HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC DETERMINATION OF THE N-ETHYL TRICARBAMATE ESTER PRO-DRUG OF FENOLDOPAM UTILIZING SIMULTANEOUS POSTCOLUMN 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 est er pro-drug of fenoldopam, in dog plasma. Fenoldopam is a selective ag onist of peripheral dopaminergic (DA-1) receptors and has been shown t o improve blood flow and lower blood pressure. The method involves iso lation of I and the internal standard (I.S.) from plasma by solid-phas e extraction prior to chromatographic separation on an octyl silica co lumn. 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 solut ion of o-phthaldialdehyde and a thiol, to generate a highly fluorescen t 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%, respecti vely. The limit of quantification for I using 0.2 mi of plasma was 5 n g/ml. Linear response was observed for concentrations of I ranging fro m 5 to 2000 ng/ml plasma. The method was suitably specific and sensiti ve for pharmacokinetic and metabolic studies of I in dogs. The methodo logy developed should be generally applicable to the determination of carbamate-type pro-drugs in biological media.