The primary objective of this study was to evaluate the efficacy of atomoxetine (ATX, target dose 1.2 mg/kg daily) on symptoms of oppositional defiant disorder (ODD) in children and adolescents with attention-deficit/hyperactivity disorder (ADHD). A secondary objective was to compare fast versus slow up-titration of ATX.
This was a 3-arm, 9-week, randomized, placebo-controlled, double-blind study in ADHD patients (6-17 years) with comorbid ODD (Diagnostic and Statistical Manual of Mental Disorders, 4th edition [DSM-IV] criteria A-C) or conduct disorder (CD). ATX-treatment arms were as follows-ATX-fast: 7 days 0.5 mg/kg, then 1.2 mg/kg; ATX-slow: 7 days each at 0.5 and 0.8 mg/kg, then 1.2 mg/kg. Primary outcome was the Swanson, Nolan, and Pelham Rating Scale-Revised (SNAP-IV) ODD-score after 9 weeks (Mixed Effects Model for Repeated Measures, ATX-up-titration groups pooled).
In total, 181 patients were randomized, and 180 evaluated (ATX-fast/ATX-slow/placebo: 60/61/59). Baseline characteristics were comparable (84.4% boys; mean age 11.0 years; DSM-IV: 100% ADHD, 75.6% with combined type, 74.4% ODD, 24.4% CD; SNAP-IV ODD-scores, mean ± standard deviation 15.5 ± 4.35). At week 9, SNAP-IV ODD scores were significantly lower versus placebo in both ATX-groups (least square mean [95% confidence interval]: ATX-fast 8.6 [7.2;9.9]; ATX-slow 9.0 [7.7;10.3]; placebo 12.0 [10.6;13.5]; least square mean, ATX-pooled minus placebo: -3.2 [-5.0, -1.5], effect size: -0.69, p < 0.001). SNAP-IV ADHD-scores, CD symptoms (investigator-rated Attention-Deficit and Disruptive Behavior Disorders Instrument, disruptive behavior), Clinical Global Impressions-Severity, and individual treatment behaviors showed corresponding results. Post-hoc analyses indicated interrelationships between the medication effects on ADHD, ODD, and CD symptom scores. For ATX-slow, time to early dropout was significantly longer versus placebo (Hazard Ratio [95% confidence interval]: 3.57 [1.42;8.94]; p = 0.007). Clinically relevant adverse effects (fatigue, sleep disorders, nausea, and gastrointestinal complaints; weeks 1-3) were reported in 60.0% of ATX-fast, 44.3% of ATX-slow, and 18.6% of placebo group patients.
ATX for 9 weeks significantly reduced symptoms of ODD/CD and ADHD; slower ATX-up-titration may be better tolerated.