Understanding the State of Pharmacogenomic Testing for Thiopurine Methyltransferase Within a Large Health System

Abstract

Aim: To investigate the current state of TPMT testing at a single-academic medical center. Methods: Single-center, retrospective chart review for patients newly prescribed a thiopurine. Data collection and evaluation included the prevalence and timing of TPMT testing, correct dosage adjustment if applicable, and incidence of myelosuppression. Results: 121 patients (71%) received TPMT testing. Out of the tested patients, 110 (90.9%) were designated as wild-type with normal metabolism. Dosing modification was appropriate in applicable patients. In unadjusted analysis, there was a lower incidence of myelosuppression among patients who were tested versus those who were not (16.5 vs 36.7%). Conclusion: Based on the study results, TPMT testing opportunities exist for nearly 30% of patients. Testing may reduce the incidence of myelosuppression.

Genophenotypic Factors and Pharmacogenomics in Adverse Drug Reactions

“…In cases with deficient or intermediate activity, phenotype sensitivity and specificity are 91.3% and 92.6%, respectively, and for TPMT*2 and TPMT*3 88.9% and 99.2%, respectively [145]. TPMT testing shows that approximately 90% of patients receiving thiopurines are wild-type and that nearly 30% of patients may benefit with TPMT testing and consequent dosing modification to reduce the incidence of myelosuppression [146]. Approximately 0.1% of patients are carriers of novel TPMT alleles (TPMT*42, *43, and *44) recently identified in Sweden [147].…”