Influence of Escherichia coli lipopolysaccharide-induced endotoxemia on plasma and tissue disposition of florfenicol after intramuscular administration in rabbits.

To assess the effects of the acute inflammatory response (AIR) induced by Escherichia coli lipopolysaccharide (LPS) on plasma and tissue disposition of florfenicol (FFC) and its metabolite florfenicol amine (FFC-a), after its intramuscular (IM) administration, twenty-two New Zealand rabbits were randomly distributed in two experimental groups: Group 1 (LPS) was treated with three intravenous doses of 2 µg LPS/kg bw, before an intramuscular dose of 20 mg/kg FFC twenty-four h after the first LPS or SS injection; Group 2 (Control) was treated with saline solution (SS) in equivalent volumes as LPS-treated group. Blood samples were collected before (T0) and at different times after FFC administration. Acute inflammatory response was assessed in a parallel study where significant increases in body temperature, C-reactive protein concentrations and leukopenia were observed in the group treated with LPS. In another two groups of rabbits, 4 h after FFC treatment, rabbits were euthanized and tissue samples were collected for analysis of FFC and FFC-a concentrations. Pharmacokinetic parameters of FFC that showed significantly higher values in LPS-treated rabbits compared with control rabbits were absorption half-life, area under the curve, mean residence time and clearance /F (Cl/F). Elimination half-life and mean residence time of FFC-a were significantly higher in LPS-treated rabbits, whereas the metabolite ratio of FFC-a decreased significantly. Significant differences in tissue distribution of FFC and FFC-a were observed in rabbits treated with LPS. Modifications in plasma and tissue disposition of FFC and FFC-a were attributed mainly to haemodynamic modifications induced by the AIR through LPS administration.

Florfenicol urinary excretion and its potential for treating canine urinary tract infections.

The canine urinary excretion of florfenicol was evaluated to explore its potential for treating urinary tract infections. Nine healthy male intact purpose-bred Beagles and four healthy client-owned dogs each received a single oral dose of florfenicol 20 mg/kg (300 mg/mL parenteral solution) with food. All voluntary urinations were collected for 12 h. Although florfenicol is reportedly bitter tasting, 7/9 Beagles and 4/4 client-owned dogs completely ingested the florfenicol and were enrolled; salivation (n = 1) and headshaking (n = 3) were observed. The last measured urine florfenicol concentrations were variable: Beagles (0.23-3.19 mcg/mL), Pug (3.01 mcg/mL) English Setter (21.29 mcg/mL), Greyhound (32.68 mcg/mL), and Standard Poodle (13.00 mcg/mL). Urine half-life was similar for the Beagles and the Pug, 0.75-1.39 h, whereas the half-life was 1.70-1.82 h for the English Setter, Greyhound, and Standard Poodle. Larger breed dogs exceeded 8 mcg/mL florfenicol (wild-type cutoff) in their urine at 12 h, whereas the Beagles and Pug had <8 mcg/mL; it is unclear if this is an individual, breed, or size difference. These data suggest oral florfenicol may need to be administered q6-12h for canine urinary tract infections, but further data are needed (more enrolled dogs, multiple-dose regimens) before considering clinical trials or breed-specific differences.

Plasma disposition of florfenicol after intramuscular administration in rabbits pretreated with pentoxifylline.

This work aimed to assess the effects of the coadministration of pentoxifylline (PTX) on the pharmacokinetic profile of florfenicol (FFC) after intramuscular administration in rabbits. Ten New Zealand white rabbits, 1 year of age and 3.9 ± 0.1 kg body weight, were assigned according to a randomized block design to Group 1 (FFC): treated with 30 mg/kg of FFC intramuscularly, and Group 2 (PTX + FFC) treated with an oral dose of 30 mg/kg PTX 45 min before the intramuscular injection of 30 mg/kg FFC. Blood samples were collected before and at different times between 0.5 and 12.0 h after drug administration. FFC plasma concentrations were determined by high-performance liquid chromatography. Results showed that IM injection of the long-acting formulation of FFC in rabbits resulted in a slow increase in mean plasma concentrations reaching a Cmax of 3.09 ± 0.52 ug/mL at 2.8 ± 0.45 h (Tmax ) after drug administration. While coadministration of PTX and FFC decreased the time to achieve the maximal concentration by modifying the absorption of FFC without changes in the other pharmacokinetic parameters.

Comparative pharmacokinetics of florfenicol in heifers after intramuscular and subcutaneous administration.

Florfenicol was administered to five heifers intramuscularly at a dose rate of 20 mg/kg bwt and following wash-out period, subcutaneously at a dose rate of 40 mg/kg bwt. Blood plasma samples were collected from heifers before injection of florfenicol and up to 120 h after intramuscular (IM) injection and up to 264 h after subcutaneous (SC) injection. Florfenicol concentrations in plasma were measured by high-performance liquid chromatography with mass-spectrometric detection. Pharmacokinetics of florfenicol was estimated using non-compartment analysis. Mean maximum plasma concentration, area under the concentration-time curve and elimination half-life for florfenicol were 3.2 µg/ml, 101.5 µg × h/ml and 24.5 h, respectively, after IM injection at 20 mg/kg bwt, and 2.7 µg/ml, 194.5 µg × h/ml and 103.8 h, respectively, after SC injection at 40 mg/kg bwt. The obtained results indicated that both administration routes provided comparable bioavailability, whereas SC route was attributed with lower peak levels and markedly slower absorption of florfenicol from injection site. Both administration routes provided plasma florfenicol levels which are expected to be effective against prevalent infectious agents of cattle.

Effects of starvation on the pharmacokinetics and optimal dosages of florfenicol and associated serum biochemistry in Asian seabass (Lates calcarifer).

Starvation has influence on physiology and pharmacokinetic (PK) characteristics of many drugs in land animals. However, similar PK information in fish is lacking. The current study examined the effects of starvation on fish PK, taking florfenicol (FF) in Asian seabass as an example. FF was orally administered at a single dose of 10 mg/kg into 35-day starved fish reared at 25 and 30°C and the serum FF concentration was analyzed by HPLC-FLD. At 30°C, the absorption and elimination half-lives of the starved fish were increased by 30% (from 0.44 to 0.57 h) and 55% (from 7.2 to 11.18 h), respectively. The volume of distribution, clearance, and area under the curve were changed from 1.25 to 0.71 L/kg, 0.120 to 0.044 L/kg/h, and 88 to 228 h·µg/ml, respectively. Similar starvation-induced PK changes were also observed at 25°C. The serum biochemical parameters, mainly the alanine aminotransferase, aspartate aminotransferase, and glucose levels, were significantly reduced in the starvation group. Overall, FF absorption, distribution, and elimination rates were reduced by starvation, resulting in four to five times lower optimal dosage than the non-starved fish. Drug treatment in starved fish should be treated with caution as overdosing and/or tissue residues could perceivably occur.

Differential effects of aquatic anaesthetics on the pharmacokinetics of antibiotics: Examples using florfenicol in Nile tilapia (Oreochromis niloticus).

Anaesthetics are commonly applied in pharmacokinetic (PK) studies to assure smooth handling of experimental procedures or to promote animal welfare. However, the influence of anaesthetics on the PK of co-administered drug is generally unknown but assumes ignorable. The goal of the study was to investigate the effect of tricaine methanesulfonate (MS-222), 2-phenoxyethanol (2-PE) and eugenol (EUG) on the PK of florfenicol (FF) in Nile tilapia. Twenty-eight fish were repeatedly exposed to 90 ppm EUG, 300 ppm MS-222 or 900 ppm 2-PE before FF oral administration (15 mg/kg) and each successive blood sampling. The serum concentration-time profiles were analysed by a 2-compartmental model, and the generated parameters in the control (without anaesthetic) and anaesthetic groups were statistically compared. The results demonstrated that the serum concentrations of each anaesthetic were similar at every FF sampling times (70 µg/ml for MS-222; 277 µg/ml for 2-PE; and 61 µg/ml for EUG). In comparison with the control group, the repeated use of MS-222 did not result in a statistical difference in most of the PK parameters. In contrast, the elimination half-lives of the 2-PE and EUG groups were significantly longer whereas the absorption and distribution half-lives of the 2-PE group were significantly shorter than the control, resulting in altered optimal dosages in the simulation modelling. Whether or not the numbers and extent of PK parameters change mitigate subsequent estimations of other PK-derived secondary values such as dosing regimen and withdrawal time remains to be elucidated, but the auxiliary use of anaesthetics in PK studies should not assume uninfluential.

Modelagem farmacocinética/farmacodinâmica do florfenicol para o tratamento da adenite equina por meio da simulação de Monte Carlo / Pharmacokinetic/pharmacodynamic modeling of florfenicol for the treatment of equine adenitis using Monte Carlo simulation

O objetivo deste trabalho foi avaliar a eficácia do florfenicol na dose usualmente empregada em equinos de 22 mg/kg pelas vias intravenosa, intramuscular e oral para o tratamento de adenite equina por Streptococcus equi. subsp. equi, usando a modelagem farmacocinética/farmacodinâmica (PK/PD – Pharmacokinetic/Pharmacodynamic) e a simulação de Monte Carlo. Foi realizada uma simulação de Monte Carlo a partir dos parâmetros PK, logo depois, efetuou-se a modelagem PK/PD para determinar as taxas de eficácia do antimicrobiano para o tratamento dessa infecção bacteriana, de acordo com o valor da concentração inibitória mínima (CIM), em um intervalo de CIM de 0,125 – 4 μg/mL. Pela via intravenosa, a probabilidade de erradicação bacteriana foi de 100% para CIM até 0,5 μg/mL e efeito bacteriostático com probabilidades de 99% e 80% para CIMs de 2 e 4 μg/mL, respectivamente. Já pelas vias intramuscular e oral a probabilidade de se atingir o índice de erradicação bacteriológica foi de 100% para CIM de até 0,5 μg/mL, contudo, atinge valores de 80% e 81%, respectivamente, para CIM de 1 μg/mL considerando o efeito bactericida (p<0,01). Portanto, através desse estudo é evidenciado a eficácia do florfenicol até a CIM de 0,5 μg/mL para as três vias de administração citadas, entretanto, para CIMs superiores a esse valor, é imprescindível o ajuste da dose farmacológica, evitando falhas na terapêutica e possível resistência microbiana.

The objective of this study was to evaluate the efficacy of florfenicol at the dose usually used in horses of 22 mg/kg by intravenous, intramuscular and oral routes for the treatment of equine adenitis caused by Streptococcus equi. subsp. equi, using Pharmacokinetic/Pharmacodynamic (PK/PD) modeling and Monte Carlo simulation. A Monte Carlo simulation was performed from the PK parameters, then PK/PD modeling was performed to determine the antimicrobial efficacy rates for the treatment of this bacterial infection, according to the minimum inhibitory concentration (MIC) value, in a MIC range of 0.125 - 4 μg/mL. Intravenously, the probability of bacterial eradication was 100% for MICs up to 0.5 μg/mL, and the bacteriostatic effect was 99% and 80% for MICs of 2 and 4 μg/mL, respectively. However, for the intramuscular and oral routes, the probability of reaching the bacteriologic eradication index was 100% for MICs of up to 0.5 μg/mL, however, it reaches values of 80% and 81%, respectively, for MICs of 1 μg/mL considering the bactericidal effect (p<0.01). Therefore, through this study the efficacy of florfenicol is evidenced up to the MIC of 0.5 μg/mL for the three routes of administration cited, however, for MICs higher than this value, it is essential to adjust the pharmacological dose, avoiding failures in therapy and possible microbial resistance.

Bayesian population physiologically-based pharmacokinetic model for robustness evaluation of withdrawal time in tilapia aquaculture administrated to florfenicol.

The antimicrobial residues of aquacultural production is a growing public concern, leading to reexamine the method for establishing robust withdrawal time and ensuring food safety. Our study aims to develop the optimizing population physiologically-based pharmacokinetic (PBPK) model for assessing florfenicol residues in the tilapia tissues, and for evaluating the robustness of the withdrawal time (WT). Fitting with published pharmacokinetic profiles that experimented under temperatures of 22 and 28 °C, a PBPK model was constructed by applying with the Bayesian Markov chain Monte Carol (MCMC) algorithm to estimate WTs under different physiological, environmental and dosing scenarios. Results show that the MCMC algorithm improves the estimates of uncertainty and variability of PBPK-related parameters, and optimizes the simulation of the PBPK model. It is noteworthy that posterior sets generated from temperature-associated datasets to be respectively used for simulating residues under corresponding temperature conditions. Simulating the residues under regulated regimen and overdosing scenarios for Taiwan, the estimated WTs were 12-16 days at 22 °C and 9-12 days at 28 °C, while for the USA, the estimated WTs were 14-18 and 11-14 days, respectively. Comparison with the regulated WT of 15 days, results indicate that the current WT has well robustness and resilience in the environment of higher temperatures. The optimal Bayesian population PBPK model provides effective analysis for determining WTs under scenario-specific conditions. It is a new insight into the increasing body of literature on developing the Bayesian-PBPK model and has practical implications for improving the regulation of food safety.

Evaluation of absorption and depletion of florfenicol in European seabass Dicentrarchus labrax.

The pharmacokinetic properties and residue elimination of florfenicol (FLO) and its amine were investigated in European seabass Dicentrarchus labrax at 24°C. The trial mainly included analysis of FLO in plasma after a single dose dietary administration of 10 mg/kg and in muscle plus skin following a multiple dosing (10 mg kg-1  day-1 for 7 days) to estimate pharmacokinetics and residue depletion, respectively. The maximum plasma concentration of FLO was measured to be 1.64 µg/ml, 4 hr post administration. The elimination half-life (t1/2b ) and the area under the concentration-time curve extrapolated to infinity (AUC0-∞ ) were calculated to be 13.0 hr and 34.7 µg h-1  ml-1 , respectively. Withdrawal times of FLO and its amine were calculated to be 46.3 degree-days, indicating a fast removal from the edible tissues of treated European seabass. Overall, FLO can be considered as a potentially efficient antibacterial agent for farmed European seabass provided that additional efforts will be devoted towards its in vitro and clinical efficacy.

Pharmacokinetics of thiamphenicol in Japanese quails (Coturnix japonica) after single intravenous and oral administrations.

Thiamphenicol (TP) pharmacokinetics were studied in Japanese quails (Coturnix japonica) following a single intravenous (IV) and oral (PO) administration at 30 mg/kg BW. Concentrations of TP were determined with HPLC and were analyzed by a noncompartmental method. After IV injection, elimination half-life (t1/2λz ), total body clearance (Cltot ) volume of distribution at steady state (Vdss ), and mean residence time (MRT) of TP were 3.83 hr, 0.19 L/hr/kg, 0.84 L/kg, and 4.37 hr, respectively. After oral administration of TP, the peak plasma concentration (Cmax ) was 19.81 µg/ml and was obtained at 2.00 hr (tmax ) postadministration. Elimination half-life (t1/2λz ) and mean absorption time (MAT) were 4.01 hr and 1.56 hr, respectively. The systemic bioavailability following oral administration of TP was 78.10%. TP therapy with an oral dosage of 30 mg/kg BW is suggested for a beneficial clinical effect in quails.

Bath immersion pharmacokinetics of florfenicol in Nile tilapia (Oreochromis niloticus).

Drug administration by immersion can be a preferable method in certain conditions especially for treating small-sized, anorexic, or valuable fish. Pharmacokinetic information regarding bath treatment is considerably lacking in comparison to other common administration routes. The current study aimed to investigate if immersion can be an effective route to administer florfenicol (FF) for treatment in Nile tilapia. Nile tilapia reared at 28°C were immersed with FF solution at concentrations of 50, 100, 200, 500, and 500/200 (3 hr/117 hr) ppm for 120 hr and moved to drug-free freshwater for another 24 hr. The serum FF concentration in 100, 200, and 500/200 ppm groups reached steady-state at 12 hr with concentrations of 2.44, 3.04, and 5.26 µg/ml, respectively, which were about 2% of the bathing concentrations. The target therapeutic levels of 1-4 µg/ml were attained and maintained within 1-12 hr, depending on the immersion concentration and the target MIC. Serum FF reached the target with shorter time at higher bathing concentration. Following the 120-hr bath, the serum FF declined with the first-order half-life of approximately 10 hr. A minimum of 100 ppm FF is required for treatment purpose, and an initial high loading concentration followed by maintenance concentration is a plausible way to reach in vivo therapeutic level in short time. Greater than 99% of the residual FF in the bathing water could be removed within 15 min by 0.05% NaOCl. Our results indicated that bath immersion is a promising potential route for FF administration in Nile tilapia.

Poloxamer modified florfenicol instant microparticles for improved oral bioavailability.

Surfactants can improve the hydrophobicity of poorly water-soluble drugs and increase the stability of microparticles by reducing surface tension. This study describes that surfactant-engineered florfenicol instant microparticles (FIMs) increase bioavailability through a micellar solubilization mechanism. The FIMs were prepared by a modified emulsification method, and the optimal prescription was obtained by a combination of single factor investigation and response surface methodology. The microparticles prepared in this study reduce the polymer materials while increasing the drug content. FIM has a smaller particle size and modification of poloxamer, resulting in better solubility and higher bioavailability. The in vitro solubility of FIM is 1.43 times higher than that of the bulk drug, and the dissolution equilibrium can be achieved in 10 minutes. Compared with florfenicol, FIM showed a decrease in Tmax in the plasma concentration curve, with a peak concentration of 1.43 times and an area of 1.41 times. Considering the advantages of in vitro/in vivo performance and ease of preparation, FIMs may have great application prospects in pharmacy research.

Effects of the dietary inclusion of a probiotic or prebiotic on florfenicol pharmacokinetic profile in broiler chicken.

We evaluated the effect of prebiotic or probiotic as feed additives on florfenicol kinetic in broilers feed. Unsexed two hundred, thirty-five-day-old broiler chickens, were put in four equal groups (n = 50). The first group was administrated florfenicol intravenous at 30 mg/kg body weight (BW) only once dosage without pre- or probiotic administration to determine the bioavailability. While, the second group was administrated florfenicol (intracrop routes; a dosage of 30 mg/kg BW for five progressive days) without pre- or probiotic co-administration. The third and the fourth groups were administrated the same dose of florfenicol (intracrop route) for five successive days, followed by 10 days of prebiotic or probiotic treatment respectively. The plasma florfenicol % was identified by high-pressure liquid chromatography (HPLC) after the first florfenicol administration (intravenous or intracrop routes) in all groups. Then, the residual levels of florfenicol were determined in liver, kidney and muscle tissues from the second, third and fourth groups which were exposed to florfenicol orally. Our results demonstrated that broilers pre-treated with prebiotic or probiotic significantly increased Cmax , AUC0- t , AUC0-inf as well as AUMC values, while significant drop was recorded in V/F and CL/F. Prebiotic or probiotic influenced the cumulative effect of florfenicol in liver and kidney tissues of treated birds.

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.

Increased bioaffinity and anti-inflammatory activity of florfenicol nanocrystals by wet grinding method.

Context: The main objective of the current study is to improve the water solubility of florfenicol (FF) and evaluate changes in its pharmacokinetics and anti-inflammatory activity.Materials and methods: Florfenicol nanocrystals (FF-NC) were prepared by wet grinding combined with spray drying. The characterisations, pharmacokinetics, and anti-inflammatory activity of FF-NC were evaluated.Results: The particle size, polydispersity index (PDI), and zeta potential of FF-NC were 276.4 ± 19.4 nm, 0.166 ± 0.011, and -18.66 ± 5.25 mV, respectively. Compared with FF, FF-NC showed a better dissolution rate in media at different pH. Pharmacokinetic experiments showed the area under the curve (AUC0-t), maximum concentration (Cmax), and mean residence time (MRT) of FF-NC were about 4.62-fold, 2.86-fold, and 1.68-fold higher compared with FF, respectively. In vitro anti-inflammatory experiments showed that FF inhibited the secretion of tumour necrosis factor-α (TNF-α), interleukin-6 (IL-6), and synthesis of NO in a dose-dependent manner, while FF-NC showed a stronger anti-inflammatory effect than FF under the same dose.Conclusion: FF-NC are an effective way to improve the bioaffinity and anti-inflammatory effects of FF.

Comparative muscle irritation and pharmacokinetics of florfenicol-hydroxypropyl-ß-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-ß-cyclodextrin (FF-HP-ß-CD) inclusion complexes were developed using the solution-stirring method. The physical properties of FF-HP-ß-CD were characterized. A comparison was conducted between FF and FF-HP-ß-CD freeze-dried powder injection of their muscle irritation and the pharmacokinetics. The drug loading and saturated solubility of FF-HP-ß-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-ß-CD, and the inclusion complex formed in an amorphous state. In comparison with FF commercial injection, FF-HP-ß-CD increased the elimination half-life (t1/2ß), transport rate constant (K10, K12, K21), and maximum concentration (Cmax) after intramuscular injection in beagle dogs. Conversely, it decreased the distribution half-life (t1/2α), absorption rate constant (Ka), apparent volume of distribution (V1/F), and peak time (Tmax). These results suggest that FF-HP-ß-CD freeze-dried powder injection is a promising formulation for clinical application.

Effects of anemoside B4 on pharmacokinetics of florfenicol and mRNA expression of CXR, MDR1, CYP3A37 and UGT1E in broilers.

Pulsatillae radix, a traditional Chinese medicine (TCM), is often used in combination with florfenicol for treatment of intestinal infection in Chinese veterinary clinics. Anemoside B4 (AB4) is the major effective saponin in Pulsatillae radix. This study aimed to investigate whether the pharmacokinetics of florfenicol in broilers was affected by the combination of AB4. In this study, broilers were given AB4 (50 mg/kg BW), or 0.9% sodium chloride solution by oral administration for 7 days. They were then fed florfenicol orally (30 mg/kg BW) on the eighth day. The results showed that the AUC(0-∞), MRT(0-∞), t1/2z and Cmax of florfenicol were significantly decreased, and the Vz/F and CLz/F were significantly increased by AB4; the mRNA expression levels of CXR, CYP3A37 and MDR1 (except CXR and CYP3A37 in the liver) were up-regulated by AB4. In conclusion, AB4 altered the pharmacokinetics of florfenicol, resulting in lower plasma concentrations of florfenicol, this was probably related to the mRNA expression of CXR, CYP3A37 and MDR1 in the jejunum and liver (except CXR and CYP3A37) increased by AB4. The implications of these findings on the effect of traditional Chinese medicine containing AB4 on the effectiveness of florfenicol in veterinary practice deserve study.

Pharmacokinetics of florfenicol in blunt-snout bream (Megalobrama amblycephala) at two water temperatures with single-dose oral administration.

The pharmacokinetics and residue elimination of florfenicol (FFC) and its metabolite florfenicol amine (FFA) were studied in healthy blunt-snout bream (Megalobrama amblycephala, 50 ± 10 g). The study was conducted with a single-dose (25 mg/kg) oral administration at a water temperature of 18 or 28°C, while in the residue elimination study, fish were administered at 25 mg/kg daily for three consecutive days by oral gavage to determine the withdrawal period (WDT) at 28°C. The FFC and FFA levels in plasma and tissues (liver, kidneys and muscle) were analysed using high-performance liquid chromatography (HPLC). A no-compartment model was used to analyse the concentration versus time data of M. amblycephala. In the two groups at 18 and 28°C, the maximum plasma concentration (Cmax ) of FFC was 5.89 and 6.21 µg/ml, while the time to reach Cmax (Tmax ) was 5.97 and 2.84 hr, respectively. These suggested that higher temperature absorbed more drug and more quickly at M. amblycephala. And the elimination half-life (T1/2 kß ) of FFC was calculated as 26.75 and 16.14 hr, while the total body clearance (CL) was 0.09 and 0.15 L kg-1  hr-1 , and the areas under the concentration-time curves (AUCs) were 265.87 and 163.31 µg hr/ml, respectively. The difference demonstrated that the elimination rate of FFC in M. amblycephala at 28°C was more quickly than that at 18°C. The results of FFA showed the same trend in tissues of M. amblycephala. After multiple oral doses (25 mg/kg daily for 3 days), the k (eliminate rate constant) of FFA in M. amblycephala muscle was 0.017, the C0 (initial concentration) was 3.07 mg/kg, and the WDT was 10 days (water temperature 28°C).

Pharmacokinetic-pharmacodynamic modelling for the determination of optimal dosing regimen of florfenicol in Nile tilapia (Oreochromis niloticus) at different water temperatures and antimicrobial susceptibility levels.

Optimized dosing regimen is key to the effective use of antibacterials and to minimizing drug-related side effects. The current study established a pharmacokinetic-pharmacodynamic (PK-PD) model for the determination of optimal antibacterial dosing regimen in fish taken into consideration the temperature-dependent PK and the pathogen-dependent antimicrobial susceptibility, using florfenicol (FF) in Nile tilapia as an example. The calculated optimal dosages significantly varied by temperature and target MIC levels, ranging from 2.23 (MIC 1 µg/ml at 24°C) to 34.88 mg kg-1  day-1 (MIC 4 µg/ml at 32°C). The appropriateness of the calculated dosages was successfully verified by the in vivo studies. After 5 days of oral administration of the calculated optimal dosage at 24°C, the predicted plasma drug values were in line with the mean observed Cmin(ss) while at 28 and 32°C underestimation of the Cmin(ss) in a dose-dependent manner was observed and likely due to the occurrence of non-linear PK at high dosages. The averaged serum protein binding of FF was 19.1%. Our results demonstrated the appropriateness and clinical applicability of the developed PK-PD approach for the determination of optimal dosing regimens at given temperatures and MICs. Saturation metabolism and PK non-linearity of FF in tilapia warrant further study.

Development and Characterization of Florfenicol-Loaded BSA Nanoparticles as Controlled Release Carrier.

Florfenicol (FLO) is a broad-spectrum fluorinated antibiotic used for the treatment of bacterial diseases such as bovine respiratory disease (BRD) in cattle. FLO is a poorly soluble drug in aqueous solution, and its encapsulation in various nanovehicles has been reported to be less than 30%. In this context, the use of bovine serum albumin (BSA) as a nanocarrier for FLO is an interesting approach. BSA is a biocompatible, biodegradable, nontoxic, and nonimmunogenic natural protein, allowing the vehiculization of hydrophilic and hydrophobic drugs with a well-tolerated administration. The present work focuses on the fabrication and characterization of florfenicol-loaded BSA (FLO-BSA NPs), incorporation efficiency, and in vitro release pattern. FLO-BSA NPs nanoparticles were successfully obtained by a simple, low-cost and in a few steps method. The physicochemical properties of the obtained nanoparticles such as size (~ 120 nm), polydispersity index (0.04), and zeta potential (approximately - 40 mV) suggest a high colloidal stability and suitable characteristics for drug delivery. The drug loading reveals a high incorporation of florfenicol in the nanoparticles, in which 33.6 molecules of FLO are encapsulated per each molecule of BSA. The in vitro release profile exhibits an initial stage characterized by the burst effect and then a prolonged release of FLO from the albumin matrix, which is compatible with the Higuchi model and which follows a Fickian diffusion. The results together suggest a suitable tool for future investigations in drug delivery field in order to use this nanomaterial in food, pharmaceutical, and veterinary industry.