On Determination Of Cephapirin Benzathine And Cephalonium Residues In Milk And Withrdawal Time For Milk Of Their Intrammary Infusion

Cephapirin (CEPP) and Cephalonium (CEPL) are the first generation semi-synthetic cephalosporin with a broad spectrum of activity against both Gram-negative and Gram-positive bacteria, which are used to prevent and treat cow’s subclinical and clinical mastitis caused by sensitive bacteria in cows at drying off. The study was conducted to develop a residual detection method for determination of cephapirin and its metabolite desacetyl cephapirin (DCEPP), Cephalonium. In addition, the residue depletion of cephapirin benzathine and cephalonium in bovine milk was preliminary researched by the method established.1. Simultaneous determination of cephapirin and cephalonium in milk by HPLC-MS/MSThe drug in milk sample was extracted and deproteined with acetonitrile. The extract was cleaned up by SPE with Oasis HLB cartridge. Waters XBridgeTM C18(4.6x150mm,5μm) was used as the analytical column, and a gradient elution with methanol and water (containing0.005%formic acid) as the mobile phase. Quantification was carried out by positive electrospray ionization (ESI+) and selected reaction monitoring (SRM) mode. The recoveries at the spiked level of1,10,100,400μg/kg were between81.17%-100.81%, inter-day CV was between1.85-11.36%%, intra-day CV was between2.58-11.49%. The concentration of CEPP, DCEPP, CEPL in milk showed a good liner relation within the range of5-400μg/kg, and the linear correlation coefficients were0.9999. The LOD of cephapirin, desacetyl cephapirin and cephalonium was0.5μg/kg. The LOQ of cephapirin, desacetyl cephapirin and cephalonium was1μg/kg.2. The withdrawal time for milk of cephapirin benzathine and cephalonium in milkFour healthy Holstein cows during the dry period were used in residue depletion study. Cephapirin benzathine was administered by the intramammy route at a dose of300mg/quarter in2cows, which calved48and58days later respectively. Cephalonium was administered by the intramammary route at a dose of300mg/quarter in other two cows, which calved49and93days after infusion respectively. Milk residue depletion was studied with HPLC-MS/MS, and the marker of residue was detected after the1st,2nd,3rd,4th,5th,6th,7th,8th,9th,10th milking. The results showed the concentrations of CEPP and CEPL were lower than the LOD (0.5μg/kg) of the method established. Meanwhile it was far below the MRLs recommended by EMEA (10μg/kg). According to the usual methods of calculation for the withdrawal time in our country, the withdrawal time for milk of cephapirin benzathine and cephalonium intrammary infusion was advised as0day in cow.