Determination of the presence of 10 antimicrobial residues in Mexican pasteurized milk

Residues of 9 antimicrobial agents approved in Mexico for veterinary use in dairy cattle (sulfathiazole, sulfamerazine, sulfamethazine, sulfachloropyridazine, sulfamonomethoxine, sulfamethoxazole, nitrofurazone, furaltadone, and furazolidone) and non-approved chloramphenicol residues were studied every two weeks in four commercial brands of Mexican pasteurized milk (A, B, C and D) during one year (n=4x24=96). Drug residues were analyzed by high pressure liquid chromatography HPLC with UV detection. Percentage of positive samples to sulfonamide residues were 47.2% (Milk A), 58.3% (Milk B), 44.7% (Milk C) and 50% (Milk D). Sulfonamide residues ranged between 1.9 and 180 mu g/kg. sulfathiazole and sulfamerazine were the most common residues found. Only three samples (Milk B) exceeded maximum residue levels established for sulfonamides. Nitrofuran residues were not detected in any milk sample. Illegal Chloramphenicol residues were detected in one milk sample (Milk A) in levels of 27.2 mu g/kg.