Assessment of effects of atomoxetine in adult patients with ADHD: consistency among three geographic regions in a response maintenance study.

A previous study (Upadhyaya et al. in Eur J Psychiatry 2013b; 27:185-205) reported that adults with attention-deficit/hyperactivity disorder (ADHD) demonstrated maintenance of response for up to 25 weeks after initially responding to atomoxetine treatment. In the present report, the consistency of treatment effect across three geographic regions (Europe, United States/Canada [US/Can], and Latin America [Latin Am]) was explored. Data were analyzed from a phase 3, multicenter, randomized, double-blind, maintenance-of-response (randomized withdrawal) trial of atomoxetine versus placebo in adults with ADHD. Patients were randomized to atomoxetine (N = 266) or placebo (N = 258) for 25 weeks. Consistency assessments included the interaction test, pairwise t tests, noninferiority, and the criteria from Basic Principles on Global Clinical Trials (Ministry of Health, Labour and Welfare of Japan 2007). Atomoxetine-treated patients maintained the improved ADHD symptoms relative to placebo-treated patients on the Conners' Adult ADHD Rating Scale Investigator-Rated: Screening Version 18-Item (CAARS-Inv:SV) total score in all three regions (atomoxetine-placebo mean difference = -4.55, -3.18, and -0.07 for Europe, US/Can, and Latin Am, respectively). For the Latin Am region, the mean change in total score (0.41) was notably smaller for the placebo group than for Europe (5.87) and US/Can (4.39). Similar results were observed for the CAARS-Inv:SV hyperactivity/impulsivity and inattention subscale scores. Overall, patients maintained the response with atomoxetine treatment compared to placebo; however, the magnitude of treatment effect differed among the regions studied, being numerically higher in the EU and US/Can than Latin Am. Trial registration http://www.clinicaltrials.gov/(NCT00700427 ).