Pharmacokinetics and ex-vivo pharmacodynamics of cefquinome against Klebsiella pneumonia in healthy dogs

J. vet. Pharmacol. Therap. 37, 37--373. doi:./jvp.. Pharmacokinetics and ex-vivo pharmacodynamics of cefquinome against Klebsiella pneumonia in healthy dogs B. ZHANG X. GU X. LI M. GU N. ZHANG X. SHEN Y. LI & H. DING Laboratory of Veterinary Pharmacology, College of Veterinary Medicine, South China Agricultural University, Guangzhou, China Zhang, B., Gu, X., Li, X., Gu, M., Zhang, N., Shen, X., Li, Y., Ding, H. Pharmacokinetics and ex-vivo pharmacodynamics of cefquinome against Klebsiella pneumonia in healthy dogs. J. vet. Pharmacol. Therap. 37, 37 373. A two-period cross-over study was carried to investigate the pharmacokinetics (PK) and ex-vivo pharmacodynamics (PD) of cefquinome when administrated intravenously (IV) and intramuscularly (IM) in seven healthy dogs at a dose of mg/kg of body weight. Serum concentrations were determined by HPLC-MS/MS assay and cefquinome concentration vs. time data after IV and IM were best fit to a two-compartment open model. Cefquinome mean values of area under concentration time curve (AUC) were 5.5 lgh/ml for IV dose and.59 lgh/ml for IM dose. Distribution half-lives and elimination half-lives after IV dose and IM dose were.7 and. h,.53 and.9 h, respectively. Values of total body clearance (Cl B ) and volume of distribution at steady-state (V ss ) were.9 Lkg/h and.8 L/kg, respectively. After IM dose, C max was.53 lg/ml and the bioavailability was 89.3%. For PD profile, the determined MIC and MBC values against K. pneumonia were.3 and. lg/ml in MHB and.3 and. lg/ml in serum. The ex vivo time-kill curves also were established in serum. In conjunction with the data on MIC, MBC values and the ex vivo bactericidal activity in serum, the present results allowed prediction that a single cefquinome dosage of mg/kg may be effective in dogs against K. pneumonia infection. (Paper received 8 July 3; accepted for publication November 3) Huanzhong Ding, Laboratory of Veterinary Pharmacology, College of Veterinary Medicine, South China Agricultural University, Guangzhou, 5, China. E-mail: hzding@scau.edu.cn INTRODUCTION Cefquinome, an aminothiazolyl cephalosporin, is the fourth generation cephalosporin antibiotic effective against a broad spectrum of bacteria and is highly resistant to b-lactamase (Limbert et al., 99). Cefquinome has been developed solely for veterinary use and is mainly used for the treatment of respiratory tract diseases in cattle, pigs and horses; acute mastitis and foot-rot disease in cattle; and metritis mastitis agalactia syndrome in sows in the European Union since 99 (Committee for Veterinary Medical Products., 995; Committee for Veterinary Medical Products, 999, 3). Due to its high antimicrobial activity against a wide variety of bacteria and being a special veterinary drug, cefquinome seems to have a potential for treating infections caused by bacteria in dogs. In China, cefquinome has been approved for the treatment of bacterial infections in dogs. Pharmacokinetics of cefquinome is characterized by rapid absorption (.5 h), rapid elimination (<3 h), low protein binding (<5%), good bioavailability (>9%), and limited distribution (. L/kg) in piglets, horses, camels, calves, sheep, goats, rabbits, ducks and chickens (Li et al., 8; Winther et al., ; Al-Taher, ; Uney et al., ; Errecalde et al., ; Hwang et al., ; Yuan et al., ; Xie et al., 3). However, pharmacokinetic information of cefquinome in dog is extremely poor. There was only an old publication about pharmacokinetic data of cefquinome in dogs. The elimination half-lives were.85,.98,.9 h, and the volumes of distribution at steady-state (V ss ) were.,.,. L/kg. The total body clearances were 7., 79.3, 7. ml/min/kg when cefquinome was administrated intravenously at three levels dose of 5 mg/kg, mg/kg, and mg/kg, respectively (Limbert et al., 99). Klebsiella pneumonia is a gram-negative bacilli belonging to the Enterobacteriaceae family. It is a widespread colonizer of the animal gut, and it is also known for its ability to survive in the environment and multiply in moist condition. This opportunistic bacterium can cause pneumonia and infections in the urinary tract, skin and soft tissue in healthy animals (Starlander & Melhus, ). In specific cases, judicious antibiotic use 3 John Wiley & Sons Ltd 37

38 B. Zhang et al. has led to considerable reduction in numbers of K. pneumonia; however, the therapy may be limited if the organism produces an extended-spectrum b-lactamase (ESBL). Poirel et al. (3) reported CTX-M-5-producing Klebsiella pneumonias and thought it may evolve separately from the reservoir of CTX-M- 5 producers in companion animals living in the Paris area in France. As a commensal organism in dogs and cats, Klebsiella pneumoniae with ESBL gene, which is resistant to many antibacterial drugs, should be cured by a more b-lactamase-stable new antibacterial. The aim of this investigation were (I) to establish the serum concentration time profile and to derive PK data for cefquinome in dog after IV and IM dose at the manufacturer s recommended dosage mg/kg b.w.; (II) to investigate the MIC and MBC of cefquinome against K. pneumonia ATCC 35 in MHB and dog serum and the ex vivo antibacterial activity of cefquinome in serum against K. pneumonia. MATERIALS AND METHODS Animals and experimental design Seven two-year old healthy dogs (Chinese rural dog, four females, three males) were randomly assigned to two group for a two-period cross-over study. The body weight ranged from to 5 kg. Dogs did not receive any other antimicrobial medication when they grew up. Each dog received cefquinome (cefquinome sulfate injection, 5 mg/ml, Hebei Yuanzheng Pharmaceutical Co., Ltd, China) at a dosage of mg/kg b.w. by IV and IM injection. The dogs were individually housed and fed antibiotic-free dried food twice a day and water was available ad libitum. All animals remained in good health during the studies and were re-homed at the end of study. The animals were humanely handled according to the approved IACUC protocols in South China Agricultural University. In period, four dogs received cefquinome IV injection into the forelimb cephalic vein, and three dogs received the IM injection into the thigh muscle. In the second period, administration routes were reversed. An interval of 7 days elapsed between the periods. Serum concentration time profiles of cefquinome were established after IV and IM dosing. In samples collected at predetermined times after IM cefquinome dosing, the ex vivo antibacterial activity of cefquinome in serum was established against K. pneumonia. In addition, in vitro cefquinome MIC and MBC in serum and Mueller-Hinton broth (MHB) against K. pneumonia were determined. Sampling procedures Blood samples (5 ml) were collected without anticoagulant in plastic tubes prior to and at predetermined times (5,, 5, 3 and 5 min and,,,, 8, and h) after cefquinome administration. Samples were allowed to stand, protected from sunlight, at room temperature for 3 min, then placed on ice for 3 min and centrifuged by g at C for min. Supernatant serum was harvested and stored in aliquots at C prior to measurement of cefquinome concentration and ex vivo antibacterial activity determination. HPLC-MS/MS analysis of cefquinome in serum After thawing at room temperature, an aliquot of 5 ll serum samples were added to microcentrifuge tubes. Subsequently, to all samples, 5 ll of acetonitrile was added and vortexed for 3 s and the samples were centrifuged at g for min. After centrifugation, ll of clear supernatant was pipetted into a fresh tube, 8 ll of water was added. After vortexmixing for 5 s, the samples were filtered through a. lm nylon syringe filter (JinTeng Experiment Equipment Co., Ltd., Tianjin, PR China) into an autosampler vial. The HPLC-MS/MS assay was performed using an Agilent series HPLC and an Agilent 3 Triple quadrupole mass spectrometer equipped with an electrospray ionization source (Agilent Technologies, USA). The chromatographic separation was achieved on a luna C 8 column (5 mm9 mm, 5 lm, Phenomenex Technologies, USA) at 5 C with a thermostated column oven. The mobile phase was solution A (water with.% formic acid, v/v) and solution B (acetonitrile) (8:, v/v), with a thermostated flow rate of.5 ml/min. The injection volume was ll. The mass spectrometric analysis was performed in the positive ion MRM mode at V ion spray voltage (IS). Ion source temperature (TEM) was maintained at C and collision gas (CAD) was 5psi. Sheath gas and auxiliary gas (nitrogen) pressure was 55 psi and psi, respectively. The instrument was operated in multiple reaction monitoring (MRM) mode with the transitions of precursor/product ion pairs m/z 59.3/3. and m/z 59.3/39.. The collision energy (CE) was set at 8 and ev, respectively. The fragment electric voltage was 5v and the dwell time was. s. Retention time for cefquinome was approximately. min. Cefquinome quantification was linear within a range of ng/ml. Linearity of the standard curve was r >.999. The lower limit of quantification (LLOQ) of cefquinome in serum was ng/ml. The intra-assay and interassay repeatability and reproducibility of the method were evaluated using spiked concentrations. Intra-assay and interassay coefficients of variation (CV%) were all less than % and the percentage recovery of cefquinome was 8..3% 3..% (mean SEM, n = 7). Unless otherwise stated, all chemicals and reagents were supplied by Sigma-Aldrich Co. Ltd. Determination of MIC and MBC against K. pneumonia in vitro The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of cefquinome against K. pneumonia ATCC 35 (Nanjing Bianzhen Microbial Sci. & Tech. Co., Ltd, Nanjing, China) were determined by a microdilution method based on CLSI. (8) methodology, but five overlapping sets of doubling dilutions were used to improve accuracy (Potter et al., 3). Ex vivo antimicrobial activity of cefquinome K. pneumonia was grown freshly from beads, previously stored at 7 C, on tryptone soya agar (TSA). Eight to ten colonies were used to inoculate 5 ml MHB and grew overnight at 35 C. Serum samples, collected from dogs which had received IM administration of cefquinome, were used. ll stationary-phase bac- 3 John Wiley & Sons Ltd

Pharmacokinetics and ex-vivo pharmacodynamics of cefquinome in dogs 39 terial cultures were added to ml serum, respectively, to give a final concentration of approximately 9 CFU/mL. To determine viable count, 5 ll serum were added to 5 ll saline (dilution = ) and then was further diluted to achieve dilutions of and. Controls were further diluted to. ll of each dilution were dropped onto MHA. Plates were incubated at 37 C for at least h. The limit of detection was CFU/mL. PK analyses Pharmacokinetic parameters were calculated for cefquinome in serum using the WinNonlin program (Pharsight Corporation, Mountain View, CA, USA). The concentration data were analyzed by Compartmental method and Minimum Akaike Information Criteria Estimates were applied to select the best fitting model (Yamaoka et al., 978). The data were re-weighted to determine improved estimates. Statistical analyses All data are presented as means SEM. Arithmetic means were determined, as appropriate, for each parameter and variable. The SEM for arithmetic means has been included to give an indication of the variability in the data. RESULTS Pharmacokinetics of cefquinome After IM administration of cefquinome, there were no observed adverse effects in dogs, such as tissue irritation, signs of pain, or lameness. The serum cefquinome concentration vs. time data after IV and IM administration were best described by a two-compartment open model. The serum concentration time profiles are illustrated in Fig.. Pharmacokinetic parameters are presented in Table. Absorption, distribution and elimination of cefquinome were rapid after IM administration: the absorption half-life (t /ka ) was.5 h and the mean time to peak (t max ) was.7 h; the distribution half-life (t /a ) was. h, similar to the value of IV dose (.7 h); the elimination half-life (t /b ) was.9 h, while t /b for IV administration was.53 h. The area under Concentration (μg/ml).. IV observed IV predicted IM observed IM predicted 8 8 Fig.. Cefquinome concentration-time profiles plotted arithmetically for serum after i.v. and i.m. administration. The predicted values of IV and IM administration by a two-compartment open model. Values are means SD (n = 7). concentration time curve (AUC - ) was 5.5 lgh/ml (IV) and.59 lgh/ml (IM). The value of volume of distribution at steady-state (V ss ) was.8 L/kg after IV administration and the bioavailability (F) was 89.3% after IM administration. MIC, MBC and the in vitro time-kill curves The protein binding rate (<%) of cefquinome in dogs serum was determined firstly. The MIC and MBC against K. pneumonia ATCC 35 were.3 lg/ml and. lg/ml in MHB,.3 lg/ml and. lg/ml in serum. Specially, the mutant prevention concentration (MPC) against K. pneumonia ATCC 35 in MHB was determined and the value was.8 lg/ml. Onthe whole, the in vitro time-kill curves in serum for eight multiples of MIC (.5 ) indicated a timedependent killing action of cefquinome (Fig. ), with minor differentiations in the rate and extent of bacterial killing when drug concentration rose from to 9 MIC. Cefquinome concentration of.5 9 MIC yielded a slight reduction of the bacterial density. A rise of cefquinome concentration to 9 MIC yielded a bactericidal effect. A further increase in cef- Table. Pharmacokinetic variables for cefquinome in serum after i.v. and i.m. administration (arithmetic mean and SEM, n = 7): two-compartmental modeling Variable (units) Intravenous Arithmetic mean SEM Intramuscular Arithmetic mean SEM A(lg/mL) 5.8.5..3 B(lg/mL).55.5.. a (h )..8.. b (h ).9.3.3.9 K a (h ).5.558 K (h ).8..8.77 K (h ).85.878.3.357 K (h ).7.7.7.79 V (L/kg).3.3 V /F (L/kg).7.85 V ss (L/kg).8. t /a (h).7.5..59 t /b (h).53.53.9.5 t /ka (h).5.3 C max (lg/ml).53. t max (h).7.5 AUC - (lgh/ 5.5.8.59.5398 ml) Cl B (Lkg/h).9.3 Cl B /F (Lkg/h).3.87 F (%) 89.3 A, zero-time intercept of distribution slope in the compartment model; B., zero-time inter of decline in plasma concentration of drug; a, distribution rate constant; b, elimination constant; K a, absorption constant; K, the central compartment elimination constant; K and K, the first-order rate constants; V, volume of distribution of the central compartment; V /F, V scaled to bioavailability; V ss, volume of distribution at steady state; t /a, distribution half-life. t /b, elimination half-life; t /ka, absorption half -life; C max, maximum concentration; t max, the time to peak; AUC -, area under serum concentration-time curve to infinity; Cl B, clearance rate; Cl B /F, clearance scaled to bioavailability. F, bioavailability. 3 John Wiley & Sons Ltd

37 B. Zhang et al. quinmone concentration up to 9 MIC produced a maximal killing, with higher concentrations providing little added benefit. Cefquinome ex vivo antibacterial activity in serum The ex vivo antibacterial time-kill curve for cefquinome in serum against K. pneumonia ATCC 35 was illustrated at eleven time points using samples collected before and between.83 and h after administration (Fig. 3). Cefquinome samples collected between.83 and 8 h after drug administration from all animals exerted a dramatically bactericidal effect (- Log CFU/mL reduction) after 9 h of incubation. Slightly inhibition of bacterial growth (-Log CFU/mL reduction) was observed in h sample and no inhibition of bacterial growth was observed in h sample. The bactericidal activity (defined as the log reduction in bacterial population compared with the initial inoculum log CFU/mL after h incubation) was represented in Fig. (in the MHB) and Fig. 5 (in the serum), respectively. The mean bactericidal activity value in serum samples, after a -h exposure, was 5. after a dosage of mg/kg IM administration. DISCUSSION Pharmacokinetics of cefquinome A two-compartment open model after single IV dosage regimen were also reported in sheep (Uney et al., ), piglets (Li et al., 8), ducks (Yuan et al., ), buffalos (Dinakaran et al., 3) and chickens (Xie et al., 3). The V ss, an indication of the diffusion of the drug into the body tissue, of cequinome in dogs was.8 L/kg, which was higher than. L/kg in piglets (Li et al., 8),. L/kg in sows (Block et al., 5),. L/kg in buffalo calves (Dinakaran et al., 3),. L/kg in horses (Prescott, ),.3 L/kg in sheep (Uney et al., ),. L/kg in rabbits (Hwang et al., ) and.9 L/kg in chicken (Xie et al., 3). Generally, the V ss from various species animals Bacterial count Log (CFU/mL) 8.5 MIC MIC MIC MIC 8 MIC MIC 3 MIC MIC 5 5 5 3 Bactericidal activity 5 3 MIC MIC MIC 8 MIC MIC 3 MIC MIC 5 5 5 3 Fig.. In vitro time-kill curves for cefquinome concentration range 9 MIC against K. pneumonia in dog serum. Fig.. Relationship between bactericidal activity, cefquinome concentration, and incubation time for K. pneumonia ATCC 35 with MIC of.3 lg/ml in MHB. The bactericidal activity is the log reduction in bacterial population compared with the initial inoculum log CFU/mL after h incubation. Bacterial count Log (CFU/mL) 8 5 5 5 3.83 h.5 h.5 h h h h h 8 h h h Fig. 3. Ex vivo inhibition of bacterial growth in serum before and after i.m. administration of cefquinome (sampling times of.83, 5,.5,,,,, 8, and h). Values are means (n = 7). SEM bars not included for clarity. Bactericidal activity 5 3.83.5.5 8 5 5 5 3 Fig. 5. Relationship between bactericidal activity, cefquinome concentration, and incubation time for K. pneumonia ATCC 35 with MIC of.3 lg/ml in serum. 3 John Wiley & Sons Ltd

Pharmacokinetics and ex-vivo pharmacodynamics of cefquinome in dogs 37 existed at low values, which indicated that cefquinome probably distributed mainly in the plasma compartment. The clearance rate (Cl) of cefquinome in dog (.9 Lkg/h) in this study was higher than.8.3 Lkg/h in piglets, sows, wild boars, sheep, goats, rabbits, ducks and chicken (Song et al., 3; Block et al., 5; Uney et al., ; Errecalde et al., ; Hwang et al., ; Yuan et al., ; Xie et al., 3). These limited distributions and low clearance rate of cefquinome in the various species could be attributed to low fat solubility, protein binding activity and its pka values of.5.9 (Hwang et al., ; Zhang et al., 7). In addition, the elimination half-life (t /b ) was.53 h, similar to those in ducks (.57 h) (Yuan et al., ), longer than those in calves (.33 h) (Limbert et al., 99), chickens (.9 h) (Xie et al., 3), rabbits (.93 h) (Hwang et al., ), sheep (.78 h) (Uney et al., ), but shorter than those in piglets (.85 h) (Li et al., 8), buffalo calves (3.5 h) (Dinakaran et al., 3). A two-compartment model with first order absorption best described the drug concentration time data after single IM administration. The mean elimination half-life (t /b ) value after IM administration was.9 h, which was similar to those described in sheep (.85 h) (Uney et al., ), ducks (.79 h) (Yuan et al., ), shorter than those described in piglets (.3 h) (Li et al., 8), pigs (.9 h) (Lu et al., 7), camels (. h) (Al-Taher, ), but longer than those described in chickens (.35 h) (Xie et al., 3), rabbits (. h) (Hwang et al., ). Cefquinome was rapidly absorbed with a C max of.53 lg/ml achieved at.7 h after IM administration. The bioavailability was calculated to be 89.3% after IM administration, while high bioavailability was also reported in calves, horses, piglets, sheep, rabbits, ducks and chickens (Limbert et al., 99; Errecalde et al., ; Allan & Thomas, ; Li et al., 8; Uney et al., ; Hwang et al., ; Yuan et al., ; Xie et al., 3). Pharmacodynamics of cefquinome As valuable extendedspectrum drugs for treatment of serious human infections, the fourth-generation cephalosporins are not first-choice antimicrobial agents in veterinary clinic. To minimize the selection pressure of resistant bacteria, fourth-generation cephalosporins should be reserved for use where susceptibility testing indicates that alternatives are not available (Prescott, ). Cefquinome is developed solely for veterinary use and is licensed in Europe for the treatment of bovine respiratory disease (Zhang et al., 7). In China, cefquinome has been approved for the treatment of bacterial infections in dogs and cats. In order to avoid indiscriminant use of new antimicrobial agents in companion animals, it is more appropriate to choose narrow-spectrum (less broad-spectrum) antibacterial agents specifically active against particular pathogens associated with the certain infections. However, with the increasing prevalent ESBL gene resistant strains in veterinary and human clinic, the present b-lactam antibiotics displayed less ability in killing those isolates which carried ESBL-resistant gene. From a clinical point of view, cefquinome should be used for serious infections resistant to other drugs in animals. Plasma protein binding prevents the antimicrobial actions of antimicrobial drugs. In the present investigation, MIC values for cefquinome were almost the same in serum (.3 lg/ml) and MHB (.3 lg/ml). This is likely to reflect the low degree of protein binding of cefquinome in dog serum (<%, data was determined in another experiment in our laboratory). Normally, there are other differences in composition (such as protein content) between MHB and serum. It is therefore strongly preferable to determine MICs in biological fluid matrices when the objective of the study is the prediction of an effective dose for clinical use (Sidhu et al., ). The present in vitro and ex vivo data in serum demonstrated that cefquinome produced maximal killing when concentrations are maintained at 9 MIC, with higher concentrations providing little added benefit. The time-kill kinetic profiles showed an initial rapid decrease of viable counts, followed by a slower decrease between and h of exposure to the antibiotic. Our data confirm previous reports that cephalosporins in general and cefquinome in particular exert time-dependent killing of bacteria. Because cefquinome is a beta-lactam antimicrobial and acts as a time-dependent bactericidal drug (Thomas et al., ), the most appropriate PK/PD parameter to describe drug efficacy is the time during which the drug s concentration exceeds the MIC (T>MIC) (McKellar et al., ; Zonca et al., ). It is generally recommended that T>MIC should be at least 5% of the dosage interval to ensure an optimal bactericidal effect (Winther et al., ). During the present study, to optimize the cefquinome dosage regimen, we assessed the MIC (.3 lg/ml) on K. pneumonia in dog serum and calculated the T>MIC ( h) at a dose of mg/kg after IM administration. The MIC 9 collected from literature data on Klebsiella spp. (3 strains) was.3 lg/ml (Zonca et al., ) and the T>MIC 9 was h. Rational administration of cefquinome Optimizing dosage schedules of antimicrobial drugs is crucial in ensuring bacteriological and clinical cures and minimizing the emergence of resistance (Drusano, 3; Lees et al., ; Fabrega et al., 8). As MIC defines efficacy and potency for the whole bacterial populations and not for subpopulations, It is limited to prevent the resistance emerge only by considering the PK-PD integration indices AUC h /MIC, C max /MIC and T>MIC. Indeed, there is limited correlation between the value of T>MIC and the probability of drug resistance development (Sidhu et al., ). The mutant prevention concentration (MPC), the upper limit of the mutant selection window, is the drug concentration which blocks the growth of the least susceptible, single-step mutant (Drlica, 3). Another interpretation of MPC is the MIC of resistance strains. The T>MPC was h when the MIC was changed to MPC in this trial, which suggested that the dosage should be added and the interval should be curtailed. Compared with in vivo trial, bacteria is continuous-exposed to a fixed concentration of agent for a defined time ( h) in an ex vivo trial, without considering differences in inoculum size and host defence mechanisms. However, ex vivo data pro- 3 John Wiley & Sons Ltd

37 B. Zhang et al. vide a useful indication of antibacterial activity and might be used to predict the outcome of treatment, as in the present investigation. To further determine dosage for treating dog respiratory infections caused by K. pneumonia, additional data are required. Firstly, data on MIC 5 and MIC 9 for a reasonable number of strains of this species are needed. Secondly, information on T>MIC values is required to achieve end-points for further strains of K. pneumonia. Thirdly, the PK properties of drugs may differ between the healthy subjects (normally of the same breed and similar age/weight) used in preclinical studies and the more variable population of clinical subjects, additionally with disease of varying incidence and severity. Fourthly, generally speaking, the cefquinome does not penetrate well enough into the interstitium or bronchial secretions, which are target tissues; so studies assessing the concentration and activity of this drug in the serum may not really reflect its effect in these tissues and some PK parameters such as V ss may not be a definitive refection of distribution into the respiratory secretions. In future study, we wish this question may be resolved by a tissue-cage model or microdialysis technology. Finally, it is recognized that drug concentrations required to achieve bacteriological cure and prevention of enrichment of resistant mutants depend on inoculum size. In this study, MIC, MBC and bacterial kill curves were determined using a moderate inoculum load of 9 CFU/mL. In future studies, it will be desirable to devise T>MIC surrogates by PK-PD modelling based on both lighter and heavier inoculum loads. In conclusion, results of the present study indicated that cefquinome is highly active against K. pneumonia, and single IM administration of mg/kg every h can maintain the cefquinome concentration over the MIC of K. pneumonia up to h in dog serum. However, estimation of drug dosage requires () determination of MIC 9 of each pathogenic species in dogs, and () establishing the PK PD integration of the drug with the T>MIC parameter to determine rational recommend dose for the clinical therapy. ACKNOWLEDGMENTS This paper is supported by the Natural Science Foundation of China (Grant No.373). REFERENCES Allan, M.J. & Thomas, E.. Pharmacokinetics of cefquinome after parenteral administration of an aqueous solution in the horse. 8th Congress European Association, Veterinary Pharmacology and Toxicology, July, Lisbon, Portugal: Abs.53. Al-Taher, A.Y. () Pharmacokinetics of cefquinome in camels. Journal of Animal and Veterinary Advances, 9, 88 85. Block, C.V., Wanner, M. & Heinritzi, K. 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