Nitrofurans

The mechanism of action of nitrofurantoin is unique. It is reduced by bacterial flavoproteins to reactive intermediates that inhibit bacterial ribosomes and other macromolecules. Protein synthesis, aerobic energy metabolism, DNA and RNA synthesis, and cell wall synthesis are inhibited. Nitrofurantoin is bactericidal in urine at therapeutic doses. Resistance is rare. Nitrofurantoin is used to treat urinary tract infections caused by susceptible bacteria, such as Escherichia coli, Staphylococcus aureus, Streptococcus pyogenes, and Aerobacter aerogenes. Proteus spp, Pseudomonas aeruginosa, and Streptococcus faecalis are usually resistant. After administration PO, nitrofurantoin is rapidly and completely absorbed (the macrocrystal form takes longer) and is swiftly eliminated by the kidneys, mainly by tubular secretion (~40% in the unchanged form). Serum concentrations are low, and little unbound drug is available for diffusion into the tissues. The plasma half-life is only ~20 min. Nitrofurantoin is concentrated in acid urine. When the pH reaches ~5, the drug becomes supersaturated without precipitation, and its antibacterial action is maximal. Nitrofurantoin can be administered PO or parenterally. The dosage for dogs and cats is 4.4 mg/kg, PO, tid for 4–10 days. Adverse effects are not common at usual dosages, but nausea, vomiting, and diarrhea can develop. CNS disorders have been seen, and polyneuropathy is a serious effect seen in people. Animals with decreased renal function have a predisposition for polyneuritis. Various manifestations of hypersensitivity reactions can be seen. Yellow discoloration of teeth occasionally has been reported in very young animals.

Nitrofurazone is only slightly soluble in water but, in general, corresponds to nitrofurantoin in terms of its mechanism of action, antimicrobial spectrum, potency, and physicochemical characteristics. Its main indications include the treatment of bovine mastitis, bovine metritis, and wounds. However, pus, blood, and milk reduce the antibacterial activity. Nitrofurazone is also used as a feed additive (0.05%) to control intestinal bacterial and coccidial infections. The withdrawal time for nitrofurazone in pigs is 5 days.

This is a nitrofuran with a wide range of antimicrobial activity that includes Clostridium, Salmonella, Shigella, Staphylococcus and Streptococcus spp, and E coli. It is also active against Eimeria and Histomonas spp. It is usually administered PO to treat intestinal infections but may also be applied topically. The usual oral dose of furazolidone in calves is 10–12 mg/kg, bid for 5–7 days. Caution should be exercised when treating small calves (eg, Jersey breed) to avoid excessive dose rates, lest neurotoxicity result; signs include head tremors, ataxia, visual impairment, and convulsions.

Nifuraldezone, like furazolidone, is used to control bacterial enteritis in calves. Nifurprazine is used only topically as an antibacterial agent. Furaltadone is used both PO to prevent intestinal infections and directly into the teat to treat mastitis.