Phenotyping for Thiopurine Therapy in Clinical Practice

Aim To quantify the uptake of thiopurine methyltransferase (TPMT) phenotyping in patients on thiopurines. Method A retrospective audit was undertaken to identify all patients initiated on thiopurines from 1 August 2003 to 31 May 2006 at a tertiary referral hospital. All patients dispensed azathioprine, mercaptopurine and thioguanine were identified from computerised dispensing records. TPMT phenotype test results were obtained from the hospital's pathology service for the period 1 July 2003 to 30 June 2006. Results Of the 287 patients initiated on thiopurines, 21 (8.8%) had TPMT activity measured. Thiopurines were widely prescribed across a number of medical disciplines with the largest usage in the transplant units − 88 lung transplant recipients and 3 dual heart and lung transplant recipients. Only one transplant recipient had TPMT activity measured. In the dermatology unit, 47% of patients receiving thiopurines underwent TPMT phenotyping. Conclusion The uptake of TPMT phenotyping in patients on thiopurines was low and variable depending on the clinical unit. Further efforts to increase the uptake of TPMT phenotyping before initiation of thiopurine therapy are warranted.