ANTIPROTOZOAL EFFECTS Nifurtimox and benznidazole are trypanocidal against both the trypomastigote and amastigote forms of T. cruzi. Nifurtimox also has activity against T. brucei and can cure early- and late-stage disease.
The trypanocidal action of nifurtimox derives from its ability to undergo activation by partial reduction to nitro radical anions. Transfer of electrons from the activated drug then forms superoxide radical anions and other reactive oxygen species. Reaction of free radicals results in lipid peroxidation and membrane injury, enzyme inactivation, and DNA damage. Benznidazole also requires a one-electron transfer that generates nitro anion radicals, leading to cellular damage that kills the parasites.
ABSORPTION, FATE, AND EXCRETION
Nifurtimox is well absorbed after oral administration, with peak plasma levels observed after ~3.5 hours. Less than 0.5% of the dose is excreted in urine. The elimination t/2 is ~3 hours. High concentrations of several unidentified metabolites are found, and nifurtimox undergoes rapid biotransformation, probably via a presystemic first-pass effect. Whether the metabolites have any try-panocidal activity is unknown.
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