Determination of fenoldopam (SK&F 82526) and its metabolites in human plasma and urine by high-performance liquid chromatography with electrochemical detection.

Fenoldopam [6-chloro-2,3,4,5-tetrahydro-1-(4-hydroxyphenyl)-1H-3-benzazepine-7,8-di ol] is a potent renal vasodilator that is currently undergoing Phase II clinical trials. Quantitative analytical methods, based on high-performance liquid chromatography with electrochemical detection (HPLC-ED) after ethyl acetate extraction from plasma or urine were developed for the determination of fenoldopam and its identified metabolites in biological media. The lower limit of quantitation for fenoldopam in plasma was 50 pg/ml. In assays for fenoldopam glucuronide(s) and fenoldopam conjugates, urine was treated with beta-glucuronidase and Glusulase, respectively, and the liberated fenoldopam was quantified by HPLC-ED. A novel assay by dual-electrode (in series) HPLC-ED was developed for the 8-sulfate of fenoldopam. In this method, the 8-sulfate was oxidized to the o-quinone at the first electrode and quantitated at the second electrode after reduction to the catechol. A similar dual-electrode HPLC-ED method was used for 7- and 8-O-methyl fenoldopam. Conjugates of the O-methyl metabolites were determined by HPLC-ED after hydrolysis to O-methyl fenoldopam. These methods have been used to study the kinetics and metabolism of fenoldopam in healthy volunteers. The methods are specific, sensitive, reproducible, and linear over a wide range of concentrations. Precision of the analyses, expressed as coefficients of variation, were less than 10% for all analyses.