4-epioxytetracycline and N-demethyloxytetracycline, as metabolites of oxytetracycline (OTC), 4-epitetracycline and N-demethyltetracycline, as metabolites of tetracycline (TC), and 4-epichlortetracycline, isochlortetracycline (ICTC), 4-epi-ICTC, and N-demethyl-ICTC, as metabolites of chlortetracycline (CTC), were detected in egg yolk and plasma obtained from feeding studies with either OTC, TC, or CTC. In egg white, only OTC, TC with its 4-epimer, and ICTC with its 4-epimer were detected in substantial concentrations. The ratios of epimerization and N-demethylation in the eggs did not change during the medication period. The samples were analyzed by an automated HPLC system (ASTED) with UV, fluorescence, or MS-MS detection.
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