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Aims: To determine factors for switching to osmotic release oral system methylphenidate (OROS-MPH) among poor adherents to immediate-release methylphenidate (IR-MPH); and to compare the efficacy of OROS-MPH on the three attention-deficit/hyperactivity disorder (ADHD) subtypes in a multi-site prospective observational study in Taiwan.
Methods: The sample included 240 children with ADHD, aged 6–16 years, who were poor adherents to IR-MPH, 137 of whom were switched to OROS-MPH. The child psychiatrists diagnosed the Diagnostic Statistical Manual of Mental Disorders (4th edition) ADHD subtypes and assessed the medical history, adherence, side-effects, global ADHD severity, and family/school effectiveness. Parents reported their child's behavioral symptoms.
Results: The determinants for an OROS-MPH switch were higher dosage, shorter treatment and thrice-daily administration of IR-MPH, and more severe inattention symptoms. Hyperactivity and oppositional symptoms were greater in the ADHD combined and hyperactive-impulsive subtypes than the inattentive subtype. Switching to OROS-MPH significantly improved behavioral symptoms and family/school measures, and this was most evident in the ADHD-combined group, followed by the ADHD-inattentive group. Inattention influenced not only academic performance, but also overall classroom behaviors and the parent–child relationship, with the latter two also influenced by oppositional symptoms.
Conclusions: This study suggests better efficacy for the OROS-MPH among poor adherents to IR-MPH; however, its effectiveness varied across the three ADHD subtypes (ClinicalTrials.gov number NCT00460720).
ATTENTION-DEFICIT/HYPERACTIVITY DISORDER (ADHD), a common childhood disorder with worldwide-pooled prevalence estimated at 5.29%,1 affects 7.5% of the school-aged children in Taiwan.2 Given the impact of ADHD on individuals, families and society, affected individuals usually need treatment3–5 and the published reports have clearly documented pharmacotherapy as an effective, fundamental and superior treatment strategy compared to psychosocial interventions alone regarding ADHD symptom reduction.6
Methylphenidate (MPH) is the most commonly used and extensively studied medication for ADHD,4 and its immediate-release (IR) formulation (IR-MPH) was the only stimulant medication used for ADHD in Taiwan until the osmotic release oral system (OROS) was launched in October 2003.5 Because IR-MPH has a relatively short half-life, maintenance of therapeutic efficacy typically necessitates administration two or three times a day,7 with this staggered dosing causing adherence problems,7 which, in turn, leads to suboptimal symptom management of ADHD and less-than-favorable outcomes in terms of psychosocial and academic functioning.6
Although Western studies7 and our previous studies5,8,9 have identified several predictors for poor adherence to IR-MPH such as multiple daily dosing,5,7 older age,5 and intolerable side-effects,5,7 little is known about determinants for OROS-MPH adherence.
A few investigations comparing MPH efficacy across three ADHD subtypes have reported that the efficacy of OROS-MPH treatment is particularly evident for the predominantly inattentive ADHD subtype (ADHD-I),10 and that MPH comparably reduced inattention in both ADHD-I and the combined subtype (ADHD-C), whereas reduction in hyperactivity was more evident in ADHD-C.11 However, Barbaresi et al.12 did not find different responses to MPH among the ADHD subtypes.
Therefore, this study aimed to: (i) identify potential predictors for the switch to OROS-MPH in poor IR-MPH adherents; (ii) determine the predictors for OROS-MPH adherence; and (iii) compare the changes in behavioral symptoms, parent–child interaction, classroom behavior, and academic performance among children with one of three ADHD subtypes.