Atomoxetine pharmacokinetics in children and adolescents with attention deficit hyperactivity disorder

Atomoxetine is indicated for the treatment of attention deficit hyperactivity disorder in children, adolescents, and adults. This study was conducted, in part, to evaluate the single-dose and steady-state pharmacokinetics of atomoxetine in pediatric patients.

This was an open-label, dose-titration study in pediatric patients with attention deficit hyperactivity disorder. Eligible patients could elect to participate in a single-dose or steady-state discontinuation pharmacokinetic evaluation including serial plasma sample collection over 24 hours. Plasma concentrations of atomoxetine, 4-hydroxyatomoxetine, and N-desmethylatomoxetine were determined using an atmospheric pressure chemical ionization liquid chromatography/mass spectrometry/mass spectrometry assay. Pharmacokinetic parameters were calculated using noncompartmental analysis.

Twenty-one cytochrome P450 2D6 extensive metabolizer patients participated in these single-dose and steady-state pharmacokinetic evaluations. Atomoxetine was rapidly absorbed, with peak plasma concentrations occurring 1 to 2 hours after dosing. Half-life averaged 3.12 and 3.28 hours after a single dose and at steady state, respectively. Minimal accumulation occurred in plasma after multiple twice-daily dosing in extensive metabolizer pediatric patients, as expected based on single-dose pharmacokinetics. As the dose (in mg/kg) increased, proportional increases in area under the curve were observed.

The pharmacokinetics of atomoxetine in extensive metabolizer patients were well characterized over a wide range of doses in this study. Atomoxetine pharmacokinetics in pediatric patients and adult subjects were similar after adjustment for body weight.