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Mechanism of Action
Benznidazole is a nitroimidazole antiparasitic with good activity against acute infection with Trypansoma cruzi, commonly referred to as Chagas Disease. Like other nitroimidazoles, benznidazole's main mechanism of action is to generate radical species which can damage the parasite's cellular machinery. The mechanism by which nitroimidazoles do this seems to depend on whether or not oxygen is present. This is particularly relevant in the case of Trypanosoma species, which are considered facultative anaerobes.

Under anaerobic conditions, the nitro group of nitroimidazoles is believed to be reduced by the pyruvate:ferredoxin oxidoreductase complex to create a reactive nitro radical species. The nitro radical can then either engage in other redox reactions directly or spontaneously give rise to a nitrite ion and imidazole radical instead. The initial reduction takes place because nitroimidazoles are better electron acceptors for ferredoxin than the natural substrates. In mammals, the principal mediators of electron transport are NAD+/NADH and NADP+/NADPH, which have a more positive reduction potential and so will not reduce nitroimidazoles to the radical form. This limits the spectrum of activity of nitroimidazoles so that host cells and DNA are not also damaged. This mechanism has been well-established for 5-nitroimidazoles such as metronidazole, but it is unclear if the same mechanism can be expanded to 2-nitroimidazoles (including benznidazole).

In the presence of oxygen, by contrast, any radical nitro compounds produced will be rapidly oxidized by molecular oxygen, yielding the original nitroimidazole compound and a superoxide anion in a process known as "futile cycling". In these cases, the generation of superoxide is believed to give rise to other reactive oxygen species. The degree of toxicity or mutagenicity produced by these oxygen radicals depends on cells' ability to detoxify superoxide radicals and other reactive oxygen species. In mammals, these radicals can be converted safely to hydrogen peroxide, meaning benznidazole has very limited toxicity to human cells. In Trypansoma species, however, there is a reduced capacity to detoxify these radicals, which results in damage to the parasite's cellular machinery.

Pharmacokinetics
Oral benznidazole has a bioavailability of 92%, with a peak concentration time of 3-4 hours after administration. 5% of the parent drug is excreted unchanged in the urine, which implies that clearance of benznidazole is mainly through metabolism by the liver. Its elimination half-life is 10.5-13.6 hours.

Interactions
Benznidazole and other nitroimidazoles have been shown to decrease the rate of clearance of 5-fluorouracil (including 5-fluorouracil produced from its prodrugs capecitabine, doxifluridine, and tegafur). While co-administration of any of these drugs with benznidazole is not contraindicated, monitoring for 5-fluorouracil toxicity is recommended in the event they are used together.

The GLP-1 receptor agonist lixisenatide may slow down the absorption and activity of benznidazole, presumably due to delayed gastric emptying.

Because nitroimidazoles can kill Vibrio cholerae cells, use is not recommended within 14 days of receiving a live cholera vaccine.