IMPROVED HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC DETERMINATION OF AMOXICILLIN IN HUMAN PLASMA BY MEANS OF COLUMN-SWITCHING

A highly sensitive and selective HPLC method was developed for the det ermination of amoxicillin in human plasma. After addition of buffer an d internal standard, the sample was ultrafiltered and injected on to a precolumn to remove polar plasma interferences. Detection was effecte d with a UV detector set at 230 nm. The limit of quantification for am oxicillin was 50.1 ng/ml with an imprecision of 4.2% using 0.25 ml of plasma. Linearity was confirmed over the whole calibration range (25.4 -0.0501 mu g/ml) and the inter-day variation ranged from 2.0 to 4.5%. The method was validated according to GLP guidelines and its suitabili ty was demonstrated by the analysis of several hundred samples in a bi oequivalence study. The method can be used to determine pharmacokineti c parameters of amoxicillin in humans after a single oral dose of 500 mg.