Agriculture Reference
In-Depth Information
nitrofuran drug furaltadone. It has been shown that a proportion of the bound
residues of furazolidone and furaltadone possess intact side-chains each of
which has molecular characteristics in common with the parent compounds
[42].
Previous studies [43] have indicated that, in animal tissue, these side-chain
residues persist longer than their intact parent compounds [44].
As parent compounds metabolize rapidly after ingestion to form the
corresponding tissue bound metabolites [15] who remains in the body many
weeks after treatment, it is nowadays common practice to analyze animal
tissues and other animal products, like eggs, for the presence of nitrofurans by
detection of their protein-bound, side-chain metabolites (Figure1) AOZ,
AMOZ, AHD, SEM and DNSH by their released after by mild acid hydrolysis
and monitored as marker residues [20, 42, 45-46].
A number of bioavailability studies have been conducted on veterinary
drug residues in the past. However, these have almost invariably consisted of
measuring total tissue radioactivity in rats that had been fed with tissue from
animals that had been treated with 14 C-labelled drugs. This approach, while
demonstrating that incurred residues of a particular drug are bioavailable, does
not usually permit the identification of the chemical compound responsible for
that radioactivity [15].
Studies examining the bioavailability of nitrofuran metabolites have
demonstrated the possibility of residual transfer to secondary species. When
rats were fed pig tissue containing radio-labelled ( 14 C) furazolidone, 41% of
the total amount consumed was made bioavailable to the rat [15].
Bioavailability can occur through the ingestion of contaminated meat and
animal products (such as eggs), even after cooking [47-48], as well as by
transfer to the progeny of hens [44, 49-50] emphasizing the health risk for
consumers. It is currently unclear for how long tissue-bound residues of the
nitrofuran drugs may be detected in edible tissues after cessation of
medication. The pharmacokinetics of AOZ residues in pig tissues have been
the subject of various studies. These suggested that:
a) Tissue-bound AOZ residues persist for at least six weeks post-
withdrawal;
b) Tissue-bound AOZ residues have a longer half-life than solvent
extractable AOZ residues [28, 42]; and
c) The highest AOZ concentrations are to be found in liver tissue but
that AOZ in muscle tissue exhibits a longer depletion half-life
[28, 43].
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