SIMULTANEOUS DETERMINATION OF ACETYLSALICYLIC-ACID AND SALICYLIC-ACIDIN HUMAN PLASMA BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

A high-performance liquid chromatographic (HPLC) method is described f or the simultaneous determination of acetylsalicylic acid (ASA) and it s main metabolite salicylic acid (SA) in human plasma. Acidified plasm a is deproteinized with acetonitrile which is separated from the aqueo us layer by adding sodium chloride. ASA and SA are extracted into the acetonitrile layer with high yield, and determined by reversed-phase H PLC (column: Novapak C-18 4 mu m silica, 150X4 mm I.D.; eluent: 740 ml water, 900 mu l 85% orthophosphoric acid, 180 ml acetonitrile) and ph otometric detection (237 nm). 2-Methylbenzoic acid is used as internal standard. The method allows the determination of ASA and SA in human plasma as low as 100 ng/ml with good precision (better than 10%). The assay was used to determine the pharmacokinetic parameters of ASA and SA following oral administration of 100-500 mg ASA in healthy voluntee rs.