This has been confirmed in human trials, where thioguanine has proven to be safe but efficacious for coeliac disease when used at doses below those commonly prescribed. This has led to a revival of interest in thioguanine because of its higher efficacy and faster action compared to other thiopurines and immunosuppressants such as mycophenylate. Contraindications
Pregnancy
Lactation: The safety warning against breastfeeding may have been a conservative assessment, but research evidence suggests that thiopurines do not enter breastmilk. Interactions
Cancers that do not respond to treatment with mercaptopurine do not respond to thioguanine. On the other hand, some cases of IBD that are resistant to mercaptopurine (or its pro-drug azathioprine) may be responsive to thioguanine. Pharmacogenetics
The enzyme thiopurine S-methyltransferase (TPMT) is responsible for the direct inactivation of thioguanine to its methylthioguanine base – this methylation prevents thioguanine from further conversion into active, cytotoxic thioguanine nucleotide (TGN) metabolites. Certain genetic variations within the TPMT gene can lead to decreased or absent TPMT enzyme activity, and individuals who are homozygous or heterozygous for these types of genetic variations may have increased levels of TGN metabolites and an increased risk of severe bone marrow suppression (myelosuppression) when receiving thioguanine. In many ethnicities, TPMT polymorphisms that result in decreased or absent TPMT activity occur with a frequency of approximately 5%, meaning that about 0.25% of patients are homozygous for these variants.
6-TGN are cytotoxic to cells by: (1) incorporation into DNA during the synthesis phase (S-phase) of the cell; and (2) through inhibition of the GTP-binding protein (G protein) Rac1, which regulates the Rac/Vav pathway. Chemistry
It is a pale yellow, odorless, crystalline powder. Names
Tioguanine (INN, BAN, AAN), or thioguanine (USAN). Thioguanine is administered by mouth (as a tablet – Lanvis). References
Further reading
Dean L (2012). "Thioguanine Therapy and TPMT Genotype". In Pratt VM, McLeod HL, Rubinstein WS,  et al. (eds.). Medical Genetics Summaries. National Center for Biotechnology Information (NCBI). PMID 28520351. Bookshelf ID: NBK100663. External links
"Tioguanine". Drug Information Portal. U.S. National Library of Medicine.