Sulphonamide residues in milk of dairy cows following intravenous injection

Transfer of sulphamethazine from contaminated dairy feed to cows' milk

Four groups of four healthy mid-lactation Friesian cows were fed a compound feeding stuff containing either 2, 10 or 250 mg sulphamethazine/kg, corresponding to 0, 2, 10 and 250 per cent of the therapeutic inclusion rate in rations for pigs, at a flat rate of 3 kg twice daily for 21 days, followed by a seven-day withdrawal period. The cows were machine-milked twice daily and pooled milk samples from each cow were analysed by a commercially available microbiological assay with a sensitivity of 100 micrograms/litre and by a high performance liquid chromatography (HPLC) procedure with a limit of detection of 10 micrograms/litre. No sulphamethazine was detected by HPLC in the milk samples taken from any of the cows fed the concentrate containing 2 or 10 mg/kg. The milk samples from all four cows fed the highest concentration of sulphamethazine contained from 21 to 120 micrograms/litre while they were being fed the contaminated concentrate. The cow with the highest concentrations of sulphamethazine was the only one which repeatedly tested positive by the microbiological assay. The concentration of sulphamethazine declined rapidly during the withdrawal period and the drug was not detectable by either method in samples taken from two days after the contaminated feed was withdrawn.

Sulphonamide and dapsone residues in bovine milk following intramammary infusion

The elimination into bovine milk of sulphonamides (sulphadimidine and sulphamethoxypyridazine) and dapsone following intramammary infusion was studied. Determination of sulphonamides and dapsone in milk was performed by a high performance liquid chromatographic method with UV detection. The limit of quantification was 0.01 microgram/ml. Withdrawal times were established considering the maximum residue limits fixed by the European Community (100 micrograms/kg for sulphonamides and 25 micrograms/kg for dapsone). The diffusion of residues into milk from a quarter infused by the intramammary route to the untreated quarters was also studied.

High-performance liquid chromatographic method for the routine determination of sulphadimidine, its hydroxy metabolites and N4-acetylsulphadimidine in body fluids and cell culture media

A simple high-performance liquid chromatographic method is presented for the determination of trace amounts of sulphadimidine (SDD), its hydroxylated metabolites and N4-acetyl-SDD in blood plasma, urine, hepatocyte culture media and microsomal incubations. The synthesis of 5-hydroxy-SDD and an improved method for the isolation of 4-methylhydroxy-SDD from urine are described and their respective specific absorption coefficients at 265 nm are calculated by on-line radiochemical and ultraviolet detection. The limit of detection of the analytical method is 0.05 micrograms/ml for SDD and its hydroxy metabolites and 0.2 micrograms/ml for N4-acetyl-SDD. Linear calibration graphs for SDD and its metabolites were constructed from 0.2 to 50 micrograms/ml. The method has been applied to biotransformation studies in vivo and in vitro.