Capillary electrophoresis determination of thiopurine methyl transferase activity in erythrocytes

Thiopurine S-methyltransferase (TPMT) catalyzes methylation of thiopurine drugs (e.g. 6-mercaptopurine, azathioprine). Decreased activity of TPMT is associated with hematopoietic toxicity after administration of standard doses of the drugs. We developed capillary electrophoretic method for determination of TPMT enzyme activity in erythrocytes. Limit of quantification of the method is 1.5 micromol/L (S/N=6). The recovery of 6-methylmercaptopurine was 87.5-94.8%, imprecision value (as CV, n=10) was 1.68% (within-day) and 2.53% (between-day). Erythrocyte TPMT activities were measured in 60 healthy adult volunteers.