Discriminative-stimulus, self-reported, performance, and cardiovascular effects of atomoxetine in methylphenidate-trained humans

Effect of atomoxetine on ADHD-pain hypersensitization comorbidity in 6-OHDA lesioned mice

BACKGROUND

Methylphenidate and atomoxetine are used for the treatment of attention-deficit/hyperactivity disorder (ADHD). Our previous studies established the validity of the 6-hydroxydopamine (6-OHDA) mouse model of ADHD and demonstrated hypersensitivity to pain, in line with clinical reports in ADHD patients. Acute methylphenidate treatment reduces hyperactivity and increases attention, but does not affect pain behaviors in this mouse model. Whereas atomoxetine has been shown to be effective against some symptoms of ADHD, nothing is known about its possible action on comorbid pain hypersensitivity. The objectives of the present research are (1) to investigate the effects of acute and chronic treatment with atomoxetine on ADHD-like symptoms and nociceptive thresholds, and (2) to explore the catecholaminergic systems underlying these effects.

METHODS

Sham and 6-OHDA cohorts of male mice were tested for hyperactivity (open field), attention and impulsivity (5-choice serial reaction time task test), and thermal (hot plate test) and mechanical (von Frey test) thresholds after acute or repeated treatment with vehicle or atomoxetine (1, 3 or 10 mg/kg).

RESULTS

Acute administration of atomoxetine (10 mg/kg) reduced the hyperactivity and impulsivity displayed by 6-OHDA mice, without affecting attention or nociception. However, atomoxetine administered at 3 mg/kg/day for 7 days alleviated the ADHD-like core symptoms and attenuated the hyperalgesic responses. Furthermore, hyperlocomotion and anti-hyperalgesic activity were antagonized with phentolamine, propranolol, and sulpiride pre-treatments.

CONCLUSION

These findings demonstrated that when administered chronically, atomoxetine has a significant effect on ADHD-associated pain hypersensitization, likely mediated by both α- and β-adrenergic and D2/D3 dopaminergic receptors, and suggest new indications for atomoxetine that will need to be confirmed by well-designed clinical trials.

Individualization of attention-deficit/hyperactivity disorder treatment: pharmacotherapy considerations by age and co-occurring conditions

Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder that manifests in childhood and can persist into adolescence and adulthood. Impairments associated with ADHD can impact quality of life, social interactions, and increase the risk of morbidity and mortality; however, for many patients, effective treatment can lessen these effects. Pharmacotherapy with stimulants or nonstimulants is recommended in conjunction with psychosocial therapy for most patients. Determining the optimal pharmacotherapy can be complex, and the clinician needs to consider many factors such as the patient's age, comorbidities, and lifestyle. Furthermore, the needs of the patient with ADHD will change over time, with specific challenges to consider at each stage of life. A variety of Food and Drug Administration (FDA)-approved stimulant and nonstimulant formulations are available with different modes of delivery and durations of effect. This armamentarium of ADHD medications can be used to individualize ADHD treatment for each patient's needs. This article combines current information from the literature and the first-hand experience of the authors to provide guidance on ADHD treatment options for patients of different ages and for some of the more common comorbidities.

An update on the clinical pharmacology of methylphenidate: therapeutic efficacy, abuse potential and future considerations

INTRODUCTION

Methylphenidate remains a first-line medication for treating ADHD in children and adults. However, its behavioral pharmacological similarities to methamphetamine and cocaine have historically created concern for its potential as a drug of abuse. In September 2019, the FDA published a docket requesting comments for the development of abuse deterrent formulations for CNS stimulants, emphasizing the abuse of methylphenidate as a public health concern.

AREAS COVERED

We conducted a narrative review of research on the clinical pharmacology, therapeutic efficacy, and abuse potential of methylphenidate.

EXPERT OPINION

Several studies indicate that methylphenidate has at least some abuse potential. Methylphenidate, amphetamine, methamphetamine, and cocaine overlap in their subjective, reinforcing, and discriminative stimulus effects. Regardless, methylphenidate remains an efficacious treatment for ADHD in children and adults when properly adhered to, especially when paired with non-pharmacological treatments. The development of abuse deterrent formulations of methylphenidate is warranted.

Atomoxetine for amphetamine-type stimulant dependence during buprenorphine treatment: A randomized controlled trial

BACKGROUND

Amphetamine type stimulants (ATS) use is highly prevalent and frequently co-occurs with opioid dependence in Malaysia and Asian countries. No medications have established efficacy for treating ATS use disorder. This study evaluated the safety, tolerability, and potential efficacy of atomoxetine for treating ATS use disorder.

METHODS

Participants with opioid and ATS dependence (N = 69) were enrolled in a pilot, double-blind, placebo-controlled randomized clinical trial; all received buprenorphine/naloxone and behavioral counseling and were randomized to atomoxetine 80 mg daily (n = 33) or placebo (n = 33). The effect size of the between-group difference on the primary outcome, proportion of ATS-negative urine tests, was estimated using Cohen's d for the intention-to-treat (ITT) sample and for higher adherence subsample (≥60 days of atomoxetine or placebo ingestion).

RESULTS

Participants were all male with mean (SD) age 39.4 (6.8) years. The proportion of ATS-negative urine tests was higher in atomoxetine- compared to placebo-treated participants: 0.77 (0.63-0.91) vs. 0.67 (0.53-0.81, d = 0.26) in the ITT sample and 0.90 (0.75-1.00) vs. 0.64 (0.51-0.78, d = 0.56) in the higher adherence subsample. The proportion of days abstinent from ATS increased from baseline in both groups (p < 0.001) and did not differ significantly between atomoxetine- and placebo-treated participants (p = 0.42). Depressive symptoms were reduced from baseline in both groups (p < 0.02) with a greater reduction for atomoxetine- than placebo-treated participants (p < 0.02). There were no serious adverse events or adverse events leading to medication discontinuation.

CONCLUSIONS

The findings support clinical tolerability and safety and suggest potential efficacy of atomoxetine for treating ATS use disorder in this population.

Human drug discrimination: A primer and methodological review

Drug-discrimination procedures empirically evaluate the control that internal drug states exert over behavior. They provide a highly selective method to investigate the neuropharmacological underpinnings of the interoceptive effects of drugs. Historically, drug discrimination has been one of the most widely used assays in the field of behavioral pharmacology. Drug-discrimination procedures have also been adapted for use with humans and are conceptually similar to preclinical drug-discrimination techniques in that a behavior is differentially reinforced contingent on the presence or absence of a specific interoceptive drug stimulus. This review gives some general history and background concerning the major theoretical concepts and principles of drug-discrimination research as well as its relevance to substance-use disorders. This article also provides a procedural overview and discusses key methodological issues that must be considered when designing and conducting a human drug-discrimination study. Although drug discrimination is unequivocally one of the most sophisticated and useful behavioral assays to investigate the underlying neuropharmacology of drugs in vivo, enthusiasm for its use has steadily declined in the last decade and a half. We conclude by commenting on the current state of drug-discrimination research and suggest potential avenues for future drug-discrimination research. (PsycINFO Database Record

Influence of sensitization on the discriminative stimulus effects of methylphenidate in mice

Methylphenidate (MPH) remains an important therapy for attention-deficit hyperactivity disorder, but aspects of its pharmacology remain unclear. In the present study, we used a regimen of MPH (8 mg/kg daily×14 days) in C57BL/6J mice to determine whether establishing locomotor sensitization to MPH influenced the acquisition and the dose-response function of MPH in a classic drug discrimination procedure. MPH-sensitized mice (SENS group) showed enhanced locomotor activity to the 8 mg/kg exposure dose as well as a 2 mg/kg dose before discrimination training. However, the SENS mice did not acquire discrimination of either a low dose (2 mg/kg) or a higher dose (4 mg/kg) of MPH any more rapidly than the CTRL mice. Further, during generalization testing, the dose-response functions for the SENS and CTRL mice were identical. Therefore, we did not find that previous exposure to MPH, which produced a sensitized locomotor response, facilitated MPH discrimination.

Misuse of Methylphenidate

This chapter reviews methylphenidate misuse, abuse, dependence, diversion, and malingering associated with its use as a prescription medication for attention-deficit/hyperactivity disorder and the nonmedical use linked to its stimulant effects. Methylphenidate-induced regional elevations in brain dopamine appear to be integral to both efficacy in attention-deficit/hyperactivity disorder and potential for abuse, raising potential concerns for drug safety and prescription drug diversion costs associated with nonmedical use. Regardless, methylphenidate is an important treatment option, and detecting malingering for the purpose of illicit access to methylphenidate for subsequent misuse or diversion is a difficult challenge. Also discussed are the effects of methylphenidate in patients with comorbid substance use disorder and the potential linkage of methylphenidate use with subsequent substance abuse. The current data suggest that methylphenidate misuse and diversion are common health-care problems with a stimulant prescription drug diversion prevalence of approximately 5-10 % of high school students and 5-35 % of college students. The effectiveness and speed of action of methylphenidate are deemed desirable to enhance attention and focus performance for activities such as studying for exams, but methylphenidate is also misused recreationally. These data suggest a need for close screening and therapeutic monitoring of methylphenidate use in the treatment of attention-deficit/hyperactivity disorder.

Atomoxetine does not alter cocaine use in cocaine dependent individuals: double blind randomized trial

BACKGROUND

Cocaine abuse continues to be a significant public health problem associated with morbidity and mortality. To date, no pharmacotherapeutic approach has proven effective for treating cocaine use disorders. Preclinical and clinical evidence suggests that noradrenergic activity may play a role in mediating some effects of cocaine and may be a rational target for treatment.

METHODS

This double blind, placebo-controlled randomized, parallel group, 12-week outpatient clinical trial enrolled cocaine dependent individuals seeking treatment to examine the potential efficacy of the selective norepinephrine reuptake inhibitor, atomoxetine (80 mg/day; p.o.; n = 25), compared to placebo (n = 25). Subjects were initially stratified on cocaine use (< 15 days or ≥ 15 days of the last 30), age and race using urn randomization. Attendance, medication adherence and study compliance were reinforced with contingency management, and weekly counseling was offered. An array of measures (vital signs, laboratory chemistries, cognitive and psychomotor tests, cocaine craving and urine samples for drug testing) was collected throughout the study and at follow-up.

RESULTS

Survival analysis revealed no differences in study retention between the two groups, with approximately 56% of subjects completing the 12-week study (Cox analysis χ(2) = .72; p = .40; Hazard Ratio 1.48 [95% CI 0.62-3.39]). GEE analysis of the proportion of urine samples positive for benzoylecgonine, a cocaine metabolite, revealed no differences between the atomoxetine and placebo groups (χ(2) = 0.2, p = .66; OR = 0.89 [95% CI 0.41-1.74]). Atomoxetine was generally well tolerated in this population.

CONCLUSIONS

These data provide no support for the utility of atomoxetine in the treatment of cocaine dependence.

A review of the abuse potential assessment of atomoxetine: a nonstimulant medication for attention-deficit/hyperactivity disorder

RATIONALE

Treatment of attention-deficit/hyperactivity disorder (ADHD) has for many years relied on psychostimulants, particularly various formulations of amphetamines and methylphenidate. These are central nervous system stimulants and are scheduled because of their abuse potential. Atomoxetine (atomoxetine hydrochloride; Strattera®) was approved in 2002 for treatment of ADHD, and was the first nonstimulant medication approved for this disorder. It was classified as an unscheduled medication indicating a low potential for abuse. However, the abuse potential of atomoxetine has not been reviewed.

OBJECTIVES

In this article, we review the evidence regarding abuse potential of atomoxetine, a selective inhibitor of the presynaptic norepinephrine transporter, which is unscheduled/unrestricted in all countries where it is approved.

METHODS

Results from receptor binding, in vitro electrophysiology, in vivo microdialysis, preclinical behavioral, and human laboratory studies have been reviewed.

RESULTS

Atomoxetine has no appreciable affinity for, or action at, central receptors through which drugs of abuse typically act, i.e., dopamine transporters, GABA(A) receptors, and opioid μ receptors. In behavioral experiments in rodents, atomoxetine does not increase locomotor activity, and in drug discrimination studies, its profile is similar to that of drugs without abuse potential. Atomoxetine does not serve as a reinforcer in monkey self-administration studies, and human laboratory studies suggest that atomoxetine does not induce subjective effects indicative of abuse.

CONCLUSION

Neurochemical, preclinical, and early clinical studies predicted and supported a lack of abuse potential of atomoxetine, which is consistent with the clinical trial and postmarketing spontaneous event data in the past 10 years.

Off-label use of atomoxetine in adults: is it safe?

Atomoxetine has been approved for the treatment of attention deficit/hyperactivity disorder in both adults and children. However, it is also being examined for several off-label uses in adults including mood disorders, eating disorders, cognitive dysfunction, and the treatment of addictions. Prior to such use it is important to examine the reported adverse events to see if this represents an appropriate level of risk. This is particularly important in the light of recent warnings from several regulatory bodies about an increase in blood pressure in a significant percentage of patients taking atomoxetine. To understand the risks a literature review was performed, and which identified the following potential problems. The first is that this drug should not be given in patients with known cardiovascular problems, and that all adult patients who receive atomoxetine should be monitored for changes in blood pressure throughout treatment. Secondly, there are several clinical situations in which atomoxetine should be closely monitored, or avoided, including patients who have a history or risk of narrow angle glaucoma, epileptic seizures, Tourette's syndrome, a history of urinary outflow obstruction, or who are pregnant or lactating. In conclusion, the current literature suggests that atomoxetine can be safely used off-label provided the above precautions are taken.

Physiological and subjective effects of acute intranasal methamphetamine during atomoxetine maintenance

RATIONALE

Methamphetamine abuse and dependence are significant public-health concerns. Behavioral therapies are effective for reducing methamphetamine use. However, many patients enrolled in behavioral therapies are unable to achieve significant periods of abstinence suggesting other strategies like pharmacotherapy are needed.

OBJECTIVES

This experiment determined the physiological and subjective effects of acutely administered intranasal methamphetamine during atomoxetine maintenance in seven non-treatment seeking stimulant-dependent participants. Atomoxetine was chosen for study because it blocks reuptake at the norepinephrine transporter and increases extracellular dopamine levels in the prefrontal cortex. In this way, atomoxetine might function as an agonist replacement therapy for stimulant-dependent patients.

METHODS

After at least 7 days of maintenance on atomoxetine (0 and 80 mg/day), participants were administered ascending doses of intranasal methamphetamine (0, 5, 10, 20 and 30 mg) across two experimental sessions. Intranasal methamphetamine doses were separated by 90 min.

RESULTS

Intranasal methamphetamine produced prototypical physiological and subjective effects (e.g., increased heart rate, blood pressure, temperature and subjective ratings of Good Effects). Atomoxetine maintenance augmented the heart rate-increasing effects of methamphetamine, but attenuated the pressor effects. The subjective effects of intranasal methamphetamine were similar during atomoxetine and placebo maintenance.

CONCLUSIONS

These results suggest that methamphetamine can be safely administered to participants maintained on atomoxetine, but whether it might be an effective pharmacotherapy for methamphetamine dependence remains to be determined.

ADHD in adults: current treatment trends with consideration of abuse potential of medications

OBJECTIVE

To review the literature describing impairments in educational, occupational, and social functioning in adults with attention-deficit/hyperactivity disorder (ADHD), current treatment trends, and factors that may influence the abuse potential of long-acting medications used to treat ADHD in adults.

METHODS

A MEDLINE search was conducted to identify articles relating to functional impairments and treatment options for adults with ADHD, as well as the abuse potential of ADHD medications.

RESULTS

ADHD is one of the most common psychiatric behavioral disorders in children, and its symptoms have been shown to persist into adulthood. Symptoms of ADHD may occur at home, school, work, or in social situations, and symptom occurrence in these different settings can have a profound negative impact for adults with ADHD. Impairments in educational, occupational, and social functioning in adults with ADHD have been described and are summarized in this review article. Although long-acting medications are more frequently prescribed for children with ADHD than short-acting medications, adults with ADHD are equally likely to be treated with short- and long-acting medications. While all medications used to treat ADHD in adults have potential for abuse, there are a number of factors that may contribute to a lower potential for abuse for long-acting agents compared with immediate-release medications.

CONCLUSION

Impairments from ADHD can be chronic and persistent and they can affect daily educational, occupational, and personal functioning. Adults, in particular, have responsibilities that can extend into the late evening hours so that clinicians need to consider medication duration of action when selecting a pharmacotherapy intervention for adults with ADHD.

Conditioned place preference studies with atomoxetine in an animal model of ADHD: effects of previous atomoxetine treatment

To investigate the putative rewarding effects of atomoxetine, a non-stimulant medication for Attention-deficit/hyperactivity disorder (ADHD), we conducted conditioned place preference (CPP) tests in an animal model of ADHD, the spontaneously hypertensive rat (SHR). The effects of drug pre-exposure were also evaluated, thus, parallel experiments were done in rats which have undergone 14 days of atomoxetine treatment. The responses of SHR were compared with the rat strain representing the "normal" heterogeneous population, the Wistar rats. Neither rat strain showed significant CPP to atomoxetine. However, previous atomoxetine treatment produced place preference responses in rats, more profoundly in Wistar rats conditioned with the low and moderate atomoxetine doses. In conclusion, acute exposure to atomoxetine does not have any rewarding effect, however, drug pretreatment produces responses characteristic of reward or psychological dependence, more specifically in the "normal" vs. the ADHD animal model. The present findings call for more studies with atomoxetine, especially those that investigate the effects of long-term or chronic drug treatment.

Atomoxetine for depression and other neuropsychiatric symptoms in Parkinson disease

OBJECTIVES

Depression and antidepressant use, especially selective serotonin reuptake inhibitors (SSRIs), are common in Parkinson disease (PD). The objective of this clinical trial was to assess the efficacy of atomoxetine, a selective norepinephrine reuptake inhibitor (SNRI), for the treatment of clinically significant depressive symptoms and common comorbid neuropsychiatric symptoms in PD.

METHODS

A total of 55 subjects with PD and an Inventory of Depressive Symptomatology-Clinician (IDS-C) score > or = 22 were randomized to 8 weeks of atomoxetine or placebo treatment (target dosage = 80 mg/day). Depression response (> 50% decrease in IDS-C score or Clinical Global Impression-Improvement [CGI-I] score of 1 or 2) was assessed using intention-to-treat modeling procedures. Secondary outcomes included global cognition, daytime sleepiness, anxiety, apathy, and motor function.

RESULTS

There were no between-groups differences in a priori-defined response rates. Using a more liberal response criterion of > 40% decrease in IDS score from baseline, there was a trend (p = 0.08) favoring atomoxetine. Patients receiving atomoxetine experienced significantly greater improvement in global cognition (p = 0.003) and daytime sleepiness (p = 0.001), and atomoxetine was well-tolerated.

CONCLUSIONS

Atomoxetine treatment was not efficacious for the treatment of clinically significant depressive symptoms in PD, but was associated with improvement in global cognitive performance and daytime sleepiness. Larger studies of SNRIs in PD for disorders of mood, cognition, and wakefulness are appropriate.

CLASSIFICATION OF EVIDENCE

This interventional study provides Class II evidence that atomoxetine (target dosage = 80 mg/day) is not efficacious in improving clinically significant depression in PD.

Comparison of the behavioral and cardiovascular effects of intranasal and oral d-amphetamine in healthy human subjects

Recent reports indicate an increase in intranasal use of prescription oral stimulant medication. However, there do not appear to be any published clinical studies that have characterized the behavioral and cardiovascular effects of intranasally administered d-amphetamine, which is commonly prescribed for Attention Deficit Hyperactivity Disorder. In this study, a range of d-amphetamine doses (0, 16, 24, and 32 mg/70 kg) were administered as an intranasal solution delivered using a mucosal atomization device. Equal oral doses were included for comparison. Assessments were conducted before and at regular intervals for 3 hours following drug administration and included self-reported drug-effect questionnaires, cardiovascular indices, a performance task, and 2 measures of impulsivity. d-Amphetamine produced prototypical stimulant effects (eg, increased subject ratings of Stimulated and Like Drug, elevated heart rate and blood pressure, and improved rate and accuracy on the digit symbol substitution task) irrespective of dose, but the onset of these effects was generally earlier following intranasal administration, with significant effects emerging 15 to 30 minutes after intranasal dosing and 45 to 60 minutes after oral dosing. These results demonstrate that intranasal administration of d-amphetamine results in a more rapid onset compared to oral dosing, which could be associated with the popularity of intranasal prescription stimulant use and an enhanced potential for abuse.

Spotlight on atomoxetine in attention-deficit hyperactivity disorder in children and adolescents

Atomoxetine (Strattera) is a selective noradrenaline (norepinephrine) reuptake inhibitor that is not classified as a stimulant, and is indicated for use in patients with attention-deficit hyperactivity disorder (ADHD). Atomoxetine is effective and generally well tolerated. It is significantly more effective than placebo and standard current therapy and does not differ significantly from, or is noninferior to, immediate-release methylphenidate; however, it is significantly less effective than the extended-release methylphenidate formulation OROS methylphenidate (hereafter referred to as osmotically released methylphenidate) and extended-release mixed amfetamine salts. Atomoxetine can be administered either as a single daily dose or split into two evenly divided doses, has a negligible risk of abuse or misuse and is not a controlled substance in the US. Atomoxetine is particularly useful for patients at risk of substance abuse, as well as those who have co-morbid anxiety or tics, or who do not wish to take a controlled substance. Thus, atomoxetine is a useful option in the treatment of ADHD in children and adolescents.

Evaluation of atomoxetine for first-line treatment of newly diagnosed, treatment-naïve children and adolescents with attention deficit/hyperactivity disorder

OBJECTIVE

To test the hypothesis that first-line treatment with atomoxetine provides superior efficacy than placebo for up to 12 weeks in improving the symptoms of Attention Deficit/Hyperactivity Disorder (ADHD).

RESEARCH DESIGN AND METHODS

This double-blind, randomized, placebo-controlled, parallel clinical trial included 151 treatment-naïve children (n = 113) and adolescents (n = 38) with newly diagnosed (< or =3 months) ADHD. Atomoxetine dose was uptitrated from 0.5 to 1.2 mg/kg/day after two weeks. Outcome assessments included the ADHD Rating Scale-IV-Parent-reported Investigator-rated (ADHDRS-IV-Parent:Inv), the Clinical Global Impression of Severity of ADHD (CGI-ADHD-S), and the incidence of adverse events. Mixed-model repeated measures analysis was used to compare scale score changes between groups.

CLINICAL TRIAL REGISTRATION

Trial registered at www.clinicaltrials.gov (study internal code: B4Z-XM-LYDM, identifier: NCT00191945).

RESULTS

Most patients were male (79.2%), of caucasian origin (96.0%) and severely ill (72.5%). Their mean age was 10.3 years. Atomoxetine-treated patients showed greater reductions from baseline to week 12 of total ADHDRS-IV-Parent:Inv score than placebo-treated patients (least square mean difference: -7.9 [95% CI: -11.0 to -4.8], corresponding to a large effect size of 0.8). Between-group mean differences increased progressively with treatment exposure from week 6 to 12 (-2.7 [-4.9 to -0.6] for total and -1.6 [-2.9 to -0.3] for inattention scores). At the end of the study, 50% of atomoxetine-treated patients (14% with placebo) showed a reduction > or =40% in total ADHDRS-IV-Parent:Inv score, and only 29% (46% with placebo) were severely ill (by CGI-ADHD-S). Treatment-related adverse events were significantly more frequent with atomoxetine (65.0%) than with placebo (37.3%), the most frequent being decreased appetite and somnolence. Only one case of decreased appetite was rated as severe. No patient discontinued treatment because of adverse events.

CONCLUSIONS

A continued improvement of symptoms is expectable until 12 weeks in treatment-naïve ADHD patients treated with atomoxetine as first-line medication. Chief limitations are the small, national sample size and the absence of data beyond the 12-week time-point.

The neuropharmacology of ADHD drugs in vivo: insights on efficacy and safety

Results from in vivo techniques, especially intracerebral microdialysis in freely-moving rats, have provided insights into potential mechanisms responsible for the efficacy and safety of catecholaminergic drugs for ADHD treatment. The drugs reviewed come from distinct pharmacological classes: psychostimulant releasing agents, eg d-amphetamine; psychostimulant reuptake inhibitors, eg dl-threo-methylphenidate (dl-MPH), and non-stimulant reuptake inhibitors, eg atomoxetine. Psychostimulants, which currently deliver the best efficacy in treating ADHD, exhibit the following characteristics on extraneuronal catecholamine concentrations in rodent brain in vivo: 1) They enhance the efflux and function of both noradrenaline and dopamine in the central nervous system. 2) The increase of dopamine efflux that they produce is not limited to cortical regions. 3) They have a rapid onset of action with no ceiling on drug effect. d-Amphetamine has a mechanism independent of neuronal firing rate, displacing intraneuronal stores of catecholamines, delaying their reuptake and inhibiting catabolism by monoamine oxidase. dl-MPH has an enigmatic, extraneuronal action that is neuronal firing rate-dependent and reuptake transporter-mediated, yet paradoxically, almost as powerful as that of d-amphetamine. In safety terms, these powerful catecholaminergic effects also make the psychostimulants liable for abuse. Since efficacy and safety derive from the same pharmacological mechanisms, it has not yet been possible to separate these two components. However, the development of once-daily psychostimulant formulations and a prodrug, lisdexamfetamine, has improved patient compliance and markedly reduced scope for their diversion/abuse. This review will discuss the in vivo pharmacological profiles of approved catecholaminergic drugs for treatment of ADHD and implications for their clinical efficacy and abuse liability.

Atomoxetine: a review of its use in attention-deficit hyperactivity disorder in children and adolescents

Atomoxetine (Strattera(R)) is a selective norepinephrine (noradrenaline) reuptake inhibitor that is not classified as a stimulant, and is indicated for use in patients with attention-deficit hyperactivity disorder (ADHD). Atomoxetine is effective and generally well tolerated. It is significantly more effective than placebo and standard current therapy and does not differ significantly from or is noninferior to immediate-release methylphenidate; however, it is significantly less effective than the extended-release methylphenidate formulation OROS(R) methylphenidate (hereafter referred to as osmotically released methylphenidate) and extended-release mixed amfetamine salts. Atomoxetine can be administered either as a single daily dose or split into two evenly divided doses, has a negligible risk of abuse or misuse, and is not a controlled substance in the US. Atomoxetine is particularly useful for patients at risk of substance abuse, as well as those who have co-morbid anxiety or tics, or who do not wish to take a controlled substance. Thus, atomoxetine is a useful option in the treatment of ADHD in children and adolescents. The mechanism of action of atomoxetine is unclear, but is thought to be related to its selective inhibition of presynaptic norepinephrine reuptake in the prefrontal cortex. Atomoxetine has a high affinity and selectivity for norepinephrine transporters, but little or no affinity for various neurotransmitter receptors. Atomoxetine has a demonstrated ability to selectively inhibit norepinephrine uptake in humans and animals, and studies have shown that it preferentially binds to areas of known high distribution of noradrenergic neurons, such as the fronto-cortical subsystem. Atomoxetine was generally associated with statistically, but not clinically, significant increases in both heart rate and blood pressure in pediatric patients with ADHD. While there was an initial loss in expected height and weight among atomoxetine recipients, this eventually returned to normal in the longer term. Data suggest that atomoxetine is unlikely to have any abuse potential. Atomoxetine appeared less likely than methylphenidate to exacerbate disordered sleep in pediatric patients with ADHD. Atomoxetine is rapidly absorbed, and demonstrates dose-proportional increases in plasma exposure. It undergoes extensive biotransformation, which is affected by poor metabolism by cytochrome P450 (CYP) 2D6 in a small percentage of the population; these patients have greater exposure to and slower elimination of atomoxetine than extensive metabolizers. Patients with hepatic insufficiency show an increase in atomoxetine exposure. CYP2D6 inhibitors, such as paroxetine, are associated with changes in atomoxetine pharmacokinetics similar to those observed among poor CYP2D6 metabolizers. Once- or twice-daily atomoxetine was effective in the short-term treatment of ADHD in children and adolescents, as observed in several well designed placebo-controlled trials. Atomoxetine also demonstrated efficacy in the longer term treatment of these patients. A single morning dose was shown to be effective into the evening, and discontinuation of atomoxetine was not associated with symptom rebound. Atomoxetine efficacy did not appear to differ between children and adolescents. Stimulant-naive patients also responded well to atomoxetine treatment. Atomoxetine did not differ significantly from or was noninferior to immediate-release methylphenidate in children and adolescents with ADHD with regard to efficacy, and was significantly more effective than standard current therapy (any combination of medicines [excluding atomoxetine] and/or behavioral counseling, or no treatment). However, atomoxetine was significantly less effective than osmotically released methylphenidate and extended-release mixed amfetamine salts. The efficacy of atomoxetine did not appear to be affected by the presence of co-morbid disorders, and symptoms of the co-morbid disorders were not affected or were improved by atomoxetine administration. Health-related quality of life (HR-QOL) appeared to be positively affected by atomoxetine in both short- and long-term studies; atomoxetine also improved HR-QOL to a greater extent than standard current therapy. Atomoxetine was generally well tolerated in children and adolescents with ADHD. Common adverse events included headache, abdominal pain, decreased appetite, vomiting, somnolence, and nausea. The majority of adverse events were mild or moderate; there was a very low incidence of serious adverse events. Few patients discontinued atomoxetine treatment because of adverse events. Atomoxetine discontinuation appeared to be well tolerated, with a low incidence of discontinuation-emergent adverse events. Atomoxetine appeared better tolerated among extensive CYP2D6 metabolizers than among poor metabolizers. Slight differences were evident in the adverse event profiles of atomoxetine and stimulants, both immediate- and extended-release. Somnolence appeared more common among atomoxetine recipients and insomnia appeared more common among stimulant recipients. A black-box warning for suicidal ideation has been published in the US prescribing information, based on findings from a meta-analysis showing that atomoxetine is associated with a significantly higher incidence of suicidal ideation than placebo. Rarely, atomoxetine may also be associated with serious liver injury; postmarketing data show that three patients have had liver-related adverse events deemed probably related to atomoxetine treatment. Treatment algorithms involving the initial use of atomoxetine appear cost effective versus algorithms involving initial methylphenidate (immediate- or extended-release), dexamfetamine, tricyclic antidepressants, or no treatment in stimulant-naive, -failed, and -contraindicated children and adolescents with ADHD. The incremental cost per quality-adjusted life-year is below commonly accepted cost-effectiveness thresholds, as shown in several Markov model analyses conducted from the perspective of various European countries, with a time horizon of 1 year.

Substitution profile of Delta9-tetrahydrocannabinol, triazolam, hydromorphone, and methylphenidate in humans discriminating Delta9-tetrahydrocannabinol

RATIONALE

Preclinical evidence suggests that non-cannabinoid neurotransmitter systems are involved in the behavioral and physiological effects of cannabinoids, but relatively little research has been conducted in humans.

OBJECTIVES

The aims of this study were to assess whether oral Delta(9)-tetrahydrocannabinol (Delta(9)-THC) would function as a discriminative stimulus in humans and to examine the substitution profile of drugs acting at opioid, GABA, and dopamine systems.

METHODS

Healthy subjects who reported moderate cannabis use were enrolled. Subjects learned to identify when they received oral 25 mg Delta(9)-THC or placebo under double-blind conditions. Once subjects acquired the discrimination (i.e., > or =80% drug-appropriate responding for four consecutive sessions), multiple doses of Delta(9)-THC, the GABA(A) positive modulator triazolam, the micro-opioid agonist hydromorphone and the dopamine reuptake inhibitor methylphenidate were tested to determine if they shared discriminative-stimulus effects with the training dose of Delta(9)-THC.

RESULTS

Eight subjects (N = 8) accurately discriminated Delta(9)-THC and completed the study. The training dose of Delta(9)-THC functioned as a discriminative stimulus and produced prototypical subject-rated drug effects. All of the drugs tested produced significant effects on the self-report questionnaires, but only Delta(9)-THC substituted for the training dose.

CONCLUSION

These results suggest that the discriminative-stimulus effects of Delta(9)-THC in humans are not directly mediated through central neurotransmitter systems acted upon by the drugs tested in this study.

Discriminative stimulus and subject-rated effects of methamphetamine, d-amphetamine, methylphenidate, and triazolam in methamphetamine-trained humans

Methamphetamine abuse is a significant public health concern. Although widely studied in laboratory animals, little is known about the abuse-related behavioral effects of methamphetamine relative to other abused stimulants in controlled laboratory settings in humans. The aim of this study was to examine the discriminative stimulus, subject-rated, performance, and cardiovascular effects of methamphetamine in humans. In the present study, subjects first learned to discriminate 10 mg of oral methamphetamine from placebo. After acquiring the discrimination (> or = 80% drug-appropriate responding on four consecutive sessions), a range of oral doses of methamphetamine (2.5-15 mg), d-amphetamine (2.5-15 mg), methylphenidate (5-30 mg), and triazolam (0.0625-0.375 mg) was tested. Methamphetamine functioned as a discriminative stimulus and produced prototypical stimulant-like subject-rated effects. d-Amphetamine and methylphenidate produced dose-related increases in methamphetamine-appropriate responding, whereas triazolam did not. d-Amphetamine and methylphenidate produced stimulant-like behavioral effects, whereas triazolam produced sedative-like effects. Methamphetamine, but no other drug, increased heart rate, systolic pressure, and diastolic pressure significantly above placebo levels. Performance in the Digit-Symbol Substitution Test was not affected by any of the drugs tested. Overall, these results demonstrate that the acute behavioral effects of methamphetamine, d-amphetamine, and methylphenidate overlap extensively in humans, which is concordant with findings from preclinical studies. Future studies should assess whether the similarity in the behavioral effects of methamphetamine and related stimulants can be extended to other behavioral assays, such as measures of reinforcement, in humans.

ADHD, substance use disorders, and psychostimulant treatment: current literature and treatment guidelines

OBJECTIVE

This review explores the relationship between ADHD and substance use disorder (SUD), factors that determine the abuse potential of psychostimulants, and strategies for identifying and treating at-risk ADHD patients.

METHOD

This study uses a Medline review of literature.

RESULTS

Psychostimulants, such as methylphenidate and amphetamines, are effective first-line pharmacotherapy for ADHD and when used appropriately in individuals with ADHD do not appear to be frequently abused by patients. Diversion and misuse of prescription stimulants are growing concerns, especially among young adults and college students. Short-acting psychostimulant formulations may have higher potential for abuse, misuse, and diversion, but more data are needed to substantiate this observation. Nonstimulant treatments for ADHD may be considered for patients at particularly high risk for substance use, misuse, or diversion of stimulants.

CONCLUSION

In treating patients with ADHD and comorbid substance use, psychostimulants may be a useful pharmacologic alternative. However, the risks of such treatment with high-risk populations must be considered alongside potential benefits.

Abuse liability assessment of atomoxetine in a drug-abusing population

BACKGROUND

Atomoxetine is a non-amphetamine medication approved to treat ADHD in children, adolescents, and adults. Previous studies demonstrated low abuse potential for atomoxetine in recreational drug users. This study assessed the abuse potential of atomoxetine in stimulant-preferring drug abusers compared to methylphenidate and phentermine as positive controls and desipramine and placebo as negative controls.

METHODS

Forty male and female, 32-53 years old stimulant-preferring drug abusers completed this balanced Latin-square designed study. Subjects received acute, double-blind doses of placebo, desipramine (100 and 200 mg), methylphenidate (90 mg), phentermine (60 mg), and atomoxetine (45, 90, and 180 mg). Subjective and physiological effects were collected for 24 h following each drug treatment.

RESULTS

Methylphenidate and phentermine were liked significantly more than placebo, atomoxetine, or desipramine. No atomoxetine dose was liked significantly more than placebo and liking scores for atomoxetine were similar to, or significantly lower than, desipramine, as assessed by the Drug Rating Questionnaire-Subject. While atomoxetine 45 and 180 mg did not significantly change any Addiction Research Center Inventory (ARCI) scores, atomoxetine 90 mg significantly increased A and BG stimulant scores of the ARCI and both methylphenidate and phentermine produced greater A and BG increases than any atomoxetine dose and also increased MBG (euphoria) scores relative to placebo.

CONCLUSIONS

Atomoxetine has significantly less abuse liability than methylphenidate or phentermine and no greater abuse liability than desipramine.

A qualitative review of issues arising in the use of psycho-stimulant medications in patients with ADHD and co-morbid substance use disorders

OBJECTIVE

This review addresses the relationship between attention-deficit/hyperactivity disorder (ADHD) and substance use disorders (SUDs), with an emphasis on factors that determine the potential for psychostimulant abuse. Strategies for identification and treatment of patients with ADHD who are at risk for, or have, co-morbid SUD are also addressed.

RESEARCH DESIGN AND METHODS

The article was based on a qualitative review of current literature addressing co-morbid ADHD and SUD.

DISCUSSION

Adolescent and adult patients with ADHD are at increased risk for SUD, as well as a number of other psychiatric disorders. Psychostimulant agents like methylphenidate (MPH) and mixed amphetamine salts (MAS) are effective first-line pharmacotherapies for ADHD; however, they are Schedule II controlled substances with a potential for abuse. Evidence suggests that treatment of ADHD during childhood with stimulant agents may reduce the risk of developing SUD later on. Factors associated with the highest risk of SUD in patients with ADHD include co-morbid antisocial personality disorder, bipolar disorder, an eating disorder, severe ADHD and/or antisocial behavior symptoms, and dropping out of school. Treatment initiation during adolescence or young adulthood also has been linked to increased risk of polydrug use and non-medical stimulant use, a pattern of behavior consistent with a risk of SUD development. Treatment plans for patients with ADHD and co-morbid SUD should include behavioral interventions, careful monitoring, and when appropriate, pharmacotherapy. When oral formulations of psychostimulants are used at recommended doses and frequencies, they are unlikely to yield effects consistent with abuse potential in patients with ADHD. Long-acting stimulant formulations and non-stimulants, like atomoxetine or bupropion, have a lower potential for abuse, and provide several safe and effective treatment options for the development of a comprehensive management plan for patients with co-morbid ADHD and SUD.

CONCLUSIONS

The present review is neither exhaustive nor systematic. Moreover, the reviewed studies vary widely with regards to methodology and patient populations. In light of these limitations, several conclusions are still warranted. Patients with ADHD are at increased risk for SUD. Under certain conditions, psychostimulants may be a pharmacologic option in the treatment of patients with co-morbid ADHD and SUD. However, clinicians should be mindful of the risks and benefits of this treatment approach in a high-risk population and should also bear in mind the labeling guidelines when working with this co-morbidity.

Safety, tolerability and subject-rated effects of acute intranasal cocaine administration during atomoxetine maintenance

The results of recent research indicate that agonist replacement may be a viable option in the treatment of cocaine dependence. For example, d-amphetamine and modafinil have shown promise in managing cocaine dependence in preliminary clinical trials. The aim of this study was to determine the physiological and subject-rated effects of acute intranasal cocaine doses during chronic atomoxetine treatment. Atomoxetine was chosen because it produces pharmacological and subject-rated effects similar to those of prototypical stimulants and thus may also be a viable agonist replacement therapy. To this end, seven cocaine-dependent subjects were maintained on doses of atomoxetine (0mg [lead in], 5, 10, 20 and 0mg [washout], four times daily) for 3-5 days prior to completing experimental sessions in which ascending doses of intranasal cocaine (4, 20, 40 and 60 mg) were administered. Cocaine produced prototypical cardiovascular and subject-rated effects. Atomoxetine attenuated the systolic pressure increasing effects and enhanced the heart rate increasing effects of cocaine, but was otherwise devoid of effects. These results indicate that cocaine is well tolerated during atomoxetine maintenance. Further research is needed to better determine the effects of atomoxetine and cocaine combinations.

A pharmacological analysis of stimulant-induced increases in smoking

RATIONALE

Stimulants increase tobacco smoking in healthy adults under controlled laboratory conditions. The mechanisms that mediate stimulant-induced increases in smoking are not known.

OBJECTIVE

The purpose of the present experiment was to characterize the pharmacological specificity of stimulant-induced increases in smoking. We tested the effects of methylphenidate and atomoxetine on smoking behavior. Atomoxetine is a norepinephrine transport inhibitor that does not increase dopamine levels in the nucleus accumbens or striatum. If stimulant-induced increases in smoking result from an additive or synergistic effect of these drugs and nicotine on dopamine levels in the nucleus accumbens or striatum, methylphenidate but not atomoxetine should increase smoking.

MATERIALS AND METHODS

Doses of methylphenidate (10, 20, and 40 mg) and atomoxetine (20, 40, and 80 mg) were tested once while placebo was tested twice in 12 cigarette smokers. One hour after ingesting drug, participants smoked ad libitum for 4 h. Measures of smoking included total cigarettes, total puffs, and carbon monoxide levels. Snacks and decaffeinated drinks were available ad libitum, and food intake was calculated.

RESULTS

Methylphenidate but not atomoxetine dose-dependently increased the number of cigarettes, puffs, and carbon monoxide levels. Methylphenidate and atomoxetine decreased food intake.

CONCLUSIONS

The results of this experiment are consistent with the notion that stimulant-induced increases in smoking may result from an additive or synergistic effect of these drugs and nicotine on dopamine levels in the nucleus accumbens or striatum. Additional research is needed to more fully understand the pharmacological mechanisms that mediate the relationship between stimulant use and smoking.

Atomoxetine increases salivary cortisol in healthy volunteers

It has been proposed that acute hypothalamo-pituitary-adrenal (HPA) axis challenge using noradrenergic drugs may be of utility in assessing the functional integrity of central noradrenaline pathways. Atomoxetine (formerly tomoxetine) is a highly selective noradrenaline reuptake inhibitor, which has recently been licensed for the treatment of attention deficit hyperactivity disorder (ADHD). The aim of this study was to assess the effects of acute atomoxetine on salivary cortisol levels for the first time.A total of 60 healthy male volunteers received 60 mg atomoxetine, 30 mg citalopram, or placebo per os in a double-blind parallel groups design (n = 20 per group). Salivary cortisol, blood pressure and pulse rates were recorded at baseline and at +1.0, +1.5, +2.5 and +3.5 hours after capsule administration.60 mg atomoxetine led to highly significant increases in salivary cortisol and a moderate increase in pulse rate, in the absence of significant effects on blood pressure. 30 mg citalopram had no significant effects on cortisol or cardiovascular parameters. These data support the utility of atomoxetine neuroendocrine challenge for evaluating central noradrenaline pathways, which may be of future use in neuropsychiatric patient studies. Furthermore, the effects of atomoxetine on HPA axis function may have clinical implications given the use of this agent in the treatment of ADHD.