Thiopurine drugs suppress the immune system and are used to treat patients after organ transplants and in the treatment of a wide range of diseases such as leukaemia, inflammatory bowel disease and skin disorders such as eczema. The most commonly used thiopurine drug is called azathioprine.Approximately 0.3% of the population lack thiopurine s-methyltransferase (TPMT), an enzyme which helps remove thiopurine drugs such as azathioprine from the body. In addition approximately 11% of the population have measurable but reduced levels of TPMT (so called intermediate group). Individuals with no TPMT activitycan become severely ill if treated with normal doses of thiopurine drugs. These patients develop bone marrow suppression with a reduction in blood cells, which causes anaemia, infection and abnormal bleeding. Patients from the intermediate group of TPMT deficiency may in some cases have less marked effects. Such side effects can be avoided if TPMT is measured before starting treatment.See MoreSee Less
