Tizoxanide-d4 is intended for use as an internal standard for the quantification of tizoxanide by GC- or LC-MS. Tizoxanide is an active metabolite of the antiparasitic nitazoxanide .1 Tizoxanide is formed from nitazoxanide via deacetylation of nitazoxanide in the stomach. It is active against M. tuberculosis (MIC = 16 μg/ml). It also reduces the growth of the disease-causing parasites L. mexicana and T. cruzi in vitro (IC50s = 6.2 and 17.5 μM, respectively), inhibits influenza A replication (EC50s = 0.3-1 μM), and inhibits hepatitis B and hepatitis C virus replication (EC50 = 0.15 μM for both).2,3,4

References
1. de Carvalho, L.P.S., Lin, G., Jiang, X., et al. Nitazoxanide kills replicating and nonreplicating Mycobacterium tuberculosis and evades resistance. J. Med. Chem. 52(19), 5789-5792 (2009).
2. Chan-Bacab, M.J., HernÁndez-NÚ•ez, E., and Navarrete-VÁzquez, G. Nitazoxanide, tizoxanide and a new analogue [4-nitro-N-(5-nitro-1,3-thiazol-2-yl)benzamide; NTB] inhibit the growth of kinetoplastid parasites (Trypanosoma cruzi and Leishmania mexicana) in vitro. J. Antimicrob. Chemother. 63(6), 1292-1293 (2009).
3. Rossignol, J.F., La Frazia, S., Chiappa, L., et al. Thiazolides, a new class of anti-influenza molecules targeting viral hemagglutinin at the post-translational level. J. Biol. Chem. 284(43), 29798-29808 (2009).
4. Korba, B.E., Montero, A.B., Farrar, K., et al. Nitazoxanide, tizoxanide and other thiazolides are potent inhibitors of hepatitis B virus and hepatitis C virus replication. Antiviral Res. 77(1), 56-63 (2008).