituted fully for bupropion; cocaine did not substitute. These results extend previous research on shared stimulus properties between bupropion and other stimulants to a Pavlovian occasion setting function. Further, this is the first report of nicotine and methamphetamine substitution for bupropion. The overlap in stimulus properties might explain the effectiveness of bupropion as a smoking cessation aid and highlight the possible utility of bupropion for treatment of stimulant use disorder.

Bupropion attenuates methamphetamine self-administration in adult male rats

Bupropion is a promising candidate medication for methamphetamine use disorder. As such, we used a preclinical model of drug-taking to determine the effects of bupropion on the reinforcing effects of methamphetamine (0.025, 0.05 or 0.1 mg/kg/infusion). Specificity was determined by investigating the effects of bupropion on responding maintained by sucrose. In the self-administration study, rats were surgically prepared with indwelling jugular catheters and trained to self-administer methamphetamine under an FR5 schedule. A separate group of rats was trained to press a lever for sucrose. Once responding stabilized, rats were pretreated with bupropion (0, 10, 30 and 60 mg/kg i.p.) 5 min before chamber placement in a unique testing order. Following acute testing, rats were then repeatedly pretreated with 30 and 60 mg/kg bupropion. Acute treatments of bupropion dose dependently reduced drug intake for 0.025-0.1 mg/kg methamphetamine; sucrose deliveries were only reduced with the high bupropion dose. Repeated exposure to 60 mg/kg bupropion before the session resulted in a consistent decrease in methamphetamine intake (0.05 and 0.1 mg/kg) and sucrose deliveries. Considered together, this pattern of findings demonstrates that bupropion decreases responding for methamphetamine, but the effects are only somewhat specific.

Pharmacotherapy of methamphetamine addiction: an update

Methamphetamine dependence is a serious public health problem worldwide for which there are no approved pharmacological treatments. Psychotherapy is still the mainstay of treatment; however, relapse rates are high. The search for effective pharmacological treatment has intensified in the last decade. This review will highlight progress in pharmacological interventions to treat methamphetamine dependence as well as explore new pharmacological targets. Published data from clinical trials for stimulant addiction were searched using PubMed and summarized, as well as highlights from a recent symposium on methamphetamine pharmacotherapy presented at the ISAM 2006 meeting, including interim analysis data from an ongoing D-amphetamine study in Australia. Early pilot data are encouraging for administering D-amphetamine and methylphenidate as treatment for heavy amphetamine users. Abilify at 15 mg/day dose increased amphetamine use in an outpatient pilot study. Sertraline, ondansetron, baclofen, tyrosine, and imipramine were ineffective in proof-of-concept studies. Development of pharmacotherapy for methamphetamine dependence is still in an early stage. Data suggesting D-amphetamine and methylphenidate as effective pharmacotherapy for methamphetamine addiction will need to be confirmed by larger trials. Preclinical data suggest that use of GVG, CB1 antagonist, and lobeline are also promising therapeutic strategies.

Evaluation of subjective effects of aripiprazole and methamphetamine in methamphetamine-dependent volunteers

A variety of neuropharmacological strategies are being pursued in the search for an effective treatment for methamphetamine (Meth) addiction. In this study, we investigated the safety and potential efficacy of aripiprazole, an antipsychotic agent acting on both dopamine and serotonin systems. We conducted a double-blind in-patient clinical pharmacology study to assess potential interactions between intravenous (i.v.) Meth (15 mg and 30 mg) and oral aripiprazole (15 mg). In addition, the effects of aripiprazole treatment on abstinence-related craving and cue-induced craving were evaluated. Participants included non-treatment-seeking, Meth-dependent patients (n=16), aged 18-45 yr, currently using Meth. Following baseline Meth dosing (15 mg and 30 mg), participants received 2 wk treatment with aripiprazole (n=8) or placebo (n=8). Participants then completed cue exposure sessions using neutral and Meth-related cues. Meth dosing (15 mg and 30 mg) was then repeated. Aripiprazole treatment had no effect on cue-induced Meth craving, or on daily baseline craving assessed over the course of medication treatment, although aripiprazole treatment was associated with increased craving independent of Meth dosing. Aripiprazole treatment was associated with significantly higher ratings on Addiction Research Center Inventory (ARCI) subscales reflecting euphoria and amphetamine-like effects following Meth dosing. Aripiprazole treatment was also associated with significant reductions in ratings of 'bad effects' and reductions on the ARCI subscale for sedation effects following Meth dosing. Aripiprazole treatment reduced the increase in systolic blood pressure following Meth dosing, but had no other effects on cardiovascular responses to Meth. Aripiprazole treatment did not alter the pharmacokinetics of Meth. These findings indicate that aripiprazole treatment appears to be safe in volunteers with Meth dependence, although the finding that aripiprazole increased some of the rewarding and stimulatory effects produced by acute Meth suggests that 15 mg aripiprazole is unlikely to be efficacious for the treatment of Meth dependence. Further research with lower doses of aripiprazole, possibly using study designs aimed at evaluating efficacy for relapse prevention, are needed before ruling out aripiprazole as a treatment for Meth dependence.

Evaluation of the cardiovascular and subjective effects of rivastigmine in combination with methamphetamine in methamphetamine-dependent human volunteers

Acetylcholine (ACh) has been implicated in the reinforcing and locomotor-activating effects produced by methamphetamine (Meth). Of interest, recent data suggest that acetylcholinesterase (AChE) inhibitors attenuate Meth-seeking behaviour in rats. We conducted this study in order to determine the safety (adverse events, mood changes, cardiovascular effects) and preliminary efficacy (subjective effects) of the AChE inhibitor rivastigmine (Riv) when tested in combination with Meth. Twenty-three non-treatment-seeking Meth-dependent participants resided in an in-patient unit at UCLA for 2mg i.v.) and Meth (day 5, 30mg, n=7) or Riv (1.5mg, n=9). On day 11, the subjects received saline and Meth infusions again (randomized to either 11:30 or 14:30 hours), under double-blind conditions. The data analyses compared across-study measures of adverse events and mood, and a post-randomization analysis of cardiovascular and subjective effects (on day 11). The data reveal that rivastigmine was not associated with increased adverse events or alterations in mood. As expected, acute Meth exposure (30mg, significantly attenuated Meth-induced increases in diastolic blood pressure, and self-reports of and (p<0.05). Taken together, the findings in the current report suggest that pharmacological manipulations that enhance brain ACh warrant continued investigation as potential treatments for Meth addiction.

The use of bupropion SR in cigarette smoking cessation

Cigarette smoking remains the largest preventable cause of premature death in developed countries. Until recently nicotine replacement therapy (NRT) has been the only recognised form of treatment for smoking cessation. Bupropion, the first non-nicotine based drug for smoking cessation was licensed in the United States of America (US) in 1997 and in the United Kingdom (UK) in 2000 for smoking cessation in people aged 18 years and over. Bupropion exerts its effect primarily through the inhibition of dopamine reuptake into neuronal synaptic vesicles. It is also a weak noradrenalin reuptake inhibitor and has no effect on the serotonin system. Bupropion has proven efficacy for smoking cessation in a number of clinical trials, helping approximately one in five smokers to stop smoking. Up to a half of patients taking bupropion experience side effects, mainly insomnia and a dry mouth, which are closely linked to the nicotine withdrawal syndrome. Bupropion is rarely associated with seizures however care must be taken when co-prescribing with drugs that can lower seizure threshold. Also, bupropion is a potent enzyme inhibitor and can raise plasma levels of some drugs including antidepressants, antiarrhythmics and antipsychotics. Bupropion has been shown to be a safe and cost effective smoking cessation agent. Despite this, NRT remains the dominant pharmacotherapy to aid smoking cessation.

Presence and persistence of psychotic symptoms in cocaine- versus methamphetamine-dependent participants

The primary objective of this study was to compare and contrast psychotic symptoms reported by cocaine- and methamphetamine-dependent individuals. Participants included 27 cocaine-dependent and 25 methamphetamine-dependent males, as well as 15 cocaine-dependent and 18 methamphetamine-dependent females. After screening, participants were excluded if they met criteria for any Axis I diagnosis other than nicotine dependence, or methamphetamine or cocaine dependence (ie, participants had to use either methamphetamine or cocaine but were excluded if they met dependence criteria for both). The participants were administered the newly developed Psychotic Symptom Assessment Scale (PSAS), which assesses psychotic symptoms. A high proportion of both cocaine- and methamphetamine-dependent men and women reported delusions of paranoia and auditory hallucinations. However, during the abstinent and intoxicated conditions, methamphetamine-dependent men and women were more likely than cocaine-dependent men and women to report psychotic symptoms. Future studies will compare psychotic symptoms reported by non-dependent recreational stimulant users to stimulant-dependent individuals.

Bupropion for the treatment of methamphetamine dependence

Bupropion was tested for efficacy in increasing weeks of abstinence in methamphetamine-dependent patients, compared to placebo. This was a double-blind placebo-controlled study, with 12 weeks of treatment and a 30-day follow-up. Five outpatient substance abuse treatment clinics located west of the Mississippi participated in the study. One hundred and fifty-one treatment-seekers with DSM-IV diagnosis of methamphetamine dependence were consented and enrolled. Seventy-two participants were randomized to placebo and 79 to sustained-release bupropion 150 mg twice daily. Patients were asked to come to the clinic three times per week for assessments, urine drug screens, and 90-min group psychotherapy. The primary outcome was the change in proportion of participants having a methamphetamine-free week. Secondary outcomes included: urine for quantitative methamphetamine, self-report of methamphetamine use, subgroup analyses of balancing factors and comorbid conditions, addiction severity, craving, risk behaviors for HIV, and use of other substances. The generalized estimating equation regression analysis showed that, overall, the difference between bupropion and placebo groups in the probability of a non-use week over the 12-week treatment period was not statistically significant (p=0.09). Mixed model regression was used to allow adjustment for baseline factors in addition to those measured (site, gender, level of baseline use, and level of symptoms of depression). This subgroup analysis showed that bupropion had a significant effect compared to placebo, among male patients who had a lower level of methamphetamine use at baseline (p<0.0001). Comorbid depression and attention-deficit/hyperactivity disorder did not change the outcome. These data suggest that bupropion, in combination with behavioral group therapy, was effective for increasing the number of weeks of abstinence in participants with low-to-moderate methamphetamine dependence, mainly male patients, regardless of their comorbid condition.

Bupropion differentially impacts acquisition of methamphetamine self-administration and sucrose-maintained behavior

Bupropion reduces the subjective effects and cue-induced craving for methamphetamine in humans. Given these effects of bupropion on methamphetamine in humans and its widespread clinical use, a preclinical model of drug-taking was used to determine if pretreatment with bupropion would alter the acquisition of methamphetamine self-administration. During acquisition, rats were given saline or bupropion (30 or 60 mg/kg, IP) 5 min before a 60-min session. For the first 8 days, each response on the active lever produced an infusion of methamphetamine (0.025 mg/kg). Responding on the inactive lever had no programmed consequence. This FR1 schedule was then increased to an FR3 for 4 more days. In a parallel study, the identical procedures were used to test the impact of bupropion on sucrose-maintained responding. Bupropion pretreatment decreased the number of methamphetamine infusions and sucrose deliveries earned on an FR1 and FR3. However, bupropion pretreatment only delayed discrimination between the active and inactive levers in the methamphetamine self-administration rats. Discrimination between active and inactive levers was acquired in all groups in the sucrose experiment regardless of pretreatment condition. Combined, these results suggest that bupropion has a more general effect within the appetitive/reward system of the brain rather than having complete specificity for methamphetamine.

The acetylcholinesterase inhibitor rivastigmine does not alter total choices for methamphetamine, but may reduce positive subjective effects, in a laboratory model of intravenous self-administration in human volunteers

A human laboratory model of intravenous methamphetamine self-administration may facilitate study of putative treatments for methamphetamine addiction. We conducted a double-blind, placebo-controlled, between groups investigation of the acetylcholinesterase (AChE) inhibitor rivastigmine in non-treatment-seeking volunteers who met criteria for methamphetamine abuse or dependence. Safety and subjective effects data derived from days 1-10 of this protocol are described in a separate publication. In this report, we describe self-administration outcomes in participants randomized to treatment with rivastigmine (0 mg, N=7; 1.5 mg, N=6; 3 mg, N=9); data that were collected on days 11-15 of the inpatient protocol. On day 11, participants sampled two infusions of methamphetamine (0 and 30 mg, i.v.). On days 12-15, participants made ten choices each day to receive an infusion of either methamphetamine (3 mg, IV) or saline or a monetary alternative ($0.05-$16). The study design allowed for evaluation of differences in behavior on days in which infusions were performed by the physician (experimenter-administered) versus by the participant using a PCA pump (self-administered), and when monetary alternatives were presented in either ascending or descending sequence. The data show that rivastigmine (1.5 and 3 mg), as compared to placebo, did not significantly alter total choices for methamphetamine (p=0.150). Importantly, the number of infusion choices was greater when methamphetamine was available then when saline was available (p<0.0001), and the number of money choices was greater when saline was available then when methamphetamine was available (p<0.0001). The total number of choices for methamphetamine was not altered as a function of a participant's preferred route of methamphetamine use (p=0.57), and did not differ significantly whether they were experimenter-administered or self-administered (p=0.30). In addition, total choices for methamphetamine were similar made when money was available in an ascending versus descending sequence (p=0.49). The participants' years of methamphetamine use, recent use of methamphetamine (in the past 30 days), or baseline craving (indexed here as "Desire") on the day of the self-administration task were not predictive of number of choices for methamphetamine. In a subset of participants (N=8) for which data was available, individual dose of methamphetamine (3 x 3 mg, i.v.) produced significant increases in positive subjective effects, and a preliminary analysis revealed that 3 mg rivastigmine was associated with reductions in these responses, as compared to placebo. In summary, the current report indicates that there were no effects of rivastigmine on total choices for methamphetamine, that there were low levels of methamphetamine self-administration but these were 8 times greater than saline, and that choice behavior was insensitive to alternative reinforcers. In addition, we showed that rivastigmine may reduce the positive subjective effects produced by methamphetamine during self-administration.

Biological treatments for amfetamine dependence : recent progress

Amfetamine abuse has grown into a worldwide epidemic. Methamfetamine, a derivative of amfetamine made from readily accessible chemicals, has plagued the US since the 1960s, with an alarming recent surge in the numbers of those meeting the criteria for amfetamine abuse and dependence. We review this problem using a computerised literature search (PubMed 1964-2007) to summarise knowledge from animal and human studies about treatments for amfetamine dependence, while exploring the potential of pharmacogenetics to help uncover new treatment targets. Several promising therapeutic targets have come from animal models of reward, drug-taking behaviour and withdrawal. Although preclinical and selected clinical results have been promising, clinical studies have yielded inconsistent results. To improve these outcomes, pharmacogenetic studies may be used to identify candidate alleles that predict therapeutic response. Exciting preclinical findings and a steady progression of clinical results offer hope for the development of a treatment for amfetamine dependence.

Approaches to the development of medications for the treatment of methamphetamine dependence

BACKGROUND

Methamphetamine abuse has become an increasing problem in both the United States and globally with concomitant increases in adverse medical, social and environmental sequelae. Behavioral therapies have been used with some success to treat methamphetamine abusers and dependent individuals, but are not universally efficacious. Methamphetamine has a rich pharmacology that theoretically provides many opportunities for potential pharmacotherapeutic intervention. Nevertheless, there are no approved medications with an indication for treating methamphetamine abusers or addicts at this time.

AIM

To describe briefly how methamphetamine functions and affects function in brain and report how basic researchers and clinicians are attempting to exploit and exploiting this knowledge to discover and develop effective pharmacotherapies.

RESULTS

Scientifically based approaches to medications development by evaluating medications that limit brain exposure to methamphetamine; modulate methamphetamine effects at vesicular monoamine transporter-2 (VMAT-2); or affect dopaminergic, serotonergic, GABAergic, and/or glutamatergic brain pathways that participate in methamphetamine's reinforcing effects are presented.

CONCLUSION

The evidence supports the rationale that pharmacotherapies to decrease methamphetamine use, or reduce craving during abstinence may be developed from altering the pharmacokinetics and pharmacodynamics of methamphetamine or its effects on appetitive systems in the brain.

Electrocardiographic abnormalities in methamphetamine abusers

AIMS

Although many adverse cardiovascular outcomes are mentioned in conjunction with methamphetamine use, a causal relationship between methamphetamine use and arrhythmia or cardiomyopathy has not been demonstrated in man. Clinical experience with methamphetamine users suggested a higher incidence of electrocardiographic abnormalities. This study seeks to quantify that incidence, among subjects enrolled in a study of adults with methamphetamine dependence.

METHODS

Electrocardiograms obtained during screening in a previous clinical trial were examined. The study population (n = 158) of adults with methamphetamine dependence [Diagnostic and Statistical Manual version IV (DSM IV-TR)] was drawn from five sites across the United States, recruited in the interval 2002-03.

RESULTS

A significant variance from the normal population was noted in the electrocardiograms of the study cohort. Among the abnormalities was a prolongation of the QTc beyond 440 ms in 27.2% of the group. QTc prolongation to this extent poses a particular risk for ventricular arrhythmias, most notably torsades de pointes.

CONCLUSIONS

We believe that this is the first demonstration of clinically significant QTc prolongation in a methamphetamine-using population, and that this has implications for the types of arrhythmias for which this population is at risk. It may further provide a marker for risk of cardiomyopathy. The fact of electrocardiographic changes with potential cardiac risks may be useful in a motivational interviewing approach, in challenging the methamphetamine user's basis for continuing use.

Kinetic and cardiovascular effects of acute topiramate dosing among non-treatment-seeking, methamphetamine-dependent individuals

Previously, we have shown that orally administered topiramate, a sulfamate-substituted fructopyranose derivative, appears to accentuate rather than diminish some aspects of methamphetamine-induced positive subjective mood and cognitive performance. One possible mechanism by which this might occur would be for topiramate to increase plasma methamphetamine level. Such an effect also would be expected to enhance methamphetamine-induced hemodynamic response. We, therefore, studied -- in the same experiment from which the previous findings originated -- the effects of topiramate on the kinetic profile and hemodynamic response to methamphetamine. In a 27-day inpatient study, 10 methamphetamine-dependent individuals participated in a double-blind, placebo-controlled, cross-over design, with oral doses of topiramate (0, 100, and 200 mg) administered as a pretreatment before intravenous doses of methamphetamine (0, 15, and 30 mg). The 3x3 factorial combination of topiramate and methamphetamine resulted in a sequence of the nine treatments administered to each subject in an order determined by a 9x9 Latin Square design. Methamphetamine alone was associated with prototypical increases in hemodynamic response that were not altered in the presence of topiramate. While there was no significant kinetic interaction between topiramate and methamphetamine, there was a non-significant trend for topiramate to increase plasma methamphetamine level. No significant adverse events were reported. The combination of topiramate and methamphetamine at pharmacologically relevant doses appears to be safe. Larger laboratory studies with chronic dosing regimens are needed to establish whether or not there is a kinetic interaction between topiramate and methamphetamine.

Bupropion reduces methamphetamine-induced subjective effects and cue-induced craving

Bupropion is an antidepressant with stimulant properties, which inhibits the reuptake of dopamine (DA) and norepinepherine, and is purported to enhance DA neurotransmission. Bupropion is considered an appealing candidate medication for the treatment of methamphetamine dependence. The current laboratory study was set forth to assess the impact of bupropion treatment on the subjective effects produced by methamphetamine in the laboratory. We also assessed the effects of bupropion treatment on craving elicited by exposure to videotaped methamphetamine cues. A total of 26 participants were enrolled and 20 completed the entire study (n=10 placebo and n=10 bupropion, parallel groups design). Bupropion treatment was associated with reduced ratings of 'any drug effect' (p<0.02), and 'high' (p<0.02) following methamphetamine administration. There was also a significant bupropion-by-cue exposure interaction on General Craving Scale total score (p<0.002), and on the Behavioral Intention subscale (p<0.001). Overall, the data reveal that bupropion reduced acute methamphetamine-induced subjective effects and reduced cue-induced craving. Importantly, these data provide a rationale for the evaluation of bupropion in the treatment of methamphetamine dependence.

A comprehensive assessment of the safety of intravenous methamphetamine administration during treatment with selegiline

Selegiline (L-deprenyl) is a selective irreversible monoamine oxidase B inhibitor shown to be effective in the treatment of Parkinson's and Alzheimer's diseases. Recent evidence suggests that selegiline may also be useful in treating specific aspects of cocaine and nicotine dependence, generating interest in this compound for the treatment of methamphetamine addiction. To investigate this, we performed a randomized, single-blind, placebo-controlled study to evaluate the safety of selegiline treatment (as compared to placebo), concurrent with intravenous methamphetamine (15 or 30 mg). Secondary study objectives included determinations of plasma levels of selegiline and its metabolites, evaluating whether selegiline administration altered the pharmacokinetics of methamphetamine or its metabolites, and evaluating whether selegiline treatment alters the subjective responses to methamphetamine. Twenty-four methamphetamine-dependent participants were randomized to treatment, and 9 of these (N = 5 selegiline, N = 4 placebo) completed the entire protocol. The principal finding from this study was that intravenous administration of moderate doses of methamphetamine was safely tolerated during treatment with selegiline. No participants had electrocardiogram changes, and there were no meaningful differences in any laboratory values either between groups at screening or as a result of the study procedures. In general, adverse events were mild or moderate, and no subjects were discontinued due to adverse events or serious adverse events. Selegiline treatment did not enhance any of the cardiovascular changes (heart rate, blood pressure) produced by methamphetamine administration. Selegiline treatment slightly increased methamphetamine associated "bad effects" but did not alter any other subjective effects. The elimination half-life of methamphetamine was approximately 12 h, and selegiline did not alter clearance of methamphetamine. The available data suggest that selegiline is likely to be safe if used as a pharmacotherapy for methamphetamine dependence.