ISO-CHLORTETRACYCLINE AND EPI-ISO-CHLORTETRACYCLINE ARE THE PRINCIPALMETABOLITES OF CHLORTETRACYCLINE IN THE HEN EGG

Chlortetracycline (CTC) is a broad spectrum antibiotic, licensed for u se without any withdrawal period, in chickens laying eggs intended for human consumption. In the European Union, a maximum residue limit (MR L) in eggs of 200 mu g/kg for the sum of the concentrations of CTC and its 4-epimer (4-epi-CTC) has been established. Two major CTC metaboli tes have been identified in eggs. These compounds, iso-CTC and 4-epi-i so-CTC, have never previously been shown to be significant products of CTC metabolism in poultry or in any other species. The total amount o f CTC present in eggs, as all of the chemical forms measured, can exce ed the MRL by anything up to a factor of four (170-820 mu g/kg). (C) 1 998 Elsevier Science B.V. All rights reserved.