Determination of atomoxetine in human plasma by a high performance liquid chromatographic method with ultraviolet detection using liquid–liquid extraction

A HPLC method with UV detection (210 nm) was developed and validated for the quantification of atomoxetine, a new medication for the treatment of attention deficit/hyperactivity disorder, in human plasma. Following a two-step liquid–liquid extraction with diethyl ether, the analyte and internal standard (maprotiline) were separated using an isocratic mobile phase of acetonitrile/phosphate buffer (39/61, v/v, pH 6.6) on a reverse phase Inertsil C18 column. Linearity was verified over the range of 3.12–200 ng/mL atomoxetine in plasma. The lowest limit of detection is 2.5 ng/mL (S/N = 10). This HPLC method was validated with within- and between-batch precisions of 4.9–14.4% and 4.7–13.1%, respectively. The within- and between-batch biases were −1.9 to 1.4% and 0.1–13.8%, respectively. Commonly used psychotropic drugs and frequently coadministered drugs did not interfere with the drug and internal standard. This method is simple, economical and specific, and has been used successfully in a pharmacokinetic study of atomoxetine.