Correlations between motor persistence and plasma levels in methylphenidate-treated boys with ADHD

Following a 0.9 mg/kg methylphenidate loading dose, serial plasma level det erminations, self-scored mood ratings, and measures of motor persistence we re gathered on eight previously unmedicated boys with attention deficit dis order with hyperactivity (ADHD) during a 9-h period. The measures were repe ated using the same loading dose after 6 months of maintenance treatment wi th methylphenidate (1.3 mg/kg.d). Kinetic-dynamic modelling suggests invers e correlative relationships between motor performance errors and plasma lev els. Pharmacokinetic parameters did not change between acute and maintenanc e drug treatment phases, and there was no evidence of long-term tolerance.