HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC PROCEDURE FOR THE DETERMINATION OF TIAGABINE CONCENTRATIONS IN HUMAN PLASMA USING ELECTROCHEMICAL DETECTION

A sensitive and precise high-performance liquid chromatographic procedure has been developed for the measurement of tiagabine concentrations in human plasma. Isolation of tiagabine and the internal standard was achieved using solid-phase extraction on disposable C-8 columns. Separation was performed on a C18 analytical column using a mobile phase containing sodium octanesulfonate. The effluent was monitored with coulometric electrochemical detection at ca. + 0.76 V. The workup procedure recovered more than 95% of tiagabine from plasma. Standard curves were linear over the concentration range 0-500 ng/ml. The precision of the method was good: coefficients of variation were typically less than 5% for concentrations as low as 8 ng/ml and although they were higher at concentrations less than 8 ng/ml, they remained within acceptable limits (less than 17%) for concentrations as low as the limit of quantitation (2 ng/ml using a 1-ml plasma sample). The stability of tiagabine in plasma was excellent, with no evidence of degradation after 23 h at room temperature or 2 months at -20-degrees-C.