Determination of aditoprim, a new dihydrofolate reductase inhibitor, in the plasma of cows and pigs

Abstract

A selective and sensitive high-performance liquid chromatographic method was developed for the determination of aditoprim, a new dihydrofolate reductase inhibitor, in the plasma of cows and pigs. The compound and its internal standard were extracted with chloroform from plasma buffered at pH 9 and chromatographed on a muBondapak reversed-phase column with a mixture of acetonitrile and 0.5% ammonium carbonate aqueous solution and detected by UV absorption. Aditoprim can be quantitatively extracted from plasma. The limit for quantitative determination was ca. 0.050 micrograms/ml with a standard deviation of +/- 0.006 micrograms/ml and an accuracy of +/- 3%. The assay was linear over the concentration range 0.1-5.0 micrograms/ml (precision 0.007-0.09 micrograms/ml), and the day-to-day accuracy was better than +/- 3.5%. No interference was observed from either metabolite(s) or coadministered sulphonamides. The new procedure was compared with a microbiological assay by analysing plasma samples from pigs treated with aditoprim. The two methods gave similar results in the range 0.5-5.0 micrograms/ml.