Fexinidazole is an antiparasitic drug, which is in the phase III of clinical trial for the treatment of Human African Trypanosomiasis, and in the phase II for the treatment Disease, Chagas and Visceral Leishmaniosis. However, for the Visceral Leishmaniosis, studies were terminated, due to lack of efficacy. Fexinidazole rapidly metabolized to two active metabolites, a sulfone and a sulfoxide, which prolong the pharmacological action of parent drug. These metabolites retaine trypanocidal activity but are less effective in nifurtimox-resistant lines, which can lead to the potential danger in the use of fexinidazole as a monotherapy.