High-performance liquid chromatographic determination of the N-ethyl tricarbamate ester pro-drug of fenoldopam utilizing simultaneous post-column hydrolysis and fluorescence derivatization

A high-performance liquid chromatographic (HPLC) method was developed for the determination of SK&F 105058 (I), the N-ethyl tricarbamate ester pro-drug of fenoldopam, in dog plasma. Fenoldopam is a selective agonist of peripheral dopaminergic (DA-1) receptors and has been shown to improve blood flow and lower blood pressure. The method involves isolation of I and the internal standard (I.S.) from plasma by solid-phase extraction prior to chromatographic separation on an octyl silica column. Following chromatographic separation, the carbamate esters of I and I.S. were simultaneously hydrolyzed and the liberated alkylamines were derivatized, by mixing the column effluent with an alkaline solution of o -phthaldialdehyde and a thiol, to generate a highly fluorescent isoindole product which was subsequently detected with a fluorometer. Optimization of chromatographic and post-column reaction conditions resulted in an on-column detection limit of 0.4 ng. The recoveries for I and I.S. from plasma were 80.0 ± 5.0% and 62.0 ± 4.0%, respectively. The limit of quantification for I using 0.2 ml of plasma was 5 ng/ml. Linear response was observed for concentrations of I ranging from 5 to 2000 ng/ml plasma. The method was suitably specific and sensitive for pharmacokinetic and metabolic studies of I in dogs. The methodology developed should be generally applicable to the determination of carbamate-type pro-drugs in biological media.