Expedient liquid chromatographic analysis of azathioprine in plasma by use of silica solid phase extraction.

We report an expedient analysis of azathioprine (AZN) in plasma by use of a radial compression liquid chromatography and silica solid phase extraction. The separation of the drug and internal standard (antipyrine) was achieved on a C18 cartridge using a mixture of 0.01 M aqueous solution of sodium phosphate (pH = 4.5) and methanol (87:13; vol/vol) as the mobile phase. The assay is highly specific with no interference from any endogenous substance or concomitantly used drug. The peak height ratio of drug to internal standard was linearly (r greater than 0.09976) related to concentration in the range 0.005-2 micrograms/ml, and the within-run and between-day coefficient of variation did not exceed 6.9% at any concentration. This study measured the steady-state concentration of azathioprine in plasma of renal transplants patients. Also, the applicability of this method to study the pharmacokinetics of AZN following a single intravenous administration was examined, using the rabbit as an in vivo model.