Comparison of extraction and precipitation methods for the HPLC determination of furosemide in plasma and urine

Abstract

Comparisons have been made between an ether extraction method and an acetonitrile precipitation method for the HPLC determination of furosemide (frusemide) in human plasma and urine. Recoveries of furosemide were 81-89% (ether extraction method for plasma), 73-103% (acetonitrile precipitation method for plasma) and 62-89% (ether extraction method for urine) for the concentration ranges studied. Values of correlation coefficients were 0.9998, 0.9991 and 0.9997 for standard curves for the three methods, respectively. Accuracy and precision (RSD) were: 92.4-114% +/- 3.57-20% for ether-extracted plasma; 98.1-103% +/- 3.47-19.9% for acetonitrile-precipitated plasma; and 103-107% +/- 4.03-13.2% for ether-extracted urine. Because of carryover of endogenous urine components, the acetonitrile-precipitation assay was unacceptable for urine. Furosemide was stable in frozen plasma for at least 113 days and in frozen urine for at least 204 days. No artifactual appearance of the hydrolysis product of furosemide, 4-chloro-5-sulfamoylanthranilic acid (CSA), was detected by the ether-extraction method under normal assay conditions.