| In this paper, an in vitro pharmacokinetics-pharmacodynamics model(PK-PD model) and an ex vivo PK-PD model of doxycycline against Aeromonas hydrophila(A.h) were investigated. There were the following four main elements:1. The minimum inhibitory concentration(MIC) and minimum bactericidal concentration(MBC) of doxycycline against A.h in extract broth and serum were experimented. We used the micro dilution. In consequence, the accurate MIC and MBC of doxycycline against A.h in extract broth were 2.0μg/mL and 8.0μg/mL, and the MBC/MIC ratio was 4. The MICscrum of doxycycline against A.h in serum were 2.0μg/mL. It concluded that doxycycline has high bactericidal activity to A.h in different medium.2. A simple Ultra Performance Liquid Chromatography(UPLC) with UV detecion method for the determination of doxycycline in extract broth and serum. The samples were extracted with perchloric acid, then extracts were centrifuged and the supernatant was sent to UPLC-UV after purified by 0.22μm filter.5μL extract was separated on a reversed phase C18 reversion chromatographic colunmn(1.7μm,2.1×50 mm) at 45℃, which was then eluted with 0.01 mol/L sodium dihydrogen phosphate-acetonitrile(4:1) at a flow of 0.300 mL/min. The UV detection was atλ350nm.The standard curve of doxycycline at the concentration range of 0.05-10μg/L was linear (r=0.9999). The calibration curve equation of doxycycline in in extract broth and serum were y=17120x-103.29(r2=0.9999) and y=13779x+1284.9(r2=0.9997). At fortification levels of 0.1,1,10μg/mL, mean recoveies ranged from 91.78-94.25% for extact broth, 89.42-93.27% for serum. The limit of detection were both 3μg/L.3. An in vitro PK-PD model of doxycycline against A.h was established. We simulated pharmacokinetic process of fish by a airtight container which was pumped in and out broth at the same time, and learnt the pharmacodynamic effect of doxycycline by detecting the number of A.h at different time. And then the PK-PD relationship was researched. In consequence, In the in vitro model with elimination half-life of 38.63 h, A.h was inhibited for only 3 h by 2 MIC doxycycline, and A.h regrew after the model worked about for 3 h.4,8 and 16 MIC doxycycline showed continously inhibitive action on A.h. It concluded that the inhibiting effect of doxycycline against Aeromonas hydrophila was closely related to its concentration, and continous inhabitation could be achieved at the condition of Cmax/MIC>3.96.4. An ex vitro PK-PD model of doxycycline against A.h was established. For the rational usage of doxycycline to treat the haemorrhagic septicemia of channel catfish(Ictalurus punctatus), the integration of pharmacokinetics in vivo and pharmacodynamics ex vivo was used to study the antibacterial activity of doxycycline against A.h in channel catfish serum ex vivo. The data were analyzed with the pharmacokinetic computer program kinetica 4.4 and 3p97. The results indicated that doxycycline was absorbed fast and eliminated slowly after oral administration(20 mg/kg), the Cmax was 1.72μg/mL at 2.57 h, Elimination half-life (T(1/2)β)was 38.63 h. EC50 was 16.95 h. The PK-PD model parameter Cmax/MICserum was 0.86, AUC0→24h/MICscrum was 20.57 h. We estimated the optimal dose ranged from 10.68 to 41.42 mg per kilo of body weight through the Inhibitory Effect Sigmoid Emax.The conclusion is that when doxycycline was employed to treat the haemorrhagic septicemia of channel catfish, dosage regime should be fed mixed feed which contained doxycycline 41.42 mg per kilo of body weight, once a day. When doxycycline was employed to provent the disease, dosage regime should be fed mixed feed which contained doxycycline 10.68 mg per kilo of body weight, once a day. |
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