DETERMINATION OF PLASMA AZATHIOPRINE AND 6-MERCAPTOPURINE IN PATIENTS WITH RHEUMATOID-ARTHRITIS TREATED WITH ORAL AZATHIOPRINE

Two specific high-performance liquid chromatography methods for determining plasma concentrations of azathioprine and 6 mercaptopurine after oral administration of azathioprine are presented. It was shown that azathioprine is unstable in the blood samples unless immediately cooled in ice water. The 2-amino analog, guaneran, was used as internal standard for azathioprine, which was extracted from plasma with ethylacetate. A Nucleosil C18 column was used for the separation. The detection limit was 6 nM. For quantification of 6-mercaptopurine, 6-thioguanine was used as internal standard. Plasma was deproteinized with HC10 4 and the sample was purified on mercurial cellulose. A Beckman ODS column was used and the detection limit was 5 nM. Phar-macokinetic data fromtwo patients are presented. Unchanged azathioprine was seen until6 h after an oral dose of 32 mg/m 2. © 1990 Raven Press, Ltd., New York.