Determination and pharmacokinetics of a furosemide-amiloride drug combination

The study presents an accurate and precise HPLC assay for the determination of furosemide and amiloride in human specimens. Both drugs were extracted from human plasma with ethyl acetate; furosemide was extracted at pH 1 and amiloride at pH 12. While chromatographic separation conditions, i.e., column, mobile phase and flow-rate were the same for both investigated drugs, furosemide was detected using a UV absorbance detector, whereas amiloride, because of its very low therapeutic range, was detected with a spectrofluorimetric detector. The linearity of the furosemide and amiloride assays were confirmed over the range of 30-3000 ng/ml and 0.5-30 ng/ml, respectively. These concentrations correspond well with the therapeutic ranges of both drugs. The extraction recoveries, depending on concentration, exceed 80% for furosemide and 74% for amiloride. The reported methods were applied to pharmacokinetic investigations of the two compounds taken in form of a drug combination.