Detection of individuals with low thiopurine methyltransferase (TPMT) activity who are at risk for excessive myelosuppression or severe hematopoietic toxicity when taking thiopurine drugs
Detection of individuals with hyperactive TPMT activity who have therapeutic resistance to thiopurine drugs and may develop hepatotoxicity if treated with these drugs
Individuals who are either homozygous or heterozygous for thiopurine methyltransferase (TPMT) deficiency are at risk of developing life-threatening myelosuppression or severe hematopoietic toxicity when placed on standard doses of azathioprine (AZA, Imuran), 6-mercaptopurine (6-MP, Purinethol), or 6-thioguanine (6-TG, Thioguanine Tabloid).
Individuals who have TPMT hyperactivity cannot achieve therapeutic levels with thiopurine drugs, and they may develop hepatotoxicity due to treatment with thiopurine drugs.
Determining a patient's TPMT status prior to starting therapy with a thiopurine drug is, therefore, important for purposes of calculating the optimal drug dosage.
