Nitrofurans and nitroimidazoles
Nitrofurans
Nitrofurans with a NO2 group bound to a nucleus furan have a bacteriostatic effect against Gram-negative organisms like Escherichia coli. Bacteria reduce NO2 groups faster than the human cells and only the reduced metabolites damage DNA. This explains why nitrofurans have few effects on human cells.
Nitrofurans such as nifuroxazide (Ercefuryl*) - because they are poorly absorbed after oral intake- are used in the treatment of bacterial diarrhea. They have few adverse effects however they can cause different allergic manifestations.
The nitrofuran indicated in the treatment of uncomplicated urinary bacterial infections is nitrofurantoin (Furadantin*). Well absorbed by digestive tract, it is eliminated in high concentration in urine. It can cause some digestive adverse effects, nausea, vomiting, diarrhea, hepatitis; blood disorders: leukopenia, anemia; nervous disorders: headache, dizziness. Nitrofurantoin can give a brownish color to urines.
Nitroimidazoles
Nitroimidazoles are active against anaerobic microorganisms like Clostridium, Fusobacterium, Streptococcus, Bacterioides, against parasites like Trichomonas vaginalis, Giardia intestinalis, Entamaeba histolytica, which have enzymatic equipment able to transform nitroimidazoles into toxic reduced derivatives which damage DNA. The nitrated group accepts electrons from flavoproteins and ferrodoxines of these microorganisms and parasites. The derivatives of nitro-5-imidazole having this spectrum of activity are metronidazole (Flagyl*), ornidazole (Tiberal*), tinidazole (Fasigyn*). In animal experiments, metronidazole potentiates the effect of x-rays.
Secnidazole, tenonitrozole and nimorazole are marketed only in a few countries.
Nitroimidazoles can give a disulfiram-like effect, or “antabuse” effect, when treated patients take alcohol; the symptoms,are flushing, headache… On prolonged therapy, they can give neutropenia and peripheral neuropathy. Metronidazole does not seem teratogenic in pegnant women.
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