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Objective: The aim of this study was to examine immediate-release methylphenidate effectiveness during the 10-month open-label continuation phase of the Preschoolers with attention-deficit/hyperactivity disorder (ADHD) Treatment Study (PATS).

Methods: One hundred and forty preschoolers with ADHD, who had improved with acute immediate-release methylphenidate (IR-MPH) treatment, entered a 10-month, open-label medication maintenance at six sites. Assessments included the Clinical Global Impression-Severity (CGI-S), CGI-Improvement (CGI-I), Children's Global Assessment Scale (C-GAS), Swanson, Nolan, and Pelham Questionnaire (SNAP), Scale Strengths and Weaknesses of ADHD-Symptoms and Normal Behaviors (SWAN), Social Competence Scale, Social Skills Rating System (SSRS), and Parenting Stress Index–Short Form (PSI-SF).

Results: For the 95 children who completed the 10-month treatment, improvement occurred on the CGI-S (p = 0.02), CGI-I (p < 0.01), C-GAS (p = 0.001), and SSRS (p = 0.01). SNAP and SWAN scores remained stable. Forty five children discontinued: 7 for adverse effects, 7 for behavior worsening, 7 for switching to long-acting stimulants, 3 for inadequate benefit, and 21 for other reasons. The mean MPH dose increased from 14.04 mg/day ± SD 7.57 (0.71 ± 0.38 mg/kg per day) at month 1 to 19.98 mg/day ± 9.56 (0.92 ± 0.40 mg/kg per day) at month 10.

Conclusions: With careful monitoring and gradual medication dose increase, most preschoolers with ADHD maintained improvement during long-term IR-MPH treatment. There was substantial variability in effective and tolerated dosing.