Efficacy of florfenicol on experimental Actinobacillus pleuropneumonia in pigs

A Green HPLC Approach to Florfenicol Analysis in Pig Urine

Florfenicol (FF) is a broad-spectrum antibiotic used to treat gastrointestinal and respiratory infections in domestic animals. Considering FF's rapid elimination via urine after drug treatment, its use increases concerns about environmental contamination. The objective of the study was to establish a sustainable chromatographic method for simple analysis of FF in pig urine to investigate the urinary excretion of FF after a single intramuscular administration of 20 mg FF/kg body weight. The urine sample was prepared using a centrifuge and regenerated cellulose filter, and the diluted sample was analyzed. The method was validated in terms of linearity, the limit of detection (0.005 µg/mL) and quantitation (0.016 µg/mL), repeatability and matrix effect (%RSD ranged up to 2.5), accuracy (varied between 98% and 102%), and stability. The concentration-time profile of pig urine samples collected within 48 h post-drug administration showed that 63% of FF's dose was excreted. The developed method and previously published methods used to qualify FF in the urine of animal origin were evaluated by the National Environmental Method Index (NEMI), Green Analytical Procedure Index (GAPI) and Analytical GREENness Metric Approach (AGREE). The greenness profiles of published methods revealed problems with high solvents and energy consumption, while the established method was shown to be more environmentally friendly.

Pharmacokinetics and Pharmacodynamics of Florfenicol in Plasma and Synovial Fluid of Pigs at a Dose of 30 mg/kgbw Following Intramuscular Administration

A major problem of our time is the ever-increasing resistance to antimicrobial agents in bacterial populations. One of the most effective ways to prevent these problems is to target antibacterial therapies for specific diseases. In this study, we investigated the in vitro effectiveness of florfenicol against S. suis, which can cause severe arthritis and septicemia in swine herds. The pharmacokinetic and pharmacodynamic properties of florfenicol in porcine plasma and synovial fluid were determined. After a single intramuscular administration of florfenicol at 30 mg/kg_bw, the AUC_0-∞ was 164.45 ± 34.18 µg/mL × h and the maximum plasma concentration was 8.15 ± 3.11 µg/mL, which was reached in 1.40 ± 0.66 h, whereas, in the synovial fluid, these values were 64.57 ± 30.37 µg/mL × h, 4.51 ± 1.16 µg/mL and 1.75 ± 1.16 h, respectively. Based on the MIC values of the 73 S. suis isolates tested, the MIC₅₀ and MIC₉₀ values were 2 µg/mL and 8 µg/mL, respectively. We successfully implemented a killing-time curve in pig synovial fluid as a matrix. Based on our findings, the PK/PD breakpoints of the bacteriostatic (E = 0), bactericidal (E = -3) and eradication (E = -4) effects of florfenicol were determined and MIC thresholds were calculated, which are the guiding indicators for the treatment of these diseases. The AUC_24h/MIC values for bacteriostatic, bactericidal and eradication effects were 22.22 h, 76.88 h and 141.74 h, respectively, in synovial fluid, and 22.42 h, 86.49 h and 161.76 h, respectively, in plasma. The critical MIC values of florfenicol against S. suis regarding bacteriostatic, bactericidal and eradication effects in pig synovial fluid were 2.91 ± 1.37 µg/mL, 0.84 ± 0.39 µg/mL and 0.46 ± 0.21 µg/mL, respectively. These values provide a basis for further studies on the use of florfenicol. Furthermore, our research highlights the importance of investigating the pharmacokinetic properties of antibacterial agents at the site of infection and the pharmacodynamic properties of these agents against different bacteria in different media.

Improving intestinal absorption and antibacterial effect of florfenicol via nanocrystallisation technology

To study the effects of nanocrystallisation technology on the intestinal absorption properties and antibacterial activity of florfenicol (FF). The florfenicol nanocrystals (FF-NC) were prepared by wet grinding and spray drying. Additionally, changes in particle size, charge, morphology, and dissolution of FF-NC in the long-term stability were monitored by laser particle sizer, TEM, SEM, paddle method, and the structure of FF-NC powder was characterised by nuclear magnetic resonance (NMR) test. The antibacterial activity, intestinal absorption and intestinal histocompatibility of FF-NC were investigated by the stiletto, mini broth dilution susceptibility test, in situ single-pass intestinal perfusion (SPIP) and haematoxylin-eosin (H-E) staining. After 12 months of storage, the particle size and zeta potential of FF-NC were 280.43 ± 8.21 nm and -19.64 ± 3.45 mV, and the electron microscopy results showed that FF-NC were nearly circular with no adhesion between particles. In addition, the drug loading, encapsulation efficiency, and dissolution of FF-NC did not change significantly during storage. The inhibition zone of FF-NC against Escherichia coli and Staphylococcus aureus was 21.37 ± 1.70 mm and 25.17 ± 2.47 mm, respectively. Compared with the FF, the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of FF-NC are reduced, and the absorption rate constant (K_a) and efficient permeability coefficient (P_eff) of FF-NC in the three intestinal segments were increased by 1.28, 0.25, and 9.10 times and 0.59, 0.17, and 6.0 times, respectively. The results of tissue sections showed that FF-NC had little damage to the small intestinal. Nanocrystallisation technology is an effective method to increase the intestinal absorption and antibacterial activity of FF.

Maximum levels of cross-contamination for 24 antimicrobial active substances in non-target feed. Part 7: Amphenicols: florfenicol and thiamphenicol

The specific concentrations of florfenicol and thiamphenicol in non-target feed for food-producing animals, below which there would not be an effect on the emergence of, and/or selection for, resistance in bacteria relevant for human and animal health, as well as the specific antimicrobial concentrations in feed which have an effect in terms of growth promotion/increased yield, were assessed by EFSA in collaboration with EMA. Details of the methodology used for this assessment, associated data gaps and uncertainties, are presented in a separate document. To address antimicrobial resistance, the Feed Antimicrobial Resistance Selection Concentration (FARSC) model developed specifically for the assessment was applied. The FARSC for florfenicol was estimated. However, due to the lack of data, the calculation of the FARSC for thiamphenicol was not possible until further experimental data become available. To address growth promotion, data from scientific publications obtained from an extensive literature review were used. Levels in feed that showed to have an effect on growth promotion/increased yield were reported for florfenicol, whilst for thiamphenicol no suitable data for the assessment were available. Uncertainties and data gaps associated to the levels reported were addressed. For florfenicol, it was recommended to perform further studies to supply more diverse and complete data related to the requirements for calculation of the FARSC, whereas for thiamphenicol, the recommendation was to generate the data required to fill the gaps which prevented the FARSC calculation.

Catalytic Syn-Selective Nitroaldol Approach to Amphenicol Antibiotics: Evolution of a Unified Asymmetric Synthesis of (-)-Chloramphenicol, (-)-Azidamphenicol, (+)-Thiamphenicol, and (+)-Florfenicol

A unified strategy for an efficient and high diastereo- and enantioselective synthesis of (-)-chloramphenicol, (-)-azidamphenicol, (+)-thiamphenicol, and (+)-florfenicol based on a key catalytic syn-selective Henry reaction is reported. The stereochemistry of the ligand-enabled copper(II)-catalyzed aryl aldehyde Henry reaction of nitroethanol was first explored to forge a challenging syn-2-amino-1,3-diol structure unit with vicinal stereocenters with excellent stereocontrol. Multistep continuous flow manipulations were carried out to achieve the efficient asymmetric synthesis of this family of amphenicol antibiotics.

Florfenicol induces renal toxicity in chicks by promoting oxidative stress and apoptosis

To explore the mechanism of renal toxicity induced by florfenicol (FFC), 120 chicks were randomly divided into 6 groups, 20 in each group. Except for the control group, different doses of FFC (0.15 g/L, 0.3 g/L, 0.6 g/L, 1.2 g/L, and 1.8 g/L) were added to drinking water in the other 5 groups. Five days later, blood was collected from the vein under the wing, and the complete kidneys were obtained as soon as possible, then tested the experimental indicators. The results showed that compared with control group, all doses of FFC significantly reduced the average weight gain of chicks (P < 0.05 or P < 0.01). Except for the 0.15 g/L FFC group, kidney index of chicks in the other doses of FFC groups were significantly increased (P < 0.05 or P < 0.01). The kidney tissues in all FFC groups showed obvious damage, deformities, cell atrophy, and cell gap enlargement. In addition, all doses of FFC significantly increased the contents of uric acid (UA), blood urea nitrogen (BUN), creatinine (CRE) in serum, and malondialdehyde (MDA) in renal tissue (P < 0.05 or P < 0.01), but significantly reduced the levels of glutathione (GSH), superoxide dismutase (SOD), and catalase (CAT) in renal tissue (P < 0.05 or P < 0.01). FFC significantly inhibited the mRNA and protein expression levels of nuclear factor-erythroid 2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1), and nicotinamide adenine dinucleotide phosphate: quinone oxidoreductase-1 (NQO-1), and increased the mRNA and protein expression levels of p53, Caspase-3, and Caspase-6 (P < 0.05 or P < 0.01). The apoptotic rate of renal cells in all doses of FFC groups increased significantly (P < 0.05 or P < 0.01). It was concluded that FFC had a certain degree of nephrotoxicity, and with the increase of FFC concentration, the kidney injury of chicks became more and more serious. FFC promoted oxidative stress response in kidney of chicks by inhibiting the expression of related factors in Nrf2-ARE pathway. Moreover, the expression of pro-apoptotic factors was upregulated to improve the apoptosis rate of renal cells, which resulted in excessive apoptosis of renal cells and seriously affected the kidney function of chicks.

Growth and cardiovascular development are repressed by florfenicol exposure in early chicken embryos

Florfenicol (FLO) is one of the most popular antibacterial drugs used in veterinary clinics and aquaculture. The drug was found to decrease the hatchability of eggs laid by treated hens in veterinary clinics and research work. However, the pathological changes in developing embryos and their cardiovascular system and the mechanism underlying FLO-induced embryonic death remain unclear. In the present study, fertilized eggs laid by hens treated with a therapeutic dose of FLO were collected and incubated. Results showed that FLO exposure repressed embryonic development and induced early embryonic death. As a result, FLO decreased the hatchability and increased the proportion of weak chicks. Moreover, FLO exposure led to embryonic lethality and inhibited the development of chick embryos as characterized by decreased weights, lagging distribution of Hamburger–Hamilton stages, and dysplastic eyes. Pathological examination indicated that FLO exposure affected the normal development of the heart in 4.5-day-old chick embryos, as characterized by shorter transverse cardiac diameter, disordered arrangement of trabecular muscles in ventricles, and reduced thickness of ventricular walls. Furthermore, FLO decreased blood vascular densities and downregulated the expression levels of key angiogenesis-related genes, including the vascular endothelial growth factor and fibroblast growth factor, in the yolk sac membrane. These findings indicated that FLO exposure restricted vascular development during early embryonic development. In summary, our data suggest that the restricted growth and abnormal cardiovascular development may be responsible for FLO-induced early embryonic death. Thus, these findings can be useful for guiding the proper use of FLO and in laying a foundation for further studies on the mechanism of FLO-induced embryonic toxicity.

The prevalence of amphenicol resistance in Escherichia coli isolated from pigs in mainland China from 2000 to 2018: A systematic review and meta-analysis

BACKGROUND

Amphenicols have been widely used in the pig industry in China, leading to varying degrees of drug resistance.

METHODS

The systematic review was performed according to PRISMA (Preferred Reported Items for Systematic Reviews and Meta-Analysis) recommendations on studies investigating the prevalence of amphenicol-resistant Escherichia coli (E. coli) isolated from pig in mainland China from 2000 to 2018, a random-effects model was selected, then followed by meta-analysis.

RESULTS

A total of 103 articles were included in the study. The results of the meta-analysis revealed that the pooled summarized prevalence of resistance to chloramphenicol (CAP) was 72.31% (95% confidence interval (95% CI) = 67.12%-77.23%) and to florfenicol (FF) was 58.64% (95% CI = 52.48%-64.67%). During the past 18 years, the resistance rate to CAP remained high initially but then declined rapidly after 2012, whereas the resistance rate to FF plateaued (54.13%-59.60%) from 2000-2018. In different parts of China, the rate of resistance to amphenicols among E. coli isolates was fairly consistent, with the exception of the north and northwest regions.

CONCLUSIONS

In 2002, the veterinary use of CAP was prohibited and its resistance levels in E. coli isolated from pigs was initially maintained at a high level but then showed an obvious downward trend in recent years. Resistance to commonly used FF remained at a high but stable level.

Resistant cutoff values and optimal scheme establishments for florfenicol against Escherichia coli with PK-PD modeling analysis in pigs

Florfenicol, a structural analog of thiamphenicol, has broad-spectrum antibacterial activity against gram-negative and gram-positive bacteria. This study was conducted to investigate the epidemiological, pharmacokinetic-pharmacodynamic cutoff, and the optimal scheme of florfenicol against Escherichia coli (E. coli) with PK-PD integrated model in the target infectious tissue. 220 E. coli strains were selected to detect the susceptibility to florfenicol, and a virulent strain P190, whose minimum inhibitory concentration (MIC) was similar to the MIC₅₀ (8 μg/ml), was analyzed for PD study in LB and ileum fluid. The MIC of P190 in the ileum fluid was 0.25 times lower than LB. The ratios of MBC/MIC were four both in the ileum and LB. The characteristics of time-killing curves also coincided with the MBC determination. The recommended dosages (30 mg/kg·body weight) were orally administrated in healthy pigs, and both plasma and ileum fluid were collected for PK study. The main pharmacokinetics (PK) parameters including AUC_24 hr , AUC_0-∞ , T_max , T_1/2 , C_max , CL_b, and K_e were 49.83, 52.33 μg*h/ml, 1.32, 10.58 hr, 9.12 μg/ml, 0.50 L/hr*kg, 0.24 hr^-1 and 134.45, 138.71 μg*hr/ml, 2.05, 13.01 hr, 16.57 μg/ml, 0.18 L/hr*kg, 0.14 hr^-1 in the serum and ileum fluid, respectively. The optimum doses for bacteriostatic, bactericidal, and elimination activities were 29.81, 34.88, and 36.52 mg/kg for 50% target and 33.95, 39.79, and 42.55 mg/kg for 90% target, respectively. The final sensitive breakpoint was defined as 16 μg/ml. The current data presented provide the optimal regimens (39.79 mg/kg) and susceptible breakpoint (16 μg/ml) for clinical use, but these predicted data should be validated in the clinical practice.

Bayesian population pharmacokinetic modeling of florfenicol in pigs after intravenous and intramuscular administration

Bayesian population pharmacokinetic models of florfenicol in healthy pigs were developed based on retrospective data in pigs either via intravenous (i.v.) or intramuscular (i.m.) administration. Following i.v. administration, the disposition of florfenicol was best described by a two-compartment open model with the typical values of half-life at α phase (t_1/2α ), half-life at β phase (t_1/2β ), total body clearance (Cl), and volume of distribution (V_d ) were 0.132 ± 0.0289, 2.78 ± 0.166 hr, 0.215 ± 0.0102, and 0.841 ± 0.0289 L kg^-1 , respectively. The disposition of florfenicol after i.m. administration was best described by a one-compartment open model. The typical values of maximum concentration of drug in serum (C_max ), elimination half-life (t_1/2Kel ), Cl, and Volume (V) were 5.52 ± 0.605 μg/ml, 9.96 ± 1.12 hr, 0.228 ± 0.0154 L hr^-1  kg^-1 , and 3.28 ± 0.402 L/kg, respectively. The between-subject variabilities of all the parameters after i.m. administration were between 25.1%-92.1%. Florfenicol was well absorbed (94.1%) after i.m. administration. According to Monte Carlo simulation, 8.5 and 6 mg/kg were adequate to exert 90% bactericidal effect against Actinobacillus pleuropneumoniae after i.v. and i.m. administration.

Florfenicol induces more severe hemotoxicity and immunotoxicity than equal doses of chloramphenicol and thiamphenicol in Kunming mice

Amphenicols are effective, broad-spectrum antibiotics that function by inhibiting the peptidyl transferase activity of bacteria, while the drugs can also inhibit mitochondrial protein synthesis in eukaryotes through the same mechanism, which leads to multi-organ toxicity. Some side effects of each drug have been studied, while differences in the severity of the hemotoxicities and immunotoxicities of amphenicols have not been reported. Thus, it is important to identify, evaluate, and compare the potential hemotoxicities and immunotoxicities to guide their proper use in humans and animals, which will guarantee food safety and animal welfare. Ovalbumin-immunized Kunming mice were gavaged daily with amphenicols for seven days. Blood samples were collected for hematology analysis, and measuring anti-ovalbumin antibody levels and serum intereukin-2 concentrations. The bone marrow, spleen and thymus were collected for histopathology and apoptosis analyzes. Bone marrow nucleated cells (BMNCs) and splenocytes were harvested to determine their cell cycle stages and to analyze lymphocyte proliferation. The results demonstrated that amphenicols, especially florfenicol (FLO), induced cell cycle arrest and apoptosis of hematopoietic cells, and it changed the bone marrow hematopoietic microenvironment by decreasing the number of peripheral blood cells. Moreover, amphenicols, especially FLO, induced hypoplasia and atrophy of the spleen and thymus, induced cell cycle arrest, as well as splenocyte apoptosis, and decreased the proliferation and viability of lymphocytes and the humoral and cellular immunity of the treated mice. These results suggest that amphenicols induce hemotoxicity and immunotoxicity to some extent, and that FLO induces more severe toxicity than equal doses of chloramphenicol (CAP) and thiamphenicol (TAP).

Toxicity to the hematopoietic and lymphoid organs of piglets treated with a therapeutic dose of florfenicol

Florfenicol (FLO) is a broad-spectrum antibacterial agent for treatment of bacteriosis of piglets in veterinary practice. To study the toxicity to the hematopoietic and lymphoid organs of piglets treated with a therapeutic dose of FLO, 20 healthy weaned piglets were selected and randomly divided into two groups. Piglets in the FLO group were fed with fodder supplemented with 30mg/kg BW of FLO twice a day for 10 days. Blood samples were drawn at four time points: 1 day before FLO administration and 1, 7, and 14 days post-withdrawal. Three or four piglets were euthanized at each time point post-withdrawal and tissue samples (bone marrow, thymus and spleen) were collected for fixation and cryostorage. The levels of classical swine fever virus (CSFV) antibody against the vaccine, the concentrations of Hsp70 and IL-6 in serum and Hsp70 in tissues, and the mRNA expression levels of B-cell lymphoma 2 (bcl-2) and tumor suppressor p53 were detected, the hematology of the piglets were analyzed, and the histopathology and the status of apoptosis of the hematopoietic and lymphoid organs was examined. The results showed changes in several indicators in the FLO group 1 day post-withdrawal: the concentration of red blood cells (RBCs) was decreased, and that of platelets (PLTs) was significantly lower (p<0.05); the volumes of RBC and PLT were increased; the sum of blood lymphocytes was statistically decreased (p<0.05); the concentration of IL-6 was significantly increased (p<0.05); the concentrations of Hsp70 in serum and tissues were increased; obvious atrophy of the hematopoietic cell lines and partial replacement by fat cells were observed in bone marrow; thymus and spleen tissues showed lower concentrations and sparser arrangement of lymphocytes in the thymic medulla and white pulp of the spleen respectively; and the mRNA expression levels of bcl-2 in the three tissues were up-regulated, while that of p53 was down-regulated. With time after cessation of FLO administration, the indicators of the FLO group gradually returned to close to that of the control group and the histological lesions of the tissues gradually recovered, and the differences in the densities of lymphocytes and cell arrangements in the tissues between two groups gradually decreased. In conclusion, a therapeutic dose of FLO induces temporary toxicity in the hematopoietic and lymphoid organs of piglets to some extent, and influences hemopoiesis and immune function. These effects gradually decrease after cessation of FLO administration.

Florfenicol impairs the immune responses to vaccination against foot-and-mouth disease in mice

Florfenicol is a new type of broad-spectrum antibacterial that has been used in veterinary clinics. It showed immunosuppressive activity on the immune responses to vaccination against foot-and-mouth disease virus (FMDV) serotype O in mice. In the present study, BALB/c mice were immunized subcutaneously with FMDV serotype O antigen on days 1 and 14. Beginning on day 21, mice were treated with a single daily oral dose of florfenicol (50, 100, and 200 mg/kg) for seven consecutive days. On day 28, blood samples were collected to analyze FMDV-specific immunoglobulin G (IgG), IgG1, and IgG2b antibodies, and splenocytes were harvested to assess lymphocyte proliferation, CD3(+) T- and CD19(+) B-lymphocyte subsets. The results presented here demonstrated that florfenicol not only significantly suppressed concanavalin A-, lipopolysaccharide-induced splenocyte proliferation but also decreased the percentage of CD19(+) B-cells in a dose-dependent manner and suppressed CD3(+) T-cell at high doses. Moreover, FMDV-specific IgG, IgG1, and IgG2b antibody levels in FMDV-immunized mice were reduced by florfenicol. These results suggested that florfenicol could suppress humoral and cellular immune responses to vaccination against foot-and-mouth disease (FMD) in mice.

Pharmacokinetics of florfenicol and its metabolite, florfenicol amine, in dogs

A study on the bioavailability and pharmacokinetics of florfenicol was conducted in six healthy dogs following a single intravenous (i.v.) or oral (p.o.) dose of 20 mg kg(-1) body weight (b.w.). Florfenicol concentrations in serum were determined by a high-performance liquid chromatography/mass spectrometry. Plasma concentration-time data after p.o. or i.v. administration were analyzed by a non-compartmental analysis. Following i.v. injection, the total body clearance was 1.03 (0.49) L kg(-1)h(-1) and the volume of distribution at steady-state was 1.45 (0.82) L kg(-1). Florfenicol was rapidly distributed and eliminated following i.v. injection with 1.11 (0.94)h of the elimination half-life. After oral administration, the calculated mean C(max) values (6.18 microg ml(-1)) were reached at 0.94 h in dogs. The elimination half-life of florfenicol was 1.24 (0.64) h and the absolute bioavailability (F) was achieved 95.43 (11.60)% after oral administration of florfenicol. Florfenicol amine, the major metabolite of florfenicol, was detected in all dogs after i.v. and p.o. administrations.

Pharmacokinetics of florfenicol and its major metabolite, florfenicol amine, in rabbits

The pharmacokinetics of florfenicol and its active metabolite florfenicol amine were investigated in rabbits after a single intravenous (i.v.) and oral (p.o.) administration of florfenicol at 20 mg/kg bodyweight. The plasma concentrations of florfenicol and florfenicol amine were determined simultaneously by an LC/MS method. After i.v. injection, the terminal half-life (t(1/2lambdaz)), steady-state volume of distribution, total body clearance and mean residence time of florfenicol were 0.90 +/- 0.20 h, 0.94 +/- 0.19 L/kg, 0.63 +/- 0.06 L/h/kg and 1.50 +/- 0.34 h respectively. The peak concentrations (C(max)) of florfenicol (7.96 +/- 2.75 microg/mL) after p.o. administration were observed at 0.90 +/- 0.38 h. The t(1/2lambdaz) and p.o. bioavailability of florfenicol were 1.42 +/- 0.56 h and 76.23 +/- 12.02% respectively. Florfenicol amine was detected in all rabbits after i.v. and p.o. administration. After i.v. and p.o. administration of florfenicol, the observed Cmax values of florfenicol amine (5.06 +/- 1.79 and 3.38 +/- 0.97 microg/mL) were reached at 0.88 +/- 0.78 and 2.10 +/- 1.08 h respectively. Florfenicol amine was eliminated with an elimination half-life of 1.84 +/- 0.17 and 2.35 +/- 0.94 h after i.v. and p.o. administration respectively.

Effect of Oral Enrofloxacin and Florfenicol on Pigs Experimentally Infected with Actinobacillus pleuropneumoniae Serotype 1

This study was carried out to compare the efficacy of two oral anti-microbials as metaphylactic medication to pigs inoculated with Actinobacillus pleuropneumoniae serotype 1. Forty-two pigs with an average weight of 22.64 kg were randomly assigned to three treatment groups: group F was given doses of 40 ppm of florfenicol, group E received 150 ppm of enrofloxacin and group C received no medication. Groups F and E received medicated feed 12 h before being inoculated and for 7 days after inoculation. All the pigs were inoculated by aerosol, with 2 x 10(7) CFU/ml of A. pleuropneumoniae serotype 1 each. The average body temperature was higher in group C than in groups E and F, between 12 and 96 h after inoculation (P < 0.05). No differences were found between groups F and E in respiration pattern, nasal secretion and general condition (P > 0.05): however, differences were found in group C for respiration pattern and general condition (P < 0.05), 12 h after inoculation. There was no mortality in groups F and E, whereas a 50% mortality was recorded in group C during the first 48 h after inoculation (P < 0.05). Necropsies and bacterial cultures were performed 12 days after inoculation. Lesions were observed in five pigs of group F (35.71%) with an average damage of 1.16%; in four pigs of group E (28.57%) with 1.24%; and in 13 animals in group C (92.85%) with 34.5% of affected lung tissue (P < 0.05). The infective agent was cultured from various organs of animals in groups F and C, but not from those in group E.

Tissue pharmacokinetics of florfenicol in pigs experimentally infected with Actinobacillus pleuropneumoniae

The aim of this study has been to determine the tissue pharmacokinetic parameters of florfenicol in the pigs experimentally infected with Actinobacillus pleuropneumoniae. 21 crossed-bred (Duroc x Landrace x Yorkshire) local species of pigs were infected experimentally with Actinobacillus pleuropneumoniae serotype 1 and confirmed as typical sub-acute pleuropneumonia. A single dose of 20 mg/kg body weight of florfenicol, a novel animal-using antibiotic, was administrated intramuscularly in the pigs and then samples of blood, lung, trachea with bronchi, liver, kidney and muscle were taken at scheduled time points. Drug concentrations were determined by high performance liquid chromatography (HPLC) with an ultraviolet detector via extraction with ethyl acetate under nitrogen flow. The statistic moment theory (SMT) mathematic package was applied to calculate the tissue pharmacokinetic parameters of florfenicol in the infected model. AUC of lung, trachea with bronchi, liver, kidney and muscle were 121.69, 79.37, 81.05, 181.2, and 94.07 mg/l x h, respectively, MRT were from 34.66 to 90.17 h, and t1/2beta from 24.75 to 69.34 h, respectively.

CONCLUSIONS

Florfenicol was widely distributed in these tissues and maintained the effective therapeutic concentrations especially in the respiratory tract tissues that are the target organs of Actinobacillus pneuropneumoniae.

CLINICAL SIGNIFICANCE

Tissue pharmacokinetic data could be evidence for regime designing of florfenicol in treatment of porcine pleuropneumonia.

Comparative in vitro activity of 16 antimicrobial agents against Actinobacillus pleuropneumoniae

Sixteen antimicrobial agents were tested for their activity against 68 isolates of Actinobacillus pleuropneumoniae by determining the minimum inhibitory concentrations (MICs). Ceftiofur and the fluoroquinolones danofloxacin and enrofloxacin were the most active compounds, with a MIC for 90% of the isolates (MIC90) of (0.05 microg/ml. The MIC90 values of benzylpenicillin, amoxicillin and aspoxicillin were 0.78 units/ml, 0.39 microg/ml and < or = 0.05 microg/ml, respectively. Three isolates (4.4%) were resistant to penicillins, but aspoxicillin was as active as ceftiofur against the susceptible isolates, with MICs of < or = 0.05 microg/ml for all isolates. Resistance to oxytetracycline, chloramphenicol and thiamphenicol occurred in 22 (32.4%), 14 (20.6%) and 15 (22.1%) of the isolates, respectively. Doxycycline was more active than oxytetracycline, with a MIC90 of 1.56 microg/ml as against 25 microg/ml. Florfenicol was not only as active as thiamphenicol, with a MIC for 50% of the isolates (MIC50) of 0.39 microg/ml, but also active against thiamphenicol-resistant isolates. All the isolates were susceptible to florfenicol. All the isolates were also susceptible to gentamicin, spectinomycin, tilmicosin, colistin and tiamulin. Of these, spectinomycin was the least active, with a MIC50 of 25 microg/ml, followed by tiamulin, with a MIC50 of 6.25 microg/ml. Of the 68 isolates tested, 49 (72.0%) were of serotype 2; 14 (20.5%) were of serotype 1; 2 each (3.0%) were of serotypes 5 and 6; and one was of serotype 7. Of the isolates, 23 (33.8%) were resistant to one or more of the major antibiotics. Antibiotic resistance was found only infrequently among serotype 2, with 5 (10.2%) of 49 isolates being resistant to chloramphenicol and/or oxytetracycline, while it occurred in 18 (94.7%) of the 19 isolates of other serotypes.

Pharmacokinetics of florfenicol after treatment of pigs with single oral or intramuscular doses or with medicated feed for three days

The pharmacokinetics of florfenicol, a structural analogue of thiamphenicol, were studied in six pigs after single oral and intramuscular doses of 15 mg/kg bodyweight, and after feeding them with medicated feed containing 250 mg/kg for three days, a concentration which provided approximately the same dose rate of the drug. The oral doses contained a specially prepared pelleted formulation of the drug. The bioavailability of the drug was similar for the oral and intramuscular doses. Florfenicol was absorbed rapidly from the feed and its concentration in plasma remained between 2 and 6 microg/ml - above the minimum inhibitory concentration values for common pig pathogens - during the three days.