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The study was carried out to characterize the pharmacokinetics after intravenous (iv, 20 ㎎/㎏) and oral (p.o. 100 ㎎/㎏) administration as oxytetracycline (OTC) and tiamulin (TIA) mixture in swine and to determine interaction between OTC and TIA against various pig pathogenic bacteria. The antibacterial effects of OTC in combination with TIA in vitro showed synergistic effect against Salmonella typhimurium 1925, Pasteurella multocida Type A, P. multocida Type D, Krebsiella Pneumoniae 2001, K. Pneumoniae 1560, K. Pneunoniae 2208, Haemophillus pleuropneumonia S 2, and H. pleuropneumonia S 5, but against additive effect E. coli K88ab and S. choleraesuis on the basis of fractional inhibitory concentration (FIC) index. On the while, after i.v. and p.o. administration of OTC and TIA mixture, each OTC and TIA concentrations in plasma were fitted to an open two-compartment model. After i.v. administration of OTC-TIA mixture, the mean distribution half-life (T_1/2α) of OTC and TIA in plasma showed 0.29 h and 0.17 h, and the mean elimination half-life (T_1/2β) of those was 4.36 h and 6.64 h, respectively. The mean volume of distribution at steady state (Vd_ss) of OTC and TIA was 0.85 ℓ/㎏ and 2.44 ℓ/㎏, respectively. After oral administration of OTC and TIA mixture, the mean maximal absorption concentrations (C_max) of OTC and TIA were 0.60 ㎍/㎖ at 1.07 h (T_max) and 1.68 ㎍/㎖ at 1.85 h (T_max), respectively. The mean elimination half-life (T_1/2β) of those showed 6.84 h and 6.36 h. In conclusion, we could suggest in this study that the combination of OTC and TIA may be recommended for the antibacterial therapy against polymicrobial infections, and both OTC and TIA showed large distribution to tissues and high C_max after p.o. administration.
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