DETERMINATION OF LINOPIRDINE AND ITS MONO-N-OXIDE METABOLITE IN HUMANPLASMA AND URINE BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

Sensitive and selective high-performance liquid chromatographic method s for the determination of linopirdine, a novel cognitive enhancer, an d a major metabolite, linopirdine mono-N-oxide, in human plasma and ur ine are described. For plasma, alkalyzed samples were extracted with e thyl acetate. For urine, neutral samples were extracted with ethyl ace tate and further treated by solid-phase extraction. The plasma residue s were chromatographed on a Beckman CN HPLC column and the urine resid ues on a Jones Apex II CN HPLC column (both 4.6 x 25 cm). The mobile p hase consisted of acetonitrile-ammonium acetate mixed with glacial ace tic acid, 1-octane sulfonic acid and triethlyamine. The flow rate was 1.5 ml/min and the compounds were detected by UV at 254 nm. The lower limits of quantification for linopirdine and linopirdine mono-N-oxide were 2.5 ng/ml in plasma and 10.0 ng/ml and 100 ng/ml, respectively, i n urine. The precision and accuracy, expressed as the percent coeffici ent of variation and percent difference, respectively, were <20 percen t for the assays. The methods were used to study the pharmacokinetics of linopirdine and linopirdine mono-N-oxide in human subjects.