Mercaptopurine (MP) and azathioprine (AZA) are thiopurine drugs that are used in paediatrics
for the treatment of inflammatory bowel disease (IBD), Therapeutic drug monitoring (TDM) of thiopurine
active metabolites, 6-methylmercaptopurine (6MMP) and 6-thioguanine nucleotides (6-TGN) is a
common practice for the assessment of toxicity surveillance and treatment optimization. In this paper we
described the development and validation of a new High Performance Liquid Chromatography coupled to Diode Array
Detection (HPLC-DAD) method for the simultaneous quantification of 6-TGN and 6-MMP in whole blood with a total
runtime of 7.5 minutes over a wide range of concentrations (50 – 2000 pmol/8x10^8 RBC for 6-TG and 20 – 15000
pmol/8x10^8 RBC for 6-MMP respectively). The new method has been validated following international guidelines on
bioanalytical method validation. Within- and between-run precision and accuracy results for quality control samples were
always ≤ 15% of the nominal concentrations. The correlation with our reference method was excellent. The new HPLCDAD
method that we describe is robust, rapid, cost effective and suitable for application to the routine TDM analyses.
Keywords: HPLC, thiopurines, metabolites, azathioprine, therapeutic drug monitoring.
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