Efficacy and Safety of Lisdexamfetamine Dimesylate and Atomoxetine in the Treatment of Attention-Deficit/Hyperactivity Disorder: a Head-to-Head, Randomized, Double-Blind, Phase IIIb Study

OBJECTIVES The aim of this study was to compare the efficacy and safety of the prodrug psychostimulant lisdexamfetamine dimesylate (LDX) and the non-stimulant noradrenergic compound atomoxetine (ATX) in children and adolescents with attention-deficit/hyperactivity disorder (ADHD) who had previously responded inadequately to methylphenidate (MPH). METHODS This 9-week, head-to-head, randomized, double-blind, active-controlled study (SPD489-317; ClinicalTrials.gov NCT01106430) enrolled patients (aged 6-17 years) with at least moderately symptomatic ADHD and an inadequate response to previous MPH therapy. Patients were randomized (1:1) to an optimized daily dose of LDX (30, 50 or 70 mg) or ATX (patients <70 kg, 0.5-1.2 mg/kg with total daily dose not to exceed 1.4 mg/kg; patients ≥70 kg, 40, 80 or 100 mg). The primary efficacy outcome was time (days) to first clinical response. Clinical response was defined as a Clinical Global Impressions-Improvement (CGI-I) score of 1 (very much improved) or 2 (much improved). Secondary efficacy outcomes included the proportion of responders at each study visit and the change from baseline in ADHD Rating Scale (ADHD-RS-IV) and CGI-Severity scores. Tolerability and safety were assessed by monitoring treatment-emergent adverse events (TEAEs), height and weight, vital signs and electrocardiogram parameters. Endpoint was defined as the last post-baseline, on-treatment visit with a valid assessment. RESULTS Of 267 patients randomized (LDX, n = 133; ATX, n = 134), 200 (74.9%) completed the study. The median time to first clinical response [95% confidence interval (CI)] was significantly shorter for patients receiving LDX [12.0 days (8.0-16.0)] than for those receiving ATX [21.0 days (15.0-23.0)] (p = 0.001). By week 9, 81.7% (95% CI 75.0-88.5) of patients receiving LDX had responded to treatment compared with 63.6% (95% CI 55.4-71.8) of those receiving ATX (p = 0.001). Also by week 9, the difference between LDX and ATX in least-squares mean change from baseline (95% CI) was significant in favour of LDX for the ADHD-RS-IV total score [-6.5 (-9.3 to -3.6); p < 0.001; effect size 0.56], inattentiveness subscale score [-3.4 (-4.9 to -1.8); p < 0.001; effect size 0.53] and the hyperactivity/impulsivity subscale score [-3.2 (-4.6 to -1.7); p < 0.001; effect size 0.53]. TEAEs were reported by 71.9 and 70.9% of patients receiving LDX and ATX, respectively. At endpoint, both treatments were associated with mean (standard deviation) increases in systolic blood pressure [LDX, +0.7 mmHg (9.08); ATX, +0.6 mmHg (7.96)], diastolic blood pressure [LDX, +0.1 mmHg (8.33); ATX, +1.3 mmHg (8.24)] and pulse rate [LDX, +3.6 bpm (10.49); ATX, +3.7 bpm (10.75)], and decreases in weight [LDX, -1.30 kg (1.806); ATX, -0.15 kg (1.434)]. CONCLUSIONS LDX was associated with a faster and more robust treatment response than ATX in children and adolescents with at least moderately symptomatic ADHD who had previously responded inadequately to MPH. Both treatments displayed safety profiles consistent with findings from previous clinical trials.