COMPARISON OF 2 HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC METHODS FOR MONITORING PLASMA-CONCENTRATIONS OF HALOPERIDOL AND REDUCED HALOPERIDOL

Two high-performance liquid chromatographic methods for monitoring hal operidol (HAL) and reduced haloperidol (RHAL) plasma concentrations we re compared. In one method ultraviolet detection and a C18 column were used (UV method); in the other method electrochemical detection and a CN-coluInn were used (EC method). Both methods are accurate and preci se. For plasma samples spiked with HAL or RHAL, an excellent correlati on was observed between the concentrations of HAL and RHAL found with both methods (r less than or equal to 0.99, p < 0.01). However, for pl asma obtained from patients treated with HAL the correlation between t he two methods was poor (r greater than or equal to 0.71, p < 0.01). T he main reason for the discrepancy between the two methods is probably interference of comedications or their metabolites, mostly in the EC method. Although the quantitation limit of the UV method (3 ng/ml for HAL and RHAL) is higher than that of the EC method (0.5 ng/ml for HAL and RHAL), the UV method is to be preferred for monitoring plasma leve ls in psychiatric patients because there is less interference from com edication.