A radioimmunoassay to measure piretanide in human serum and urine.

This paper describes a specific radioimmunological method for determining the diuretic agent piretanide (4 phenoxy-3-(1-pyrrolidinyl)-5-sulfamoyl benzoic acid) in human serum, plasma and urine. The antiserum was raised in rabbits against an immunogen of piretanide coupled to bovine serum albumin. The iodinated hydroxy derivative of piretanide was used as tracer. The separation of free and antibody-bound piretanide was performed by precipitating the antibody-tracer complex by polyethylene glycol. The limit of detection was 4 ng/ml. Studies on specificity showed less than 0.5% cross-reactivity of an identified metabolite. Interassay reproducibility showed an average coefficient of variation of 7.3%, the interassay variation was 5%. A recovery experiment yielded 100.9% recovery. There is good agreement between parallel determinations of piretanide by RIA and HPLC in both human serum and urine.