Metabolism of thiazopyr in laying hens

Thiazopyr labeled with C-13/C-14 was found to be rapidly metabolized and eliminated by laying hens dosed orally for four consecutive days at either 1.3 or 10.4 mg/day. Over 90% of the total radioactive dose appeared in the excreta within 22 h after the final dose at both levels. Tissue residues were very low in the muscle and egg white (0.004-0.01 ppm) with somewhat higher levels observed for the liver, abdominal fat, skin with fat, egg yolk, and kidney (0.047-0.298 ppm). The most abundant tissue metabolite was a nitrile ester resulting from the breakdown of the thiazoline ring of thiazopyr. A carboxylic acid metabolite found in the liver and excreta was shown to arise from oxidation at C-3 of the isobutyl side chain of the nitrile ester. In vitro liver homogenate studies demonstrated the presence of similar metabolic pathways in hens, goats, and rats, although the levels of individual metabolites varied.