Assay of 6-thioguanine nucleotide, a major metabolite of azathioprine, 6-mercaptopurine and 6-thioguanine, in human red blood cells

J Pharm Pharmacol. 1983 Jan;35(1):15-8. doi: 10.1111/j.2042-7158.1983.tb04255.x.


An assay for 6-thioguanine (6-TG) nucleotide, a major metabolite of the cytotoxic drugs azathioprine, 6-mercaptopurine and 6-thioguanine in human red blood cells (RBCs) has been developed. The metabolite was not detected in RBCs when azathioprine or 6-mercaptopurine was incubated with whole blood in-vitro. The assay for intracellular 6-TG nucleotide is specific and requires 8 X 10(8) RBCs (100 microliters packed cells) for which the limit of sensitivity is 30 pmole 6-TG nucleotide. Pre-dose blood samples were obtained, 12 h after the last azathioprine dose, from 10 renal transplant recipients with stable functioning cadaver grafts on a total daily dose of 150 mg azathioprine. The mean 6-TG nucleotide concentration was 171 pmole/8 X 10(8) RBCs (s.d. = 84). The assay is also suitable for use in measuring 6-TG nucleotide in the RBCs of leukaemic children undergoing 6-mercaptopurine treatment.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Azathioprine / metabolism*
  • Erythrocytes / metabolism*
  • Guanine Nucleotides / blood*
  • Humans
  • In Vitro Techniques
  • Leukemia, Lymphoid / blood
  • Mercaptopurine / metabolism*
  • Mercaptopurine / therapeutic use
  • Thioguanine / metabolism*
  • Thionucleotides / blood*


  • Guanine Nucleotides
  • Thionucleotides
  • 6-thioguanylic acid
  • Mercaptopurine
  • Thioguanine
  • Azathioprine