Presence of antimicrobial residues in edible pig tissues after exposure to cross-contaminated feed: a case study with sulphadimethoxine/trimethoprim

When manufacturing oral premixes, cross-contamination may occur between medicated and non-medicated feed leading to the exposure of food-producing animals to low concentrations that may result in antimicrobial residues in edible products. This project was designed to assess the level of antibiotic residues in edible pig tissues, faeces and plasma after exposure for 12 days to feed contaminated with sulphadimethoxine/trimethoprim (2% of the therapeutic dosage). Our results show that sulphadimethoxine concentrations can significantly exceed the maximum residue limits (MRL) in liver (618 ± 96 µg/kg) and kidneys (510 ± 73 µg/kg), and that putative metabolites can also be detected in the liver. Based on tissue and plasma data, a pharmacokinetic model was developed to assess which contamination rates would not result in residue concentrations above the MRL. Our simulations show that the contamination rate should remain below 0.2% of the therapeutic dose, i.e. far lower of the tolerated contamination rate.