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 determinations, self-scored mood ratings, and measures of motor persistence were gathered on eight previously unmedicated boys with attention deficit disorder with hyperactivity (ADHD) during a 9-h period. The measures were repeated using the same loading dose after 6 months of maintenance treatment with methylphenidate (1.3 mg/kg x d). Kinetic-dynamic modelling suggests inverse correlative relationships between motor performance errors and plasma levels. Pharmacokinetic parameters did not change between acute and maintenance drug treatment phases, and there was no evidence of long-term tolerance.