Toltrazuril sulfone is an active metabolite of the coccidiostat toltrazuril .1 Toltrazuril sulfone is formed from toltrazuril via the intermediate metabolite toltrazuril sulfoxide by cytochrome P450 (CYP) enzymes, including CYP3A. It inhibits T. gondii tachyzoite production in African green monkey kidney cells when used at concentrations of 0.1, 1, and 5 ?g/ml.2 Toltrazuril sulfone completely prevents infection with T. gondii tachyzoites in a mouse model of fatal toxoplasmosis when administered at doses of 10 or 20 mg/kg one day prior to, and daily for 10 days following, infection. It also reduces the number of infected mice in the same model when administered at a dose of 10 mg/kg for 11 days starting six days following infection. Formulations containing toltrazuril sulfone have been used in the treatment of equine protozoal myeloencephalitis (EPM) in horses.
1.Benoit, E., Buronfosse, T., Moroni, P., et al.Stereoselective S-oxygenation of an aryl-trifluoromethyl sulfoxide to the corresponding sulfone by rat liver cytochromes P450Biochem. Pharmacol.46(12)2337-2341(1993) 2.Mitchell, S.M., Zajac, A.M., Davis, W.L., et al.Efficacy of ponazuril in vitro and in preventing and treating Toxoplasma gondii infections in miceJ. Parasitol.90(3)639-642(2004)