Rapid assay for the quantification of piretanide in biological fluids

Piretanide was determined from plasma and urine using reversed-phase high-performance liquid chromatography. Plasma was extracted with diethylether at pH 4 using bumetanide as internal standard. The chromatographic separation was performed on an octadecylsilane column (ODS) with acetonitrile/pH 7 phosphate buffer (3:7, v/v). In order to determine piretanide in urine, bumetanide was added to a urine aliquot. Then the sample was centrifuged and the supernatant directly injected without extraction followed by chromatography on an ODS column with a mixture of methanol and pH 7 phosphate buffer (12:13, v/v). The compounds were detected by their intrinsic fluorescence, monitoring the eluate at 287/450 nm. Total chromatography times were 8 min for plasma and 13 min for urine samples. The method was applied for the assay of piretanide in plasma of healthy volunteers after i.v. or p.o. dosage of 6 mg piretanide.