Study On Residue Depletion Of Tilmicosin Phosphate In Swine Tissues

Tilmicosin is a novel macrolide antibiotic with a wide therapeutic uses against bacteria and mycoplasma. It has high antibacterial effects and low toxicity or adverse effect, and it shows promising prospect of application in clinical veterinary practice.Tilmicosin phosphate is obtained by chemical reaction of tilmicosin. The tilmicosin and 3,5-dimethyl piperidine can generate chemical reaction, which reacts with the phosphoric acid and water. Although the effective ingredient is tilmicosin, the tilmicosin phosphate is highly soluble in water, and has special antibacterial activity and pharmacokinetic characteristics so it has widely used in veterinary clinic. Although there are some reports about residue depletion of tilmicosin phosphate in swine tissues. Tilmicosin phosphate soluble powder has been modified the durg formulation, So there is a need for further research focusing specifically on its residues in swine tissues. In this study, a high-performance liquid chromatography (HPLC) method was developed for the determination of tilmicosin residues and for the detectiojn of its residue depletion regularity patterns in swine tissues.To understand the tissue residues of tilmicosin phosphate in swine and formulate the determination of the withdrawal time. HPLCmethod with detection at 280 nm was modified and validated for the determination of 10% tilmicosin phosphate soluble powder residues in pig tissues. The mobile phase was composed of acetonitrile, tetrahydrofuran, phosphate buffer and ultrapure water with which the volume ratio was 10:5:5:80 (v:v). Tilmicosin was extracted from swine tissues using acetonitrile and 0.1mol/L potassium dihydrogen phosphate buffer (pH2.5).The tissue extracts were applied to C18 solid-phase extraction (SPE) cartridge.The residue was eluted from SPE cartridge with methanol-acetonitrile-ammonium acetate (20:80:0.77, v:v:g).The standard product was added to the control tissues at 0.05 μg/g,0.5 μg/g,5 μg/g concentrations, the average recoveries were 97.82%,81.81%; 88.67% in liver, and 92.82%,92.87%,90.24% in kidney. Coefficients of variation for liver and kindney were 3.72%～8.17% and 1.05%～10.5% respectively. The standard product added for muscle, skin and subcutaneous fat was at 0.02μg/g,0.2μg/g,2μg/g, the average recoveries were 96.09%,89.64%,77.56% in muscle, and 91.57%,96.21%,81.15%, in subcutaneous fat and skin.Coefficients of variation for muscle and subcutaneous fat and skin were 2.34% ～8.99% and 0.78%～8.87% respectively. The limits of detection (LOD) was 0.025μg/g, and the limits of quantitation (LOQ) was 0.05μg/g for both liver and kidney; the LOD was 0.01μg/g and the LOQ was 0.02μg/g for muscle, subcutaneous fat and skin.Administrated over 7-day by 80 mg/L of Tilmicosin Phosphate in drinking water, the residue levels were higher in liver and kidney, and lower in muscle, subcutaneous fat and skin. According to the calculation by software WT1.4, the withdrawal period of tilmicosin residues was 5.73 d in liver,3.75 d in kidney,11.57 d in muscle,10.91 d in subcutaneous fat and skin. It is concluded that the expected withdrawal period of tilmicosin phosphate for swine should be 12 days.