Metabolism and depletion of nifursol in broilers

Nifursol has recently been prohibited for use as a feed additive. Considering the similarity in structure between nifursol and the other nitrofurans, an analogous metabolism could be expected. To study the formation of tissue-bound residues in poultry, broilers were treated orally with nifursol during a period of 7 consecutive days, via medicated feed at a dosage of 50 mg/kg feed. Muscle, kidney, liver, bile and plasma samples were collected at the day of cessation of medication (day 0) and at days 3, 7, 14 and 21 after the end of medication. Samples were analysed for nifursol and the acid-hydrolysable side-chain of nifursol (DNSH; 3,5-dinitro salicylhydrazide). Samples were also analysed for the ratio between free (solvent-extractable) metabolites and tissue-bound (non-extractable) metabolites. The results obtained clearly indicate the formation of tissue-bound residues in poultry. Concentrations of non-extractable residue at zero withdrawal time averaged to 900 µg/kg in liver tissue, 2000 µg/kg in kidney tissue, 225 µg/kg in muscle tissue, 1000 µg/kg in bile and 1000 µg/kg in plasma. Taking into account an LoD of 1 µg/kg, non-extractable residues of DNSH can be detected for at least 3 weeks after administration in liver, kidney, bile and plasma and for up to 2 weeks in muscle tissue. The amounts of extractable residues were relatively low, in many instances less than 10% of the total amount of residue. In general terms the depletion data obtained show a similar behaviour of nifursol in broilers as previously found for furazolidone and furaltadone in broilers.