The prevalence and possible causes of bound and extractable residues of the furazolidone metabolite 3‐amino‐2‐oxazolidinone in porcine tissues

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Abstract
Furazolidone is readily metabolized and rarely detectable in animal tissues. An alternative is to measure bound and extractable residues containing the 3‐amino‐2‐oxazolidinone (AOZ) moiety. This compound was used to examine the incidence of furazolidone residues in Northern Ireland pigs. AOZ was found in 32/200 kidney samples. A depletion study showed that none of the samples contained AOZ residues at concentrations greater than that found in pigs fed medicated feed, and subjected to an obligatory 7‐day withdrawal period. Furazolidone carry‐over from medicated feed to subsequent unmedicated batches of feed was investigated in a local feed mill. Furazolidone could be detected only in the first two batches of ostensibly unmedicated feed. A series of feeds containing levels of furazolidone similar to those found in the feed mill carry‐over study were prepared. These were fed to pigs, which were killed without withdrawal. The tissues contained AOZ residues, but at concentrations lower than those found in pigs fed medicated feed and properly withdrawn. The possible cross‐contamination of unmedicated pigs following exposure to a cleaned house that had previously housed pigs undergoing furazolidone medication was investigated. Tissue AOZ residues were detected, even after comparatively short periods of exposure. However, the concentrations were again lower than those found in pigs fed medicated feed and properly withdrawn.