Pharmacokinetics, Tissue Residues, and Withdrawal Times of Florfenicol in Chukar Partridges (Alectoris chukar)

The aim of this study was to determine pharmacokinetics of florfenicol and its metabolite florfenicol amine after a single (30 mg/kg) intravenous (IV) and oral administration of florfenicol in chukar partridges. It also aimed to investigate tissue residue and withdrawal time of florfenicol after multiple-dose (30 mg/kg, every 24 h for 5 days) oral administration. The research was carried out in two stages: pharmacokinetics and residue. Plasma and tissue concentrations of florfenicol and florfenicol amine were determined by HPLC. The elimination half-life of florfenicol was 5.25 h for IV and 5.44 h for oral. The volume of distribution at a steady state and total body clearance of florfenicol were 0.38 L/kg and 0.07 L/h/kg, respectively, after IV administration. The peak plasma concentration and bioavailability for oral administration were 45.26 ± 4.06 and 51.55%, respectively. After multiple-dose oral administration, the highest concentration was detected in the liver (9.21 μg/g) for florfenicol and in the kidney (0.67 μg/g) for florfeniol amine. The calculated withdrawal period of florfenicol was determined as 6, 3, 4, and 5 days for muscle, liver, kidney, and skin + fat, respectively. These data indicate that a 6-day WT after multiple-dose administration of florfenicol in chukar partridges can be considered safe for human consumption.

Pharmacokinetic characteristics of florfenicol in green sea turtles (Chelonia mydas) and hawksbill sea turtles (Eretmochelys imbricata) after intramuscular administration

The pharmacokinetics of florfenicol (FFC) in green sea and hawksbill sea turtles were evaluated following intramuscular (i.m.) administration at two different dosages of 20 or 30 mg/kg body weight (b.w.). This study (longitudinal design) used 5 green sea and 5 hawksbill sea turtles for the two dosages. Blood samples were collected at assigned times up to 168 h. FFC plasma samples were analyzed using validated high-performance liquid chromatography equipped with diode array detection. The pharmacokinetic analysis was performed using a non-compartment approach. The FFC plasma concentrations increased with the dosage. The elimination half-life was similar between the treatment groups (range 19-25 h), as well as the plasma protein binding (range 18.59%-20.65%). According to the surrogate PK/PD parameter (T > MIC, 2 μg/mL), the 20 and 30 mg/kg dosing rates should be effective doses for susceptible bacterial infections in green sea and hawksbill sea turtles.

The Pharmacokinetics of tilmicosin in plasma and joint dialysate in an experimentally Mycoplasma synoviae infection model

Mycoplasma synoviae (MS) infection is a serious threat to poultry industry in China, thus it is essential to study the pharmacokinetics (PK) in the target site of MS-infected chickens, but there are no relevant reports at present. The aim of this study was to compare the PK of tilmicosin in plasma and joint dialysate in MS-infected chickens. The MS infection model was established by evaluating the influence factors of the susceptibility of chicken species, day age of chicken, infection routes, infection cycle, infection dose, and stress response. The clinical symptoms, pathogen isolation, PCR identification, and ELISA antibody were detected to determine whether the MS infection model has been successfully established. Eight-week-old Mahuang chickens were challenged with MS by joint combined with footpad, 2 mL each time, twice a day for 5 d, then the MS infection model was successfully established. The infection group was orally administrated a single dose of 15 mg/kgbody weight (b. w.) tilmicosin. The joint dialysate was collected by the microdialysis technique, then the concentration of tilmicosin in plasma samples and joint dialysate were determined by triple quadrupole high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). There was no significant difference in elimination half-life (t_1/2) and the mean residence time (MRT) of dialysate and plasma. In contrast, the time of the area under the concentration-time curve (AUC) and the (maximum concentration of tilmicosin in plasma) C_max of tilmicosin in plasma was 2.1 and 1.4 times higher than in dialysate. The distribution coefficient of tilmicosin in joint and plasma (AUC_dialysate/AUC_plasma) was 0.51. In conclusion, tilmicosin concentration in joints of MS-infected chicken was much lower than that of plasma, which may result in the poor clinical effect and drug resistance. The study could provide a reference for the clinical use of tilmicosin against MS.

The influence of the site of drug administration on florfenicol pharmacokinetics in turkeys

Florfenicol is a broad-spectrum antibacterial drug used in the treatment of farm animals, including poultry. This drug is poorly soluble in water, therefore, administration in drinking water may lead to high variability of concentrations in treated individuals. The use of injection preparations, however, requires individual administration and may have a negative effect on the quality of the carcass. In addition, the renal portal system in birds may reduce the bioavailability of the drug administered in the caudofemoral region of the body. The aim of this study was to compare the pharmacokinetics of florfenicol in turkeys after a single intravenous, intramuscular, and subcutaneous administration at a dose of 15 mg/kg body weight. Additionally, to evaluate the effect of renal portal system on drug kinetics, the intramuscular administration was divided into pectoral and caudofemoral administration. The study showed that the area under the concentration-time curve (AUC) was similar regardless of the route of administration. The mean values for clearance and volume of distribution were 0.33 L/kg/h and 0.92 L/kg, respectively. The mean residence time (MRT) was 2.87 h for an intravenous bolus, while for the extravascular administrations it was approx. 5.5 h. The elimination half-life was approx. 4 h regardless of the route of administration. The maximum plasma concentration did not differ statistically between intramuscular (approx. 6.8 mg/L) and subcutaneous (8.2 mg/L) administrations, while the time to appear for this concentration was the longest for caudofemoral administration (1.5 h). The bioavailability was 88.64% for subcutaneous administration, 77.95% for pectoral administration and 85.30% for caudofemoral administration. Overall, all 3 routes of extravascular administration allowed for efficient drug absorption. There was no evidence of an influence of the renal portal system on the kinetic parameters of the drug administered to the lower extremities of the body.

Assigning Defined Daily/Course Doses for Antimicrobials in Turkeys to Enable a Cross-Country Quantification and Comparison of Antimicrobial Use

Antimicrobial resistance (AMR) threatens our public health and is mainly driven by antimicrobial usage (AMU). For this reason the World Health Organization calls for detailed monitoring of AMU over all animal sectors involved. Therefore, we aimed to quantify AMU on turkey farms. First, turkey-specific Defined Daily Dose (DDD_turkey) was determined. These were compared to the broiler alternative from the European Surveillance of Veterinary Antimicrobial Consumption (DDD_vet), that mention DDD_vet as a proxy for other poultry species. DDD_turkey ranged from being 81.5% smaller to 48.5% larger compared to its DDD_vet alternative for broilers. Second, antimicrobial treatments were registered on 60 turkey farms divided over France, Germany and Spain between 2014 and 2016 (20 flocks per country). Afterwards, AMU was quantified using treatment incidence (TI) per 100 days. TI expresses the percentage of the rearing period that the turkeys were treated with a standard dose of antimicrobials. Minimum, median and maximum TI at flock level and based on DDD_turkey = 0.0, 10.0 and 65.7, respectively. Yet, a huge variation in amounts of antimicrobials used at flock level was observed, both within and between countries. Seven farms (12%) did not use any antimicrobials. Aminopenicillins, polymyxins, and fluoroquinolones were responsible for 72.2% of total AMU. The proportion of treating farms peaked on week five of the production cycle (41.7%), and 79.4% of the total AMU was administered in the first half of production. To conclude, not all DDD_vet values for broilers can be applied to turkeys. Additionally, the results of AMU show potential for reducing and improving AMU on turkey farms, especially concerning the usage of critically important antimicrobials.

Thermodynamic and Structural Powder Diffraction Studies of the Polymorphism of Florfenicol

Florfenicol is an antimicrobial drug used in veterinary medicine and aquaculture. Two polymorphic forms called A and B have been reported in literature, but the relation between these two forms are unknown. In order to get a better understanding of the behavior of solid florfenicol and the possible evolution from a metastable form to a stable one, an accurate thermodynamic study has been carried out by calorimetric measurements. For this purpose, temperatures and enthalpies of transition and of fusion of the stable and metastable forms have been measured by DSC. TGA has been used in view to detect the eventual existence of solvates which does not occur. In view to confirm the kind of transition, c_p measurements of the two forms have been performed with a C80 calorimeter. With these c_p values, it has been possible to determine the function of the variation of enthalpies as a function of temperature, ΔH = f (T). A study of the kinetic of transformation has been realized and is presented as well as the patterns of the X-ray powder diffraction from 295 to 426 K. This last approach confirms the crystal structure of form A of florfenicol previously reported in literature.

Comparative muscle irritation and pharmacokinetics of florfenicol-hydroxypropyl-β-cyclodextrin inclusion complex freeze-dried powder injection and florfenicol commercial injection in beagle dogs

Florfenicol (FF) is a novel animal-specific amidohydrin broad-spectrum antibiotic. However, its aqueous solubility is extremely poor, far below the effective dose required for veterinary clinic. Thus, FF is often used in large doses, which significantly limits its preparation and application. To overcome these shortcomings, the FF-hydroxypropyl-β-cyclodextrin (FF-HP-β-CD) inclusion complexes were developed using the solution-stirring method. The physical properties of FF-HP-β-CD were characterized. A comparison was conducted between FF and FF-HP-β-CD freeze-dried powder injection of their muscle irritation and the pharmacokinetics. The drug loading and saturated solubility of FF-HP-β-CD at 37 °C were 11.78% ± 0.04% and 78.93 ± 0.42 mg/mL, respectively (35.4-fold compared with FF). Results of scanning electron microscopy, differential scanning calorimetry, X-ray diffraction, and Fourier transform infrared showed that FF was entrapped in the inner cavity of HP-β-CD, and the inclusion complex formed in an amorphous state. In comparison with FF commercial injection, FF-HP-β-CD increased the elimination half-life (t_1/2β), transport rate constant (K₁₀, K₁₂, K₂₁), and maximum concentration (C_max) after intramuscular injection in beagle dogs. Conversely, it decreased the distribution half-life (t_1/2α), absorption rate constant (Ka), apparent volume of distribution (V1/F), and peak time (T_max). These results suggest that FF-HP-β-CD freeze-dried powder injection is a promising formulation for clinical application.

Comparative pharmacokinetics of florfenicol in healthy and Pasteurella multocida-infected Gaoyou ducks

Pasteurella multocida is the causative agent of fowl cholera, and florfenicol (FF) has potent antibacterial activity against P. multocida and is widely used in the poultry industry. In this study, we established a P. multocida infection model in ducks and studied the pharmacokinetics of FF in serum and lung tissues after oral administration of 30 mg/kg bodyweight. The maximum concentrations reached (C_max) were lower in infected ducks (13.88 ± 2.70 μg/ml) vs. healthy control animals (17.86 ± 1.57 μg/ml). In contrast, the mean residence time (MRT: 2.35 ± 0.13 vs. 2.27 ± 0.18 hr) and elimination half-life (T_½β : 1.63 ± 0.08 vs. 1.57 ± 0.12 hr) were similar for healthy and diseased animals, respectively. As a result, the area under the concentration curve for 0-12 hr (AUC_0-12 hr ) for FF in healthy ducks was significantly greater than that in infected ducks (49.47 ± 5.31 vs. 34.52 ± 8.29 μg hr/ml). The pharmacokinetic differences of FF in lung tissues between the two groups correlated with the serum pharmacokinetic differences. The C_max and AUC_0-12 hr values of lung tissue in healthy ducks were higher than those in diseased ducks. The concentration of FF in lung tissues was approximately 1.2-fold higher than that in serum both in infected and healthy ducks indicating that FF is effective in treating respiratory tract infections in ducks.