High-performance liquid chromatography-mass spectrometric analysis of furosemide in plasma and its use in pharmacokinetic studies.

This study presents a rapid, specific and sensitive high-performance liquid chromatography-mass spectrometric (LC-MS) assay for the determination of furosemide in human plasma using diclofenac as an internal standard (IS). Both compounds were extracted from human plasma with ethyl acetate at pH 1 and were chromatographed using Shim-Pack GLC-CN column and a mobile phase consisting of acetonitrile and 20 mM ammonium acetate buffer solution pH 7, 4:1 (v/v) at a flow rate 1 ml min(-1). Furosemide and IS were detected by mass spectrometer operated in the negative single ion monitoring mode using APCI as an ionization process at m/z 329.2 and 294.1, respectively. The assay linearity of furosemide was confirmed over the range 50-2,000 ng ml(-1). Detection limit for furosemide in plasma was 10 ng ml(-1). The selected concentration range corresponds well with the plasma concentrations of furosemide for pharmacokinetic study. Intraday and interday relative standard deviations were 1.3-4.7 and 2.7-11.5%, respectively. The extraction recovery percentages of furosemide and IS from plasma were in the range 89.3-97.1%. The developed LC-MS procedure was applied for the determination of the pharmacokinetic parameters of furosemide after an oral administration of tablet formulation (40 mg) to two healthy male volunteers. The calculated parameters were in good agreement with the reported values.