Ex Vivo Pharmacokinetic And Pharmacodynamic Analysis Of Tulathromycin Against Pasteurella Multocida In Piglets

In this study,an ultra-high-pressure liquid chromatography tandem mass spectrometry(UPLC-MS/MS)method was developed for the determination of tulathromycin in serum,transudate and exudate.The pharmacokinetics properties of tulathromycin were studied for serum,transudate,and exudate using a tissue cage model.To fully understand the antimicrobial characteristic of tulathromycin against Pasteurella multocida(P.multocida)in serum,transudate and exudate.Thus,the ex vivo PK/PD model of tulathromycin against P.multocida was established and added the PK/PD data in order to provide a rational basis for designing dosage regimen.Tulathromycin concentrations in serum,transudate and exudate were determined by UPLC-MS/MS method.Roxithromycin was selected as the internal standard and the drug was extracted by the acetonitrile.Recoveries of tulathromycin in the biological samples were >85% and coefficients of variation were < 10% for both within runs and between runs.The limits of detection(LOD)was 0.5 ng/m L and the limit of quantification(LOQ)was 1 ng/m L.The results indicated that this method was rapid and sensitive,which could satisfy with the study of the pharmacokinetics properties.The MICs of tulathromycin against P.multocida CVCC430 were 0.25 μg/m L in MHB,0.03 μg/m L in serum,transudate and exudate.The MBCs were 0.25 μg/m L in MHB,0.06 μg/m L in serum,transudate and exudate.Especially,the mutant prevention concentration(MPC)against P.multocida CVCC430 was determined and the value was 1.6 μg/m L.The piglets were randomly divided into two groups(TB1 and TB2),with 6 piglets in each group.After tissue cages had been implanted,tulathromycin 2.5 mg/kg body weight was administered via the i.m.route to animals in groups TB1 and by i.v.route to animals in groups TB2.The concentration of tulathromycin in serum,transudate and exudate were determined by UPLC-MS/MS and the concentration-time datas were analyzed by the Win Nolin software.Drug concentration vs.time data after i.v.administration was analyzed by noncompartmental model.The main pharmacokinetics parameters were as follows: t1/2β = 71.326 h,AUClast = 15.947 μg·h/m L,Vd = 17.409 L/kg.The Tmax values of transudate and exudate were 4.500 h and 8.50 h,respectively.The Cmax values of transudate and exudate were 0.102 μg/m L and 0.145 μg/m L,respectively.Drug concentration vs.time data after i.m.administration was analyzed by noncompartmental model.The main pharmacokinetics parameters were as follows: Cmax = 0.740 μg/m L,t1/2β = 63.548 h,Tmax = 0.25 h,AUClast = 16.317 μg·m L/h,F = 104.27 %.The Tmax values of transudate and exudate were 21.500 h and 8.000 h,respectively.The Cmax values of transudate and exudate were 0.053 μg/m L and 0.115 μg/m L,respectively.The ex-vivo growth inhibition datas after i.m.administration were fitted to the Inhibitory effect sigmoid Emax(Hill)equation to provide values for serum of AUC24h/MIC producing antibacterial activity,bactericidal activity and virtual eradication of bacteria of P.multocida CVCC430 in serum which were 44.55 h,73.19 h and 92.44 h,respectively.Combined with the literature reported MIC90 of P.multocida isolated from pigs,the calculated corresponding dosages of tulathromycin to achieve the 99% max response in serum for the MIC90 of 0.12 μg/m L would be 13.25 mg/kg b.w..