Thioguanine

Pharmacogenomic Information in the Context of the FDA-Approved Drug Label*

The pharmacogenomic releationship between thioguanine and TPMT is well described. See the TPMT VIP and Thiopurines Pathway for more details. Recent work by the Clinical Pharmacogenomics Implementation Consortium (CPIC) has published guidelines for dosing of thioguanine in individuals with TPMT variants.

The FDA recommends, but does not require, genetic testing prior to initiating or reinitiating treatment with Thioguanine.

Excerpt from the Thioguanine (Tabloid) drug label:
"There are individuals with an inherited deficiency of the enzyme thiopurine methyltransferase (TPMT) who may be unusually sensitive to the myelosuppressive effects of thioguanine and prone to developing rapid bone marrow suppression following the initiation of treatment. Substantial dosage reductions may be required to avoid the development of life-threatening bone marrow suppression in these patients. Prescribers should be aware that some laboratories offer testing for TPMT deficiency. Since bone marrow suppression may be associated with factors other than TPMT deficiency, TPMT testing may not identify all patients at risk for severe toxicity. Therefore, close monitoring of clinical and hematologic parameters is important. Bone marrow suppression could be exacerbated by coadministration with drugs that inhibit TPMT, such as olsalazine, mesalazine, or sulphasalazine."

For the complete drug label text with sections containing pharmacogenetic information highlighted, see the Thioguanine (Tabloid) drug label PDF.