Pharmacogenomics and metabolite measurement for 6-mercaptopurine therapy in inflammatory bowel disease

Gastroenterology. 2000 Apr;118(4):705-13. doi: 10.1016/s0016-5085(00)70140-5.


Background & aims: The effects of 6-mercaptopurine (6-MP) are mediated via its intracellular conversion to 6-thioguanine (6-TG) and 6-methylmercaptopurine (6-MMP) nucleotide metabolites, the latter genetically controlled by thiopurine methyltransferase (TPMT). We sought to determine optimal therapeutic 6-MP metabolite levels and their correlation with medication-induced toxicity and TPMT genotype.

Methods: Therapeutic response was determined in 92 pediatric patients with inflammatory bowel disease coincidentally with hematologic, pancreatic, and hepatic laboratory parameters, and compared with erythrocyte metabolite levels and TPMT genotype.

Results: Clinical response was highly correlated with 6-TG levels (P < 0.0001) but not with any other variable, including 6-MMP levels, drug dose, gender, and concurrent medications. The frequency of therapeutic response increased at 6-TG levels > 235 pmol/8 x 10(8) erythrocytes (P < 0.001). Hepatotoxicity correlated with elevated 6-MMP levels (>5700 pmol/8 x 10(8) erythrocytes; P < 0.05). Although leukopenia was associated with higher 6-TG levels (P < 0.03), it was observed in only 8% of responders. Patients heterozygous for TPMT (8/92) had higher 6-TG levels (P < 0.0001), and all responded to therapy.

Conclusions: 6-MP metabolite levels and TPMT genotyping may assist clinicians in optimizing therapeutic response to 6-MP and identifying individuals at increased risk for drug-induced toxicity.

Publication types

  • Clinical Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Child
  • Child, Preschool
  • Dose-Response Relationship, Drug
  • Female
  • Genotype
  • Humans
  • Immunosuppressive Agents / therapeutic use*
  • Infant
  • Inflammatory Bowel Diseases / drug therapy*
  • Inflammatory Bowel Diseases / genetics
  • Inflammatory Bowel Diseases / metabolism
  • Leukopenia / chemically induced
  • Liver / metabolism
  • Male
  • Mercaptopurine / adverse effects
  • Mercaptopurine / analogs & derivatives
  • Mercaptopurine / metabolism
  • Mercaptopurine / therapeutic use*
  • Mesalamine / therapeutic use
  • Methyltransferases / genetics
  • Prospective Studies
  • Thioguanine / blood
  • Treatment Outcome


  • Immunosuppressive Agents
  • methyl-6-mercatopurine
  • Mesalamine
  • Mercaptopurine
  • Methyltransferases
  • thiopurine methyltransferase
  • Thioguanine