Safety of Methylphenidate and Atomoxetine in Children with Attention-Deficit/Hyperactivity Disorder (ADHD): Data from the Italian National ADHD Registry

Abstract

Objective: The aim of this study was to assess the type and frequency of adverse events (AEs) in children with attention-deficit/hyperactivity disorder (ADHD) treated with methylphenidate or atomoxetine over a 5-year period in a large naturalistic study.

Methods: We draw on data from the Italian ADHD Registry, a national database for postmarketing phase IV pharmacovigilance of ADHD medications across 90 centers. AEs were defined as severe or mild as per the classification of the Italian Medicines Agency. AE frequency in the two treatment groups was compared using incidence rates per 100 person-years (IR100PY) and incidence rate ratios (IRRs). Mantel-Haenszel adjusted IRRs were calculated to control for psychiatric comorbidity.

Results: A total of 1350 and 753 participants (aged 6-18 years, mean age 10.7 ± 2.8) were treated with methylphenidate and atomoxetine, respectively, from 2007 to 2012. Ninety participants (7 %) were switched from methylphenidate to atomoxetine, and 138 (18 %) from atomoxetine to methylphenidate. Thirty-seven children treated with atomoxetine and 12 with methylphenidate had their medication withdrawn. Overall, 645 patients (26.8 %) experienced at least one mild AE (including decreased appetite and irritability, for both drugs) and 95 patients (3.9 %) experienced at least one severe AE (including severe gastrointestinal events). IR100PY were significantly higher in the atomoxetine-treated group compared with the methylphenidate-treated group for a number of mild and severe AEs and for any severe or mild AEs. After controlling for comorbidities, IRR was still significantly higher in the atomoxetine group compared with the methylphenidate group for a number of mild (decreased appetite, weight loss, abdominal pain, dyspepsia, stomach ache, irritability, mood disorder and dizziness) and severe (gastrointestinal, neuropsychiatric, and cardiovascular) AEs.

Conclusions: In this naturalistic study, methylphenidate had a better safety profile than atomoxetine.