Sulphamethazine residue depletion study in piglets after oral administration

The depletion profile of sulphamethazine (SMZ) was studied in healthy piglets after oral administration of a premix, containing 100 g SMZ/kg, at a rate of 1 kg/t of feed for 30 consecutive days. A total of 50 piglets were used in the experiment, 42 of which received the medication and the remaining 8 acted as control animals. The piglets were of 42 days of age and of a mean bodyweight of 28 kg at the beginning of the experiment. Six medicated and one control piglet were sacrificed at days 5, 10, 15, 20, 25, 30 and 35 after the cessation of the treatment and muscle, liver, kidney and fat tissues were sampled and stored at −75 °C pending analysis. The samples were analysed using a liquid chromatographic method, which was fully validated for SMZ residue analysis prior to use. Quite high mean concentrations of SMZ residues of 3.84 mg kg−1 for muscle, 8.14 mg kg−1 for liver, 6.42 mg kg−1 for kidney and 2.88 mg kg−1 for fat tissues were attained 5 days post-medication. SMZ residues were still detected even 20 days post-medication at levels higher than 1.12 mg kg−1 in all tissues examined. In descending order, the SMZ residues concentrations found in all examined tissues were liver > kidney > muscle > fat. The time needed for the concentration of SMZ to drop below the EU established MRL of 100 μg/kg, was 30 days. The statistically estimated withdrawal period was calculated to be 41 days.