Common and Unique Therapeutic Mechanisms of Stimulant and Nonstimulant Treatments for Attention-Deficit/Hyperactivity Disorder
CONTEXT Attention-deficit/hyperactivity disorder (ADHD) is a highly prevalent and impairing psychiatric disorder that affects both children and adults. There are Food and Drug Administration-approved stimulant and nonstimulant medications for treating ADHD; however, little is known about the mechanisms by which these different treatments exert their therapeutic effects. OBJECTIVE To contrast changes in brain activation related to symptomatic improvement with use of the stimulant methylphenidate hydrochloride vs the nonstimulant atomoxetine hydrochloride. DESIGN Functional magnetic resonance imaging before and after 6 to 8 weeks of treatment with methylphenidate (n = 18) or atomoxetine (n = 18) using a parallel-groups design. SETTING Specialized ADHD clinical research program at Mount Sinai School of Medicine, New York, New York. PARTICIPANTS Thirty-six youth with ADHD (mean [SD] age, 11.2 [2.7] years; 27 boys) recruited from randomized clinical trials. MAIN OUTCOME MEASURES Changes in brain activation during a go/no-go test of response inhibition and investigator-completed ratings on the ADHD Rating Scale-IV-Parent Version. RESULTS Treatment with methylphenidate vs atomoxetine was associated with comparable improvements in both response inhibition on the go/no-go test and mean (SD) improvements in ratings of ADHD symptoms (55% [30%] vs 57% [25%]). Improvement in ADHD symptoms was associated with common reductions in bilateral motor cortex activation for both treatments. Symptomatic improvement was also differentially related to gains in task-related activation for atomoxetine and reductions in activation for methylphenidate in the right inferior frontal gyrus, left anterior cingulate/supplementary motor area, and bilateral posterior cingulate cortex. These findings were not attributable to baseline differences in activation. CONCLUSIONS Treatment with methylphenidate and atomoxetine produces symptomatic improvement via both common and divergent neurophysiologic actions in frontoparietal regions that have been implicated in the pathophysiology of ADHD. These results represent a first step in delineating the neurobiological basis of differential response to stimulant and nonstimulant medications for ADHD.
Available from: Tai-Li Chou
- "Our finding is in agreement with findings from Bush et al. (2008) that utilized interference task that requires numbering process as well. Despite a consistently reported increase of striatal activation among patients with ADHD by a single dose methylphenidate treatment (Cubillo et al., 2014b; Rubia et al., 2011), present results lacking of striatal activation changes are not surprising because our results are in agreement with studies addressing effect of weeks of methylphenidate treatment (Bush et al., 2008; Schulz et al., 2012). Similar observations were reported in rodent models following 14-day treatment of methylphenidate. "
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ABSTRACT: Methylphenidate and atomoxetine are effective in treating attention-deficit/hyperactivity disorder (ADHD) with underlying distinct pharmacological mechanisms. To relate neural mechanisms to clinical response, we conducted a comparative trial to differentiate the changes in brain activation of drug-naïve children with ADHD when performing neuropsychological tasks after 12 weeks of pharmacotherapy. We randomized 50 drug-naïve children with ADHD, aged 7-17, to treatment with methylphenidate (n=25) or atomoxetine (n=25). These children were scanned twice with functional magnetic resonance imaging (fMRI) during the counting Stroop task before and after treatment. Focused attention and impulsivity were assessed twice by using the Conner's Continuous Performance Test (CCPT). The final sample for fMRI analysis comprised 20 in the methylphenidate group and 22 in the atomoxetine group. Atomoxetine decreased activations in the dorsal anterior cingulate cortex and dorsolateral prefrontal cortex, which correlated with improvement in focused attention assessed by the CCPT. In contrast, methylphenidate increased activations in the inferior frontal gyrus, which correlated with the decreasing severity of impulsivity assessed by the CCPT. The current findings suggest that differential therapeutic effects on neuronal changes induced by 12-week treatment atomoxetine and methylphenidate may contribute to behavioral improvement.
European neuropsychopharmacology: the journal of the European College of Neuropsychopharmacology 09/2015; DOI:10.1016/j.euroneuro.2015.08.024 · 4.37 Impact Factor
Available from: Cesar A Soutullo
- "These differential effects could potentially contribute to the differences in relapse seen across treatment types, but the specific manner in which differential activation of brain regions leads to these clinical changes is not clear. Interestingly, even though both MPH and ATX were associated with similar improvements in ADHD symptoms and response inhibition on the go/no-go test, there were differential activations in the right inferior frontal gyrus, left anterior cingulate, supplementary motor area, and bilateral posterior cingulate cortex (Schulz et al, 2012). "
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ABSTRACT: The attention-deficit/hyperactivity disorder (ADHD) treatment literature has been focused on onset-of-effect and short-term effect size, with little exploration of ADHD symptoms upon medication discontinuation. The objective of this narrative review and analysis was to better understand the relapse of ADHD symptoms upon discontinuation of medication treatment in children, adolescents, and adults with ADHD who have responded to medication treatment and to explore differences among different medications in maintaining treatment response. Randomized withdrawal studies of dexmethylphenidate hydrochloride (d-MPH), methylphenidate modified-release (MPH-LA), lisdexamphetamine dimesylate (LDX), guanfacine extended-release (GXR), and atomoxetine (ATX) in both children/adolescents and adults with ADHD were reviewed. The percentage of relapse was significantly higher and the time-to-relapse significantly shorter with placebo compared to active treatment in patients who were previously stable on 5 weeks to 1 year of active treatment, suggesting clinically significant benefit with continued long-term pharmacotherapy. However, percentage of relapse at each time point studied after discontinuing stimulants and GXR appears substantially higher than observed when discontinuing ATX, suggesting longer maintenance of response after discontinuing ATX than after stimulants and GXR. Additionally, slope of relapse percentages over time appears to be more rapid with stimulants or GXR than with ATX. These differences in maintenance of response among ATX, GXR, and stimulants may reflect differences in mechanisms of action and persistence of the medication effect. Alternatively, they may be due to methodological differences, including study design and response/relapse definitions. Continued investigation is needed regarding factors that affect risk of symptom relapse upon discontinuation of pharmacotherapy.
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European neuropsychopharmacology: the journal of the European College of Neuropsychopharmacology 06/2015; 14(10). DOI:10.1016/j.euroneuro.2015.06.003 · 4.37 Impact Factor
Available from: Mark A Stein
- "This study tested whether ATX and MPH improve performance on purported laboratory measures of attention and inhibitory control as assessed by Conners' CPT-II. It was hypothesized that performance on the Conners' CPT-II would be improved by both treatments, but the nature and/or magnitude of response might differ by drug – based on data suggesting that the two medications work via somewhat different mechanisms (Schulz et al., 2012). We also hypothesized that ATX would produce smaller improvements on the Conners' CPT-II than MPH at the group level, based on the limited comparator data available to date (e.g., Yildiz et al., 2011). "
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ABSTRACT: This study examined the effects of atomoxetine (ATX) and OROS methylphenidate (MPH) on laboratory measures of inhibitory control and attention in youth with attention-deficit/hyperactivity disorder (ADHD). It was hypothesized that performance would be improved by both treatments, but response profiles would differ because the medications work via different mechanisms. One hundred and two youth (77 male; mean age = 10.5 ± 2.7 years) with ADHD received ATX (1.4 ± 0.5 mg/kg) and MPH (52.4 ± 16.6 mg) in a randomized, double-blind, crossover design. Medication was titrated in 4–6-week blocks separated by a 2-week placebo washout. Inhibitory control and attention measures were obtained at baseline, following washout, and at the end of each treatment using Conners' Continuous Performance Test II (CPT-II), which provided age-adjusted T-scores for reaction time (RT), reaction time variability (RT variability), and errors. Repeated-measures analyses of variance were performed, with Time (premedication, postmedication) and Treatment type (ATX, MPH) entered as within-subject factors. Data from the two treatment blocks were checked for order effects and combined if order effects were not present. Clinical trial registration: Clinicaltrials.gov: NCT00183391. Main effects for Time on RT (p = .03), RTSD (p = .001), and omission errors (p = .01) were significant. A significant Drug × Time interaction indicated that MPH improved RT, RTSD, and omission errors more than ATX (p < .05). Changes in performance with treatment did not correlate with changes in ADHD symptoms. MPH has greater effects than ATX on CPT measures of sustained attention in youth with ADHD. However, the dissociation of cognitive and behavioral change with treatment indicates that CPT measures cannot be considered proxies for symptomatic improvement. Further research on the dissociation of cognitive and behavioral endpoints for ADHD is indicated.
Journal of Child Psychology and Psychiatry 06/2014; 56(1). DOI:10.1111/jcpp.12272 · 6.46 Impact Factor
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