Comparative pharmacokinetics of norfloxacin nicotinate in common carp (Cyprinus carpio) and crucian carp (Carassius auratus) after oral administration

Comparative pharmacokinetics of norfloxacin nicotinate (NFXNT) was investigated in common carp (Cyprinus carpio) and crucian carp (Carassius auratus) after a single oral dose of 10 mg/kg body weight (b.w.). Analyses of plasma samples were performed using ultra‐performance liquid chromatography (UPLC) with fluorescence detection. After oral dose, plasma concentration–time curves of common carp and crucian carp were best described by a two‐compartment open model with first‐order absorption. The pharmacokinetic parameters of common carp were similar to those of crucian carp. The distribution half‐life (t_1/2α), elimination half‐life (t_1/2β), peak concentration (C_max), time‐to‐peak concentration (T_max), and area under the concentration–time curve (AUC) of common carp were 1.58 h, 26.33 h, 6069.79 μg/L, 1.08 h, and 103072.36 h·μg/L, respectively, and those corresponding to crucian carp were 1.36 h, 26.55 h, 9586.06 μg/L, 0.84 h, and 126604.4 h·μg/L, respectively. These studies demonstrated that 10 mg NFXNT/kg body weight in common carp and crucian carp following oral dose presented good pharmacokinetic characteristics.     

Comparative pharmacokinetics of enrofloxacin in healthy and Aeromonas hydrophila‐infected crucian carp (Carassius auratus gibelio)

The comparative pharmacokinetics of enrofloxacin (ENR) and its metabolite ciprofloxacin (CIP) were investigated in healthy and Aeromonas hydrophila‐infected crucian carp after a single oral (p.o.) administration at a dose of 10 mg/kg at 25 °C. The plasma concentrations of ENR and of CIP were determined by HPLC. Pharmacokinetic parameters were calculated based on mean ENR concentrations by noncompartmental modeling. In healthy fish, the elimination half‐life (T_1/2λz), maximum plasma concentration (C_max), time to peak (T_max), and area under the concentration–time curve (AUC) values were 64.66 h, 3.55 μg/mL, 0.5 h, and 163.04 μg·h/mL, respectively. In infected carp, by contrast, the corresponding values were 73.70 h, 2.66 μg/mL, 0.75 h, and 137.43 μg·h/mL, and the absorption and elimination of ENR were slower following oral administration. Very low levels of CIP were detected, which indicates a low extent of deethylation of ENR in crucian carp.     

Sulfadiazine pharmacokinetics in grass carp (Ctenopharyngodon idellus) receiving oral and intravenous administrations

This study aimed to examine the bioavailability (BA) and pharmacokinetic (PK) characteristics of sulfadiazine (SDZ) in grass carp (Ctenopharyngodon idellus) after oral and intravenous administrations. Blood samples were collected at predetermined time points of 0.083, 0.17, 0.5, 1, 2, 4, 8, 16, 24, 48, 72, and 96 hr (n = 6). The samples were extracted and purified by organic reagents and determined by the ultra‐performance liquid chromatography. The software named 3P97 was used to calculate relevant PK parameters. The results demonstrated that the concentration–time profile of SDZ was best described by a one‐compartmental open model with first‐order absorption after a single oral dose. The main PK parameters of the absorption rate constant (K_α), the absorption half‐life (t_{1/2 Kα}), the elimination rate constant (K_e), the elimination half‐life (t_1/2Ke), and the area under concentration–time profile (AUC_0‐∞) were 0.3 1/h, 2.29 hr, 0.039 1/h, 17.64 hr, and 855.78 mg.h/L, respectively. Following intravenous administration, the concentration–time curve fitted to a two‐compartmental open model without absorption. The primary PK parameters of the distribution rate constant (α), the elimination rate constant (β), the distribution half‐life (t_1/2α), the elimination half‐life (t_1/2β), the apparent distribution volume (V_SS), the total clearance (CL), and AUC_0‐∞ were 9.62 1/hr, 0.039 1/hr, 0.072 hr, 17.71 hr, 0.33 L/kg, 0.013 L h^?1 kg^?1, and 386.23 mg.h/L, respectively. Finally, the BA was calculated to be 22.16%. Overall, this study will provide some fundamental information on PK properties in the development of a new formulation SDZ in the future and is partially beneficial for the appropriate usage of SDZ in aquaculture.     

Pharmacokinetics of florfenicol and its metabolite florfenicol amine in crucian carp (Carassius auratus) at three temperatures after one single intramuscular injection

The pharmacokinetic profiles of florfenicol (FF) or florfenicol amine (FFA) in crucian carp were compared at different water temperatures after single intramuscular administration of FF at 10 mg/kg bodyweight. The concentrations of FF and FFA were determined by a high‐performance liquid chromatography method, and then, the concentration versus time data were subjected to compartmental analysis using a one‐compartment open model. At the water temperatures of 10, 20, and 25°C, the peak concentrations (C_maxs) of FF were 2.28, 2.29, and 2.34 μg/ml, respectively, while those of FFA were 0.42, 0.71, and 0.82 μg/ml, respectively. And the absorption half‐life (t_1/2ka) of FF was 0.21, 0.19, and 0.21 hr, while the elimination half‐life (t_1/2kel) was 31.66, 24.77, and 21.48 hr, respectively. For FFA, the formation half‐life (t_1/2kf) was 3.85, 8.97, and 12.43 hr, while the t_1/2kel was 58.34, 30.27, and 21.22 hr, respectively. The results presented here demonstrated that the water temperature had effects on the elimination of both FF and FFA and the formation of FFA. Based on the T > MIC values calculated here, to treat the infections of bacterial with MIC value ≤ 0.5 μg/ml, FF intramuscularly given at 10 mg/kg bodyweight with a 72‐hr interval is sufficient at the water temperature of 10°C, while the intervals of 60 and 48 hr were needed at 20 and 25°C, respectively. But to treat bacterial with higher MIC values, more FF or FF at 10 mg/kg BW but with shorter intervals should be intramuscularly given to the infected fish.     

Pharmacokinetics of cefquinome in crucian carp (Carassius auratus gibelio) after oral,intramuscular, intraperitoneal,and bath administration

The pharmacokinetics (PK) of cefquinome (CEQ) was studied in crucian carp (Carassius auratus gibelio) after single oral, intramuscular (i.m.), and intraperitoneal (i.p.) administration at a dose of 10 mg/kg body weight and following incubation in a 5 mg/L bath for 5 hr at 25°C. The plasma concentration of CEQ was determined using high‐performance liquid chromatography (HPLC). PK parameters were calculated based on mean CEQ concentration using WinNonlin 6.1 software. The disposition of CEQ following oral, i.m., or i.p. administration was best described by a two‐compartment open model with first‐order absorption. After oral, i.m., and i.p. administration, the maximum plasma concentration (C_max) values were 1.52, 40.53, and 67.87 μg/ml obtained at 0.25, 0.23, and 0.35 hr, respectively, while the elimination half‐life (T_1/2β) values were 4.68, 7.39, and 6.88 hr, respectively; the area under the concentration–time curve (AUC) values were 8.61, 339.11, and 495.06 μg hr/ml, respectively. No CEQ was detected in the plasma after bath incubation. Therapeutic blood concentrations of CEQ can be achieved in the crucian carp following i.m. and i.p. administration at a dosage of 10 mg/kg once every 2 days.     

Pharmacokinetics of enrofloxacin after oral,intramuscular and bath administration in crucian carp (Carassius auratus gibelio)

The pharmacokinetics of enrofloxacin (ENR) was studied in crucian carp (Carassius auratus gibelio) after single administration by intramuscular (IM) injection and oral gavage (PO) at a dose of 10 mg/kg body weight and by 5 mg/L bath for 5 hr at 25°C. The plasma concentrations of ENR and ciprofloxacin (CIP) were determined by HPLC. Pharmacokinetic parameters were calculated based on mean ENR or CIP concentrations using WinNonlin 6.1 software. After IM, PO and bath administration, the maximum plasma concentration (C_max) of 2.29, 3.24 and 0.36 μg/ml was obtained at 4.08, 0.68 and 0 hr, respectively; the elimination half‐life (T_1/2β) was 80.95, 62.17 and 61.15 hr, respectively; the area under the concentration–time curve (AUC) values were 223.46, 162.72 and 14.91 μg hr/ml, respectively. CIP, an active metabolite of enrofloxacin, was detected and measured after all methods of drug administration except bath. It is possible and practical to obtain therapeutic blood concentrations of enrofloxacin in the crucian carp using IM, PO and bath immersion administration.     

Pharmacokinetics and tissue residues of moroxydine hydrochloride in gibel carp,Carassius gibelio after oral administration

The pharmacokinetics and tissue residues of moroxydine hydrochloride were studied in gibel carp at water temperature of 15 and 25 °C. Samples (blood, skin, muscle, liver, and kidney) were collected over 10 days after the treatment and analyzed by high‐performance liquid chromatography with an ultraviolet detector. The results indicated that the influence of water temperature on the metabolism of the drug was significant. The plasma concentration–time data of moroxydine hydrochloride conformed to single‐compartment open model at the two water temperatures. There were higher absorption rate (t_1/2ka) and longer elimination half‐lives (t_1/2ke) at 15 °C (4.29 and 15.87 h, respectively) compared with those at 25 °C (3.02 and 4.22 h, respectively). The maximum plasma concentration (C_max) and the time‐point of maximum plasma concentration (T_p) were 2.98 μg/mL and 10.35 h at 15 °C and 3.12 μg/mL and 4.03 h at 25 °C, respectively. The distribution volume (V_d/F) of moroxydine hydrochloride was estimated to be 4.55 L/kg at 15 °C and 2.89 L/kg at 25 °C. The total body clearance (CL_b) of moroxydine hydrochloride was determined to be 0.25 and 0.49 L/(h·kg) at 15 °C and 25 °C, respectively; the areas under the concentration–time curve were 75.89 μg·h/mL at 15 °C and 42.33 μg·h/mL at 25 °C. The depletion of moroxydine hydrochloride in gibel carp was slower with a longer half‐life period, especially at lower water temperature that was tested.     

Pharmacokinetics of orbifloxacin in crucian carp (Carassius auratus) after intravenous and intramuscular administration

The pharmacokinetics of orbifloxacin was studied after a single dose (7.5 mg/kg) of intravenous or intramuscular administration to crucian carp (Carassius auratus ) reared in freshwater at 25°C. Plasma samples were collected from six fish per sampling point. Orbifloxacin concentrations were determined by high‐performance liquid chromatography with a 0.02 μg/ml limit of detection, then were subjected to noncompartmental analysis. After intravenous injection, initial concentration of 5.83 μg/ml, apparent elimination rate constant (λ_z) of 0.039 hr^?1, apparent elimination half‐life (T_1/2λz) of 17.90 hr, systemic total body clearance (Cl) of 75.47 ml hr^?1 kg^?1, volume of distribution (Vz) of 1,948.76 ml/kg, and volume of distribution at steady‐state (Vss) of 1,863.97 ml/kg were determined, respectively. While after intramuscular administration, the λ_z, T _1/2λz, mean absorption time (MAT ), absorption half‐life (T _1/2ka), and bioavailability were determined as 0.027 hr^?1, 25.69, 10.26, 7.11 hr, and 96.46%, respectively, while the peak concentration was observed as 3.11 ± 0.06 μg/ml at 2.0 hr. It was shown that orbifloxacin was completely but relatively slowly absorbed, extensively distributed, and slowly eliminated in crucian carp, and an orbifloxacin dosage of 10 mg/kg administered intravenously or intramuscularly would be expected to successfully treat crucian carp infected by strains with MIC values ≤0.5 μg/ml.     

Pharmacokinetics and bioavailability of flumequine in blunt snout bream (Megalobrama amblycephala) after intravascular and oral administrations

In this study, the pharmacokinetic profile of flumequine (FMQ) was investigated in blunt snout bream (Megalobrama amblycephala) after intravascular (3 mg/kg body weight (b.w.)) and oral (50 mg/kg b.w.) administrations. The plasma samples were determinedby ultra‐performance liquid chromatography (UPLC) with fluorescence detection. After intravascular administration, plasma concentration–time curves were best described by a two‐compartment open model. The distribution half‐life (t_1/2α), elimination half‐life (t_1/2β), and area under the concentration–time curve (AUC) of blunt snout bream were 0.6 h, 25.0 h, and 10612.7 h·μg/L, respectively. After oral administration, a two‐compartment open model with first‐order absorption was also best fit the data of plasma. The t_1/2α, t_1/2β, peak concentration (C_max), time‐to‐peak concentration (T_max), and AUC of blunt snout bream were estimated to be 2.5 h, 19.7 h, 3946.5 μg/L, 1.4 h, and 56618.1 h. μg/L, respectively. The oral bioavailability (F) was 32.0%. The pharmacokinetics of FMQ in blunt snout bream displayed low bioavailability, rapid absorption, and rapid elimination.     

Pharmacokinetics of doxycycline in tilapia (Oreochromis aureus × Oreochromis niloticus) after intravenous and oral administration

The pharmacokinetics of doxycycline was studied in plasma after a single dose (20 mg/kg) of intravenous or oral administration to tilapia (Oreochromis aureus × Oreochromis niloticus) reared in fresh water at 24 °C. Plasma samples were collected from six fish per sampling point. Doxycycline concentrations were determined by high‐performance liquid chromatography with a 0.005 μg/mL limit of detection, then were subjected to noncompartmental analysis. Following oral administration, the double‐peak phenomenon was observed, and the first (C_max1) and second (C_max2) peaks were 1.99 ± 0.43 μg/mL at 2.0 h and 2.27 ± 0.38 μg/mL at 24.0 h, respectively. After the intravenous injection, a C_max2 (12.12 ± 1.97 μg/mL) was also observed, and initial concentration of 45.76 μg/mL, apparent elimination rate constant (λ_z) of 0.018 per h, apparent elimination half‐life (t_1/2λz) of 39.0 h, systemic total body clearance (Cl) of 41.28 mL/h/kg, volume of distribution (Vz) of 2323.21 mL/kg, and volume of distribution at steady‐state (Vss) of 1356.69 mL/kg were determined, respectively. While after oral administration, the λ_z, t_1/2λz, and bioavailability of doxycycline were 0.009 per h, 77.2 h, and 23.41%, respectively. It was shown that doxycycline was relatively slowly and incompletely absorbed, extensively distributed, and slowly eliminated in tilapia, in addition, doxycycline might undergo enterohepatic recycling in tilapia.     

Plasma pharmacokinetics of quinocetone in ducks after oral and intravenous administration

Quinocetone (QCT), an antimicrobial growth promoter, is widely used in food‐producing animals. However, information about pharmacokinetics (PK) of QCT in ducks still remains unavailable up to now. In this study, QCT and its major metabolites (1‐desoxyquinocetone, di‐desoxyquinocetone and 3‐methyl‐quinoxaline‐2‐carboxylic) in ducks were studied using a simple and sensitive UHPLC‐MS/MS assay. Twenty ducks were divided into two groups. (n = 10/group). One group received QCT by oral administration at dose of 40 mg/kg while another group received QCT intravenously at 10 mg/kg. Plasma samples were collected at various time points from 0 to 96 hr. QCT and its major metabolites in duck plasma samples were extracted by 1 ml acetonitrile and detected by UHPLC‐MS/MS, with the gradient mobile phase that consisted of 0.1% formic acid in water (A) and acetonitrile (B). A noncompartment analysis was used to calculate the PK parameters. The results showed that following oral dosing, the peak plasma concentration (C_max) of QCT was 32.14 ng/ml and the area under the curve (AUCINF_obs) was 233.63 (h ng)/ ml. Following intravenous dosing, the C_max, AUCINF_obs and Vss_obs were 96.70 ng/ml, 152.34 (h ng)/ ml and 807.00 L/kg, respectively. These data indicated that the QCT was less absorbed in vivo following oral administration, with low bioavailability (38.43%). QCT and its major metabolites such as 1‐desoxyquinocetone and 3‐methyl‐quinoxaline‐2‐carboxylic were detected at individual time points in individual ducks, while the di‐desoxyquinocetone was not detected in all time points in all ducks. This study enriches basic scientific data about pharmacokinetics of QCT in ducks after oral and intravenous administration and will be beneficial for clinical application in ducks.     

Pharmacokinetics of fluconazole following intravenous and oral administration to koalas (Phascolarctos cinereus)

Clinically normal koalas (n = 12) received a single dose of 10 mg/kg fluconazole orally (p.o.; n = 6) or intravenously (i.v.; n = 6). Serial plasma samples were collected over 24 h, and fluconazole concentrations were determined using a validated HPLC assay. A noncompartmental pharmacokinetic analysis was performed. Following i.v. administration, median (range) plasma clearance (CL) and steady‐state volume of distribution (V_ss) were 0.31 (0.11–0.55) L/h/kg and 0.92 (0.38–1.40) L/kg, respectively. The elimination half‐life (t_1/2) was much shorter than in many species (i.v.: median 2.25, range 0.98–6.51 h; p.o.: 4.69, range 2.47–8.01 h), and oral bioavailability was low and variable (median 0.53, range 0.20–0.97). Absorption rate‐limited disposition was evident. Plasma protein binding was 39.5 ± 3.5%. Although fluconazole volume of distribution (V_area) displayed an allometric relationship with other mammals, CL and t_1/2 did not. Allometrically scaled values were approximately sevenfold lower (CL) and sixfold higher (t_1/2) than observed values, highlighting flaws associated with this technique in physiologically distinct species. On the basis of fAUC/MIC pharmacodynamic targets, fluconazole is predicted to be ineffective against Cryptococcus gattii in the koala as a sole therapeutic agent administered at 10 mg/kg p.o. every 12 h.     

Molecular cloning of type I collagen cDNA and nutritional regulation of type I collagen mRNA expression in grass carp

Grass carp (Ctenopharyngodon idellus) are important Chinese freshwater fish, and in China, the faba bean has been used as the sole food source for grass carp to transform them into crisp grass carp. Because of this, crisp grass carp has become an economically important fish because of its increased muscle hardness. To study the nutritional regulation of type I collagen in faba bean‐fed grass carp, we isolated type I collagen alpha 2 (COL1A2) on the basis of our isolation of COL1A1. The COL1A2 cDNA was found to be 4899 bp in length and included a 4059‐bp coding sequence (CDS) and encoded a polypeptide of 1352 AA. The protein peptide molecular weight was 127.39 kD, and the theoretical isoelectric point was 9.37. The COL1A2 protein possessed five α‐helixes, eight β‐sheets, 16 regions of triple helical repeats, 21 low‐complexity regions, 10 function domains and two zinc‐binding sites; however, no calcium‐binding sites were observed. The mRNA expression of COL1A1 and COL1A2 was assessed in eight tissues (muscle, hepatopancreas, intestine, gills, skin, fin, kidney and spleen) from grass carp and crisp grass carp by semi‐quantitative RT‐PCR. Expression of COL1A1 in the muscle, intestines and skin of crisp grass carp was higher than that in grass carp, and expression of COL1A2 in the muscle, gills, fin and skin of crisp grass carp was higher than that in grass carp. In the muscle of crisp grass carp, expression of COL1A1 and COL1A2 was higher than that in grass carp, which was further confirmed by real‐time PCR, and collagen content also was enhanced. These results demonstrated that type I collagen was closely related to the increased muscle hardness of faba bean‐fed grass carp.     

Pharmacokinetics of tulathromycin after subcutaneous injection in North American bison (Bison bison)

Tulathromycin is approved for the treatment of respiratory disease in cattle and swine. It is intended for long‐acting, single‐dose injection therapy (Draxxin), making it particularly desirable for use in bison due to the difficulty in handling and ease of creating stress in these animals. The pharmacokinetic properties of tulathromycin in bison were investigated. Ten wood bison received a single 2.5 mg/kg subcutaneous injection of Draxxin. Serum concentrations were measured by liquid chromatography–mass spectrometry (LC‐MS) detection. Tulathromycin demonstrated early maximal serum concentrations, extensive distribution, and slow elimination characteristics. The mean maximum serum concentration (C_max) was 195 ng/mL at 1.04 h (t_max) postinjection. The mean area under the serum concentration–time curve, extrapolated to infinity (AUC_0–inf), was 9341 ng·h/mL. The mean apparent volume of distribution (V_d/F) and clearance (Cls/F) was 111 L/kg and 0.4 L/h/kg, respectively, and the mean half‐life (t_1/2) was 214 h (8.9 days). Compared to values for cattle, C_max and AUC_0–inf were lower in bison, while the V_d/F was larger and the t_1/2 longer. Tissue distribution and clinical efficacy studies in bison are needed to confirm the purported extensive distribution of tulathromycin into lung tissue and to determine whether a 2.5 mg/kg subcutaneous dosage is adequate for bison.     

Depletion study and withdrawal period calculation of florfenicol in the crucian carp (Carassius auratus) following multiple intramuscular injections

The previously adopted marker residue for florfenicol (FF) in China was only florfenicol amine (FFA); however, the marker residue has been changed to FF plus FFA since the end of 2017. The previous official withdrawal period determined based on the only concentration of FFA may no longer be suitable. Therefore, the present study aimed to determine the depletion profiles of FF and FFA and further calculate the withdrawal period in the crucian carp (Carassius auratus) based on the new marker residues. Florfenicol was intramuscularly administered at 10 mg/kg bodyweight daily for five consecutive days to crucian carps reared in freshwater at 10°C. After the last dose, plasma and tissue samples were randomly collected from 10 fish at different time points. The FF and FFA concentrations were simultaneously determined by high-performance liquid chromatography (HPLC) with a fluorescence detector and further subjected to noncompartmental analysis. The elimination half-life (h) of FF in different tissues decreased as follows: liver (39.1) > kidney (36.3) > skin plus muscle (34.6) > plasma (31.7), whereas that of FFA decreased as follows: kidney (41.4) > skin plus muscle (39.4) > liver (39.3) > plasma (35.7). Considering a maximum residue limit of 1 μg/g for the total concentration of FF and FFA in the skin plus muscle, a withdrawal period of 6 days was calculated based on the upper limit of the one-sided 95% confidence interval.     

A physiologically based pharmacokinetics model for florfenicol in crucian carp and oral‐to‐intramuscular extrapolation

Yang, F., Sun, N., Sun, Y. X., Shan, Q., Zhao, H. Y., Zeng, D. P., Zeng, Z. L. A physiologically based pharmacokinetics model for florfenicol in crucian carp and oral‐to‐intramuscular extrapolation. J. vet. Pharmacol. Therap.  36 , 192–200. In this study, an oral physiologically based pharmacokinetics (PBPK) model was developed for florfenicol in crucian carp (Carassius auratus). Subsequently, oral‐to‐intramuscular extrapolation was performed and the two models were used to predict florfenicol concentrations in the edible tissues of crucian carp. The oral model gave good predictions in most tissues, except for kidney and liver in which the florfenicol concentrations were underestimated at the later time points. In contrast, using the intramuscular model, the concentrations in the kidney were overestimated at the later time points. Both models had the best predictive ability in the main edible tissue, the muscle. The oral model also accurately predicted the florfenicol concentrations in the muscle after multiple doses. The present study demonstrated the feasibility of predicting florfenicol concentrations in the edible tissues of crucian carp using a route‐to‐route extrapolation method.     

Pharmacokinetics,bioavailability and PK/PD relationship of cefquinome for Escherichia coli in Beagle dogs

The pharmacokinetics and bioavailability of cefquinome in Beagle dogs were determined by intravenous (IV), intramuscular (IM) or subcutaneous (SC) injection at a single dose of 2 mg/kg body weight (BW). The minimum inhibitory concentrations (MIC) of cefquinome against 217 Escherichia coli isolated from dogs were also investigated. After IV injection, the plasma concentration‐time curve of cefquinome was analyzed using a two‐compartmental model, and the mean values of t_1/2α (h), t_1/2β (h), V_ss (L/kg), Cl_B (L/kg/h) and AUC (μg·h/mL) were 0.12, 0.98, 0.30, 0.24 and 8.51, respectively. After IM and SC administration, the PK data were best described by a one‐compartmental model with first‐order absorption. The mean values of t_1/2Kel, t_1/2Ka, t_max (h), C_max (μg/mL) and AUC (μg·h/mL) were corresponding 0.85, 0.14, 0.43, 4.83 and 8.24 for IM administration, 0.99, 0.29, 0.72, 3.88 and 9.13 for SC injection. The duration of time that drug levels exceed the MIC (%T > MIC) were calculated using the determined MIC₉₀ (0.125 μg/mL) and the PK data obtained in this study. The results indicated that the dosage regimen of cefquinome at 2 mg/kg BW with 12‐h intervals could achieve %T > MIC above 50% that generally produced a satisfactory bactericidal effect against E. coli isolated from dogs in this study.     

Pharmacokinetics of chloramphenicol following administration of intravenous and subcutaneous chloramphenicol sodium succinate,and subcutaneous chloramphenicol,to koalas (Phascolarctos cinereus)

Clinically normal koalas (n = 19) received a single dose of intravenous (i.v.) chloramphenicol sodium succinate (SS) (25 mg/kg; n = 6), subcutaneous (s.c.) chloramphenicol SS (60 mg/kg; n = 7) or s.c. chloramphenicol base (60 mg/kg; n = 6). Serial plasma samples were collected over 24–48 h, and chloramphenicol concentrations were determined using a validated high‐performance liquid chromatography assay. The median (range) apparent clearance (CL/F) and elimination half‐life (t_1/2) of chloramphenicol after i.v. chloramphenicol SS administration were 0.52 (0.35–0.99) L/h/kg and 1.13 (0.76–1.40) h, respectively. Although the area under the concentration–time curve was comparable for the two s.c. formulations, the absorption rate‐limited disposition of chloramphenicol base resulted in a lower median C_max (2.52; range 0.75–6.80 μg/mL) and longer median t_max (8.00; range 4.00–12.00 h) than chloramphenicol SS (C_max 20.37, range 13.88–25.15 μg/mL; t_max 1.25, range 1.00–2.00 h). When these results were compared with susceptibility data for human Chlamydia isolates, the expected efficacy of the current chloramphenicol dosing regimen used in koalas to treat chlamydiosis remains uncertain and at odds with clinical observations.     

Cytochemical characterization of peripheral blood cell populations of two Cyprinidae,Carassius auratus and Ctenopharyngodon idellus

Fish are the most diverse species of all vertebrate groups, and their blood cells have shown variable characteristics in terms of morphology. Cytochemical staining for enzyme activity in blood leukocytes will help assess the immune function of fish. We characterize blood cells from crucian carp (Carassius auratus) and grass carp (Ctenopharyngodon idellus) by using a Diff‐Quick stain as well as different cytochemical methods. Blood specimens obtained from crucian carp and grass carp were evaluated after cytochemical staining for acid phosphatase (ACP), alkaline phosphatase (ALP), naphthol AS chloroacetate esterase (AS‐DNCE), naphthyl acetate esterase (NAE), α‐naphthyl butyrate esterase (NBE), peroxidase (MPO) and periodic acid–Schiff's reaction (PAS) using commercial kits. Blood cell types were evaluated based on their morphological characteristics and the presence or absence of specific chromogen. The expression pattern of enzymes was similar between the two Cyprinidae and was also broadly consistent with other fish species. However, there were some interesting differences detected between crucian carp and grass carp, including naphthol AS chloroacetate esterase activity in monocytes, peroxidase activity and location in thrombocytes. The ACP, ALP and MPO expressions of different leukocytes of the two Cyprinidae were evaluated by Image Pro Plus and were analysed for statistical significant differences. This investigation provides basic haematology and enzyme activity analyses for crucian carp and grass carp and serves as an approach to evaluating the immune response of fish.     

Pharmacokinetics of meloxicam in koalas (Phascolarctos cinereus) after intravenous,subcutaneous and oral administration

The pharmacokinetic profile of meloxicam in clinically healthy koalas (n = 15) was investigated. Single doses of meloxicam were administered intravenously (i.v.) (0.4 mg/kg; n = 5), subcutaneously (s.c.) (0.2 mg/kg; n = 1) or orally (0.2 mg/kg; n = 3), and multiple doses were administered to two groups of koalas via the oral or s.c. routes (n = 3 for both routes) with a loading dose of 0.2 mg/kg for day 1 followed by 0.1 mg/kg s.i.d for a further 3 days. Plasma meloxicam concentrations were quantified by high‐performance liquid chromatography. Following i.v. administration, meloxicam exhibited a rapid clearance (CL) of 0.44 ± 0.20 (SD) L/h/kg, a volume of distribution at terminal phase (V_z) of 0.72 ± 0.22 L/kg and a volume of distribution at steady state (V_ss) of 0.22 ± 0.12 L/kg. Median plasma terminal half‐life (t_1/2) was 1.19 h (range 0.71–1.62 h). Following oral administration either from single or repeated doses, only maximum peak plasma concentration (C_max 0.013 ± 0.001 and 0.014 ± 0.001 μg/mL, respectively) was measurable [limit of quantitation (LOQ) >0.01 μg/mL] between 4–8 h. Oral bioavailability was negligible in koalas. Plasma protein binding of meloxicam was ~98%. Three meloxicam metabolites were detected in plasma with one identified as the 5‐hydroxy methyl derivative. This study demonstrated that koalas exhibited rapid CL and extremely poor oral bioavailability compared with other eutherian species. Accordingly, the currently recommended dose regimen of meloxicam for this species appears inadequate.