Is It Useful to Test Thiopurine Methyltransferase Activity Before Initiating Azathioprine?

Researchers did not find a link between abnormal TPMT activity and toxicity, but testing is easy.

Azathioprine sodium is used as adjuvant treatment of pemphigus vulgaris. Azathioprine and 6-mercaptopurine are metabolized by thiopurine methyltransferase (TPMT). Because of concerns about toxicity in patients with very low levels of TPMT activity, testing such activity before initiating azathioprine therapy has become standard care in the U.S.

Investigators in Iran reviewed the relation between TPMT activity and risk for toxicity in 139 patients with pemphigus. They found 11 patients with low activity (7.9%) and 1 patient with supranormal levels. Patients received standard dosing with 2 mg/kg/day of prednisone and 2 to 3 mg/kg/day of azathioprine. Fourteen patients discontinued azathioprine because of adverse effects, including 11 due to ab…

Reviewing Author

Jeffrey P. Callen, MD

Disclosures

Consultant / Advisory board XOMA; Eli Lilly; Celgene

Equity Various trust accounts

Editorial boards JAMA Dermatology; UpToDate

Leadership positions in professional societies Association of Professors of Dermatology (President-Elect)

Jeffrey P. Callen, MD

Disclosures

Consultant / Advisory board XOMA; Eli Lilly; Celgene

Equity Various trust accounts

Editorial boards JAMA Dermatology; UpToDate

Leadership positions in professional societies Association of Professors of Dermatology (President-Elect)