DETERMINATION OF TRIMETHOPRIM AND SULFADOXINE RESIDUES IN PORCINE TISSUES AND PLASMA

Healthy gilts and market-ready hogs were administered a single intramu scular (IM) injection of Borgal, a commercial formulation of trimethop rim-suifadoxine (TMP-SDX), once or twice daily. The objectives were to determine if a newly-developed high-performance liquid chromatographi c (HPLC) method would be suitable for measuring the residual concentra tions of TMP in the plasma of these live animals, and to determine if the administration of this veterinary drug would leave measurable resi dues in their plasma and tissues at slaughter. Plasma and tissue conce ntrations of SDX and TMP from these animals were determined over a per iod of 14 d using thin-layer chromatography/densitometry (TLCD), and t he newly-developed HPLC method, respectively. The lowest detectable li mit (LDL) for SDX in plasma and tissue was 20 ppb by TLCD. The HPLC me thod had a LDL bf 5 ppb for TMP in plasma and tissue. Both methods wer e then used to provide baseline data on the absorption and depletion o f TMP and SDX from these healthy animals. It was observed that both TM P and SDX were readily absorbed into the blood and tissues, but TMP wa s eliminated much faster than SDX. No TMP residues were detected in th e plasma of any of the gilts at and beyond 21 h after drug administrat ion. Also, no TMP residues were detected in the plasma of any of the m arket-ready hogs 24 h after drug administration at either the label do se or twice the label dose. Sulfadoxine residues at concentrations abo ve the maximum residue limit (MRL) of 100 ppb were, however, detected in the plasma, muscle, kidney, liver, and injection sites of hogs slau ghtered 1 and 3 d after a single IM administration at the label dose. Although SDX residues were still detectable in the lungs, kidney, live r and plasma of some hogs 10 d after administration of the label dose and twice the label dose, these were below the MRL. Postmortem examina tion revealed necrosis and inflammation at the injection sites, but no visible deposits of the injected drug.