A Rapid and Robust HPLC- DAD Method for the Monitoring of Thiopurine Metabolites in Whole Blood: Application to Paediatric Patients with Inflammatory Bowel Disease

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.