The purpose of the study was to investigate the pharmacokinetics of cefquinome in plasma and milk samples of lactating Chinese Holstein following a single intramammary administration into one quarter at the dose of 75 mg. Residue depletion of cefquinome in milk administrated at one quarter following three consecutive infusions at the same dose were also carried out. Cefquinome concentrations in plasma and milk were determined by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method. A non-compartmental analysis was used to obtain the pharmacokinetic parameters of cefquinome. Following the single treatment, cefquinome wasn’t detected in any of the plasma samples. The concentration of cefquinome in milk reached peaked values (Cmax) of (599.00±322.00) μg mL-1 at 2 h after administration (Tmax), elimination half-life (t1/2λz) was (4.63±0.26) h, area under the concentration-time curve (AUC0-∞) was (4 890.19±1 906.98) μg mL-1 h, and mean residence time (MRT) was (6.03±2.27) h. In residue depletion study, cefquinome concentrations in 5 out of 6 milk samples at 72 h were lower than the maximum residue limit fixed by the European regulatory agency (20 μg kg-1 for cefquinome) and cefquinome still could be detected in milk of treated quarters at 120 h post-treatment. The maximum concentration (Cmax) of cefquinome in milk from treated quarters was (486.50±262.92) μg mL-1 and arrived at 6 h after administration (Tmax), elimination half-life (t1/2λz) was (6.30±0.76) h, area under the concentration-time curve (AUC0-∞) was (44747.79±11434.43) μg mL-1 h, and mean residence time (MRT) was (10.09±1.40) h. This study showed that cefquinome has the feature of poor penetration into blood and was eliminated quickly from milk in lactating cows after intramammary administration.

The pharmacokinetics of quinocetone and its major metabolites in healthy swine was investigated in this paper.Quinocetone was administered to 8 healthy cross-bread swine intravenously and orally at a dosage of 4 and 40 mg kg-1body weight respectively in a randomized crossover design test with two-week washout period. A sensitive highperformanceliquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was developed for thedetermination of quinocetone and its metabolite 1-desoxyquinocetone in plasma. Plasma concentration versus timeprofiles of quinocetone and its metabolite 1-desoxyquinocetone were analyzed by non-compartmental analysis usingWinnonlin 5.2 software. Mean maximum concentrations (Cmax) for quinocetone was found to be (0.56±0.13) μg mL-1 at 2.92 h,after oral administration of quinocetone. Mean maximum concentrations (Cmax) for 1-desoxyquinocetone after intravenousor oral administration of quinocetone were (0.0095±0.0012) μg mL-1 at 0.083 h and (0.0067±0.0053) μg mL-1 at 3.08 h. Theapparent elimination half-lives (T1/2) for quinocetone and its metabolite 1-desoxyquinocetone were (2.24±0.24) and(5.23±0.56) h after intravenous administration of quinocetone and (2.91±0.29) and (11.85±2.89) h after oral administrationof quinocetone, respectively. Mean areas under the plasma concentration-time curve (AUC0- ) for quinocetone and 1-desoxyquinocetone were (2.02±0.15) and (0.2±0.002) μg h mL-1 respectively after intravenous administration of quinocetone,and (3.5±0.79) and (0.053±0.03) μg h mL-1 after oral administration of quinocetone, respectively. Quinocetone was rapidlyabsorbed and metabolized in swine after oral and intravenous administration. The plasma concentration-time curve(AUC0- ) of 1-desoxyquinocetone were much smaller than those of quinocetone, while the elimination half-lives (T1/2) weremuch longer than those of quinocetone after intravenously (i.v.) or oral administration.

The present study was carried out to investigate the pharmacokinetics of mequindox (MEQ), a new synthetic quinoxaline 1,4-dioxide derivative and its two main metabolites M1 [2-isoethanol mequinoox], M2 [2-isoethanol 1-desoxymequindox] in healthy swine. MEQ (10 mg kg-1 body weight) was administered to nine healthy cross-bread swine via oral, intramuscular, and intravenous routes in a randomized 3×3 crossover design with a 1-wk washout period. A sensitive high-performance liquid chromatography (HPLC) method was used for the determination of plasma concentrations of MEQ and its metabolites M1 and M2. Plasma concentration versus time profiles of MEQ and its metabolites, M1 and M2, were analyzed by noncompartmental analysis using WinNonlin 5.2 software. The mean maximum concentrations (Cmax) of M1 and M2 after intravenous administration of MEQ were (5.27±1.59) μg mL-1 at 1.78 h and (1.01±0.29) μg mL-1 at 0.92 h, respectively. The mean maximum concentrations (Cmax) of MEQ, M1, and M2 were found to be (6.96±3.23), (6.61±1.56), and (0.78 ±0.25) μg mL-1, respectively at 0.15, 1.61, and 1.30 h after intramuscular administration of MEQ, respectively and (0.75±0.45), (6.90±1.52), and (0.62±0.21) μg mL-1, respectively at 0.40, 1.57, and 2.00 h, respectively after oral administration of MEQ. The apparent elimination half-lives (t1/2) of MEQ, M1, and M2 were (0.84±0.35), (7.57±3.93), and (9.56±6.00) h, respectively after intravenous administration of MEQ; (0.50±0.25), (6.30±3.00), and (5.94±2.54) h, respectively after intramuscular administration of MEQ; and (1.64±1.17), (5.59±1.93), and (16.25±10.27) h , respectively after oral administration of MEQ. The mean areas under the plasma concentration-time curve (AUC0- ) of MEQ, M1, and M2 were (4.88±1.54), (36.93±17.50), and (5.16±1.94) μg h mL-1, respectively after intravenous administration of MEQ; (4.18±0.76), (48.25±20.82), and (4.88±2.21) μg h mL-1 , respectively after intramuscular administration of MEQ; and (1.01±0.40), (48.83±20.71), and (5.54±2.23) μg h mL-1, respectively after oral administration of MEQ. MEQ was rapidly absorbed and metabolized in swine after oral, intramuscular, and intravenous administration. Further studies are required to investigate the double-peak phenomenon observed in the plasma concentration-time profile after oral administration and the pharmacokinetics of other metabolites of MEQ.