Nifurtimox is a nitrofuran derivative used as a primary agent in the treatment of American trypanosomiasis (Chagas' disease) caused by Trypanosoma cruzi, especially in the acute, early stage of the disease. The efficacy of nifurtimox in the treatment of chronic Chagas' disease varies from one country to another, possibly due to variation in the sensitivity of different strains of the organism. Nifurtimox has also been used to treat African trypanosomiasis (sleeping sickness) and is active in the second stage of the disease (central nervous system involvement). When nifurtimox is given on its own, about half of all patients will relapse, but the combination of melarsoprol with nifurtimox appears to be efficacious. Nifurtimox forms a nitro-anion radical metabolite that reacts with nucleic acids of the parasite causing significant break down of DNA. Nifurtimox undergoes reduction and creates oxygen radicals such as superoxide. These radicals are toxic to T. cruzi. Mammalian cells are protected by the presence of catalase, glutathione, peroxidases, and superoxide dismutase. Accumulation of hydrogen peroxide to cytotoxic levels results in parasite death. Side effects occur following chronic administration, particularly in elderly people. Major toxicities include immediate hypersensitivities such as anaphylaxis and delayed hypersensitivity reaction involving icterus and dermatitis. Central nervous system disturbances and peripheral neuropathy may also occur.