Clinically Relevant Doses of Methylphenidate Significantly Occupy the Norepinephrine Transporter in Humans In VivoJonas Hannestad, M.D., Ph.D., Jean-Dominique Gallezot, Ph.D., [...], and Yu-Shin Ding, Ph.D.Additional article informationAssociated DataSupplementary MaterialsAbstractBackgroundAttention Deficit Hyperactivity Disorder (ADHD) is a psychiatric disorder that starts in childhood. The mechanism of action of methylphenidate (MPH), the most common treatment for ADHD, is unclear. In vitro, the affinity of MPH for the norepinephrine transporter (NET) is higher than that for the dopamine transporter (DAT). The goal of this study was to use Positron Emission Tomography to measure the occupancy of NET by MPH in vivo in humans.MethodsWe used (S,S)-[11C]methylreboxetine ([11C]MRB) to determine the Effective Dose 50 (ED50) of MPH for NET. In a within-subject design, healthy subjects (n=11) received oral, single-blind placebo and 2.5 mg, 10 mg, and 40 mg of MPH 75 minutes prior to [11C]MRB injection. Dynamic PET imaging was performed for 2 hrs with the High Resolution Research Tomograph. The multilinear reference tissue model with occipital cortex as the reference region was used to estimate binding potential (BPND) in the thalamus and other NET-rich regions.ResultsBPND was reduced by MPH in a dose-dependent manner in thalamus and other NET-rich regions. The global ED50 was estimated to be 0.14 mg/kg, therefore the average clinical maintenance dose of MPH (0.35–0.55 mg/kg) produces 70–80% occupancy of NET.ConclusionsFor the first time in humans, we demonstrate that oral MPH significantly occupies NET at clinically relevant doses. The ED50 is lower than that for DAT (0.25 mg/kg), suggesting the potential relevance of NET inhibition in the therapeutic effects of MPH in ADHD.Keywords: Attention Deficit Hyperactivity Disorder, Methylphenidate, Norepinephrine transporter, Dopamine, [11C]methylreboxetine, Positron Emission TomographyIntroductionThe core features of Attention Deficit Hyperactivity Disorder (ADHD) - inattention, hyperactivity, and impulsivity - can be attributed to dysfunction in neural systems that regulate attention, executive function, motor control, and reward (1, 2)(3). The three classes of pharmacologic treatments for