The nitrofurans are a group of synthetic broad-spectrum antibiotics, which have been widely and effectively used for the prevention and treatment of gastrointestinal infections caused by Escherichia coli, Salmonella spp., Mycoplasma spp., Coccidia spp., coliforms and other protozoa in animal production and aquaculture. Moreover, nitrofurans have been employed as growth promoters in livestock.
Four major Nitrofurans
The four major nitrofurans are furazolidone, furaltadone, nitrofurantoin and nitrofurazone. They have been banned in the EU for use as veterinary drugs, due to their toxic an suspected carcinogenic and mutagenic properties (Commission Regulation 1442/95). In 2003 a definitive MRPL (Minimum Required Performance Limit) was set at 1 ng/g in the EU for the above mentioned four nitrofurans in poultry and aquaculture products (Commission Decision 2003/181/EC).
Various studies have demonstrated that the nitrofuran parent molecules are rapidly metabolised by animals and that their in vivo stability is not longer than a few hours. As a result, persistent protein-bound residues are formed. Unlike the parent molecules, these protein-bound metabolites are stable and persistent in the body. It is possible to free these residues from proteins by acid hydrolysis. Testing for the presence of nitrofurans is thus equivalent to testing for the presence of a part of the parent molecule, i.e. the free residue. Nitrofuran residues are found after administration of furaltadone (3-amino-5-morpholinomethyl-2-oxazolidinone = AMOZ), furazolidone (3-amino-2-oxazolidinone = AOZ), nitrofurantoin (1-aminohydantoïne = AHD) and nitrofurazone (semicarbazide = SEM).