Abstract:

 This experiment was conducted to study tissue residues of ceftiofur in swine, preparing for determination of the withdrawal time. A confirmative method has been improved to determine ceftiofur residues in edible tissues of pigs by high-performance liquid chromatography (HPLC). Ceftiofur was administered to 30 healthy pigs intramuscularly at a dosage of 5 mg·kg^－1 for 3 consecutive days. Animals were sacrificed at 12 hours and the 3rd, 5th, 7th, 9th days after administration. The tissues were extracted with dithioerythritol, derivatized with iodoacetamide, and cleaned up on MCX solid-phase extraction cartridges. The analyte was detected by UV absorptive spectroscopy after separation by C₁₈ column. The results showed that kidney had the highest drug concentration with 2.589 μg·g^－1 at 12 hours, while the concentration of ceftiofur in all of tissues at 3 days was lower than the Maximum Residue Limit (MRL). The pharmacokinetic parameters were estimated using Winnonlin software package. The results indicated that the elimination rate was skin/fat﹥muscle﹥liver﹥kidney﹥injection site, with the elimination half-life of 28.99, 35.80, 36.76, 55.72, 160.8 h respectively. Compared with other tissues, the area under concentration-time curve (AUC) in kidney was highest with 123.4 h·μg·g^－1. Kidney was considered as the target organ. According to the MRL set by EU, the longest withdrawal time was suggested in injection site with 98.64 h. The results demonstrated that absorption and elimination was quickly and the distribution was wide. It is proposed that the withdrawal time was 5 days.