Pharmacokinetics of florfenicol in cerebrospinal fluid and plasma of calves

Pharmacokinetics of florfenicol in serum and seminal plasma in beef bulls

The objectives of this study were to compare the serum and seminal plasma pharmacokinetic profiles of florfenicol (FLO) and florfenicol amine (FLA) after the administration of FLO either by IM or SC routes in beef bulls. Four clinically healthy Hereford bulls underwent a comprehensive physical exam, including breeding soundness examination, CBC, and chemistry profile panel. Bulls were healthy and classified satisfactory potential breeders. In one group (n = 2), a single dose of FLO was administered SC in the middle of the neck at a dose of 40 mg/kg of body weight. In the second group (n = 2), a single dose was administered IM in the muscles of the neck at a dose of 20 mg/kg. Concentrations of FLO and FLA in serum and seminal plasma were determined by ultra-high-performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). Blood and semen samples were collected before the administration of FLO and at 12, 24, 36, 48, 72, 96, 120, 144, and 168 h after injection. The blood was collected from the coccygeal vessels, and semen was collected by electroejaculation. All samples were immediately refrigerated, processed within the first hour after collection, and finally stored at -80 °C. The mean level of total FLO in serum was higher when administered by the SC route (1,415.5 ng/mL) than by the IM route (752.4 ng/mL; P = 0.001). Differences were observed between the percentage of FLA in serum (1.8%; ranging from 1.3 to 2.9) and in seminal plasma (27.5%; ranging from 15.9 to 34.2; P = 0.0001). The mean level (±SD) of FLA was higher in seminal plasma compared to serum (467 ± 466 ng/mL and 18 ± 16 ng/mL, respectively; P = 0.001). The mean level of total FLO in seminal plasma was 1,454.8 ng/mL for the SC route and 1,872.9 ng/mL for the IM route without differences between the two routes (P = 0.51). Differences in the mean level of total FLO between serum and seminal plasma were detected (1,187 ± 2,069 ng/mL and 1,748 ± 1,906 ng/mL, respectively; P = 0.04). From the present investigation, it was concluded that FLO is a suitable antibiotic based on its pharmacokinetic attributes and may be employed for the treatment of bull genital infections when its use is indicated. To study the pharmacokinetics of FLO in seminal plasma, the analysis of FLA should be incorporated.

A review on the antibiotic florfenicol: Occurrence, environmental fate, effects, and health risks

Florfenicol, as a replacement for chloramphenicol, can tightly bind to the A site of the 23S rRNA in the 50S subunit of the 70S ribosome, thereby inhibiting protein synthesis and bacterial proliferation. Due to the widespread use in aquaculture and veterinary medicine, florfenicol has been detected in the aquatic environment worldwide. Concerns over the effects and health risks of florfenicol on target and non-target organisms have been raised in recent years. Although the ecotoxicity of florfenicol has been widely reported in different species, no attempt has been made to review the current research progress of florfenicol toxicity, hormesis, and its health risks posed to biota. In this study, a comprehensive literature review was conducted to summarize the effects of florfenicol on various organisms including bacteria, algae, invertebrates, fishes, birds, and mammals. The generation of antibiotic resistant bacteria and spread antibiotic resistant genes, closely associated with hormesis, are pressing environmental health issues stemming from overuse or misuse of antibiotics including florfenicol. Exposure to florfenicol at μg/L-mg/L induced hormetic effects in several algal species, and chromoplasts might serve as a target for florfenicol-induced effects; however, the underlying molecular mechanisms are completely lacking. Exposure to high levels (mg/L) of florfenicol modified the xenobiotic metabolism, antioxidant systems, and energy metabolism, resulting in hepatotoxicity, renal toxicity, immunotoxicity, developmental toxicity, reproductive toxicity, obesogenic effects, and hormesis in different animal species. Mitochondria and the associated energy metabolism are suggested to be the primary targets for florfenicol toxicity in animals, albeit further in-depth investigations are warranted for revealing the long-term effects (e.g., whole-life-cycle impacts, multigenerational effects) of florfenicol, especially at environmental levels, and the underlying mechanisms. This will facilitate the evaluation of potential hormetic effects and construction of adverse outcome pathways for environmental risk assessment and regulation of florfenicol.

Florfenicol and Florfenicol Amine Quantification in Bull Serum and Seminal Plasma by a Single Validated UHPLC-MS/MS Method

Florfenicol is a broad-spectrum antibiotic belonging to the amphenicols class that inhibits protein synthesis by binding to bacteria's ribosomal subunits. This drug is commonly used in veterinary medicine to treat bacterial infectious diseases in cattle, swine, poultry, and fish. The proposed method uses a quick protein precipitation with acetonitrile for the extraction of florfenicol and florfenicol amine in serum and seminal plasma, followed by analysis in UHPLC-MS/MS for their simultaneous quantification. A BEH C18 reversed-phase column was chosen for analyte separation, allowing to obtaining sharp and symmetrical peak shapes in a chromatographic run of just 3.5 min under programmed conditions. Two specific transitions were observed for each analyte, and florfenicol-d3 was used as the internal standard. The approach was fully validated in each matrix over ranges suitable for field concentrations of florfenicol and florfenicol amine, showing good linearity during each day of testing (R² always >0.99). Excellent accuracy and precision were demonstrated, for both analytes, by calculated bias always within ±15% and CV% always below 15% at all QC levels tested. The satisfactory outcomes obtained during recovery, matrix effect, and process efficiency investigations in serum and seminal plasma confirmed the strength of the method for the quantification of target compounds. To our knowledge, this is the first LC-MS/MS-validated approach for the quantification of florfenicol and florfenicol amine in serum and seminal plasma and was successfully applied for the determination of their concentration-time profiles in bulls. This paves the way to understanding the pharmacokinetics of this antibiotic and its active metabolite in bull's seminal plasma, which will enable the design of more appropriate treatment protocols.

Pharmaceutical characterization and pharmacokinetics of florfenicol-loaded alginate dried beads in rabbits

The pharmacokinetic variables of a new formulation of florfenicol included in dried bean of alginate (FADBs), its acceptance as in food medication, and its relationship with theoretical minimum inhibitory concentration (MIC) values of the main pathogens in rabbits, are presented. FADBs sought to mask the unpleasant taste of florfenicol while enhancing sustained absorption in a day to facilitate and optimise its dosage in this species. The entrapment efficiency was determined to be 94-98% and 73.56±3.26% of drug loading. No reduction in food consumption was detected, nor selectivity when choosing from their usual food. The elimination half-life was 1.23 to 2.4 h slower than the one previously reported in the literature. Possible flip-flop pharmacokinetics is proposed for FADBs in rabbits, thus complying better with the key pharmacokinetics/pharmacodynamics (PK/PD) ratio of t≥MIC. Also, if a MIC2.0 μg/mL is taken as the cut-off point for florfenicol in rabbits, then ad libitum intake of FADBs in their standard diet is sufficient to maintain plasma concentrations of florfenicol above this level during the whole dosing interval of 24 h. Additionally, FADBs are a low-cost and attractive drug delivery system for the oral controlled release of florfenicol in rabbits.

An Interactive Generic Physiologically Based Pharmacokinetic (igPBPK) Modeling Platform to Predict Drug Withdrawal Intervals in Cattle and Swine: A Case Study on Flunixin, Florfenicol and Penicillin G

Violative chemical residues in edible tissues from food-producing animals are of global public health concern. Great efforts have been made to develop physiologically based pharmacokinetic (PBPK) models for estimating withdrawal intervals (WDIs) for extralabel prescribed drugs in food animals. Existing models are insufficient to address the food safety concern as these models are either limited to 1 specific drug or difficult to be used by non-modelers. This study aimed to develop a user-friendly generic PBPK platform that can predict tissue residues and estimate WDIs for multiple drugs including flunixin, florfenicol, and penicillin G in cattle and swine. Mechanism-based in silico methods were used to predict tissue/plasma partition coefficients and the models were calibrated and evaluated with pharmacokinetic data from Food Animal Residue Avoidance Databank (FARAD). Results showed that model predictions were, in general, within a 2-fold factor of experimental data for all 3 drugs in both species. Following extralabel administration and respective U.S. FDA-approved tolerances, predicted WDIs for both cattle and swine were close to or slightly longer than FDA-approved label withdrawal times (eg, predicted 8, 28, and 7 days vs labeled 4, 28, and 4 days for flunixin, florfenicol, and penicillin G in cattle, respectively). The final model was converted to a web-based interactive generic PBPK platform. This PBPK platform serves as a user-friendly quantitative tool for real-time predictions of WDIs for flunixin, florfenicol, and penicillin G following FDA-approved label or extralabel use in both cattle and swine, and provides a basis for extrapolating to other drugs and species.

Comparative pharmacokinetics of two florfenicol formulations following intramuscular and subcutaneous administration to sheep

OBJECTIVE To compare the pharmacokinetics of 2 commercial florfenicol formulations following IM and SC administration to sheep. ANIMALS 16 healthy adult mixed-breed sheep. PROCEDURES In a crossover study, sheep were randomly assigned to receive florfenicol formulation A or B at a single dose of 20 mg/kg, IM, or 40 mg/kg, SC. After a 2-week washout period, each sheep was administered the opposite formulation at the same dose and administration route as the initial formulation. Blood samples were collected immediately before and at predetermined times for 24 hours after each florfenicol administration. Plasma florfenicol concentrations were determined by high-performance liquid chromatography. Pharmacokinetic parameters were estimated by noncompartmental methods and compared between the 2 formulations at each dose and route of administration. RESULTS Median maximum plasma concentration, elimination half-life, and area under the concentration-time curve from time 0 to the last quantifiable measurement for florfenicol were 3.76 μg/mL, 13.44 hours, and 24.88 μg•h/mL, respectively, for formulation A and 7.72 μg/mL, 5.98 hours, and 41.53 μg•h/mL, respectively, for formulation B following administration of 20 mg of florfenicol/kg, IM, and 2.63 μg/mL, 12.48 hours, and 31.63 μg•h/mL, respectively, for formulation A and 4.70 μg/mL, 16.60 hours, and 48.32 μg•h/mL, respectively, for formulation B following administration of 40 mg of florfenicol/kg, SC. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that both formulations achieved plasma florfenicol concentrations expected to be therapeutic for respiratory tract disease caused by Mannheimia haemolytica or Pasteurella spp at both doses and administration routes evaluated.

Tilmicosin- and florfenicol-loaded hydrogenated castor oil-solid lipid nanoparticles to pigs: Combined antibacterial activities and pharmacokinetics

The combined antibacterial effects of tilmicosin (TIL) and florfenicol (FF) against Actinobacillus pleuropneumoniae (APP) (n = 2), Streptococcus suis (S. suis) (n = 2), and Haemophilus parasuis (HPS) (n = 2) were evaluated by chekerboard test and time-kill assays. The pharmacokinetics (PKs) of TIL- and FF-loaded hydrogenated castor oil (HCO)-solid lipid nanoparticles (SLN) were performed in healthy pigs. The results indicated that TIL and FF showed synergistic or additive antibacterial activities against APP, S. suis and HPS with the fractional inhibitory concentration (FIC) ranging from 0.375 to 0.75. The time-kill assays showed that 1/2 minimum inhibitory concentration (MIC) TIL combined with 1/2 MIC FF had a stronger ability to inhibit the growth of APP, S. suis, and HPS than 1 MIC TIL or 1 MIC FF, respectively. After oral administration, plasma TIL and FF concentrations could maintain about 0.1 μg/ml for 192 and 176 hr. The SLN prolonged the last time point with detectable concentrations (T_last ), area under the concentration-time curve (AUC_0-t ), elimination half-life (T_½ke ), and mean residence time (MRT) by 3.1, 5.6, 12.7, 3.4-fold of the active pharmaceutical ingredient (API) of TIL and 11.8, 16.5, 18.1, 12.1-fold of the API of FF, respectively. This study suggests that the TIL-FF-SLN could be a useful oral formulation for the treatment of APP, S. suis, and HPS infection in pigs.

Development of a high-performance liquid chromatography method for the determination of florfenicol in animal feedstuffs

An effective thin layer chromatography (TLC) purification procedure coupled to high-performance liquid chromatography (HPLC) method was developed for the determination of florfenicol (FF) in pig, chicken and fish feedstuffs. The feedstuff samples were extracted with ethyl acetate, defatted with n-hexane saturated with acetonitrile, and further purified by TLC. The chromatographic separation was performed on a Waters Symmetry C₁₈ column using an isocratic procedure with acetonitrile-water (35:65, v/v) at 0.6mL/min. The ultraviolet (UV) detector was set at a wavelength of 225nm. The FF concentrations in feedstuff samples were quantified using a standard curve. Good linear correlations (y=159075x-15054, r>0.9999) were achieved within the concentration range of 0.05-200μg/mL. The recoveries of FF spiked at levels of 1, 100 and 1000μg/g ranged from 80.6% to 105.3% with the intra-day and inter-day relative standard deviation (RSD) less than 9.3%. The limit of detection (LOD) and limit of quantitation (LOQ) were 0.02 and 0.06mg/kg for pig feedstuffs, 0.02 and 0.07mg/kg for chicken feedstuffs, and 0.02 and 0.05mg/kg for fish feedstuffs, respectively. This reliable, simple and cost-effective method could be applied to the routine monitoring of FF in animal feedstuffs.

Pharmacokinetic model of florfenicol in turbot (Scophthalmus maximus): establishment of optimal dosage and administration in medicated feed

The pharmacokinetics of florfenicol (FF) in turbot (Scophthalmus maximus) was studied after single intravenous (10 mg kg^-1 ) and oral (100 mg kg^-1 ) administration. The plasma concentration-time data of florfenicol were described by an open one-compartment model. The elimination half-life (t_1/2 ) was estimated to be 21.0 h, and the total body clearance, Cl, was determined as 0.028 L kg h^-1 . The apparent volume distribution (V_d ) was calculated to be 0.86 L kg^-1 and the mean residence time (MRT_iv ) was 30.2 h. Following oral administration, the maximum plasma concentration (C_max ) of 55.4 μg mL^-1 was reached at 12 h (T_max ). The absorption constant (k_a ) was 0.158 h^-1 . The bioavailability was estimated to be 57.1%. The low bioavailability observed at higher doses was explained by the saturation of the mechanisms of absorption. The drug absorption process was limited by its inherent low solubility, which limited the amount of available FF absorbed in the gastrointestinal tract. Based on the pharmacokinetic data, an optimal dosing schedule for FF administration is hereby provided. Based on the minimum inhibitory concentration found for susceptible strains of Aeromonas salmonicida, oral FF administration of first, an initial dose of 30 mg FF kg^-1 , followed by 6 maintenance doses at 18 mg kg^-1 /daily could be effective against furunculosis in turbot.

Plasma and tissue disposition of florfenicol in Escherichia coli lipopolysaccharide-induced endotoxaemic sheep

1. The purpose of this study was to understand the effects of the acute inflammatory response (AIR) induced by Escherichia coli lipopolysaccharide (LPS) on florfenicol (FFC) and FFC-amine (FFC-a) plasma and tissue concentrations. 2. Ten Suffolk Down sheep, 60.5 ± 4.7 kg, were distributed into two experimental groups: group 1 (LPS) treated with three intravenous doses of 1 μg/kg bw of LPS at 24, 16, and 0.75 h (45 min) before FFC treatment; group 2 (Control) was treated with saline solution (SS) in parallel to group 1. An IM dose of 20 mg FFC/kg was administered at 0.75 h after the last injection of LPS or SS. Blood and tissue samples were taken after FFC administration. 3. The plasma AUC_0-4 h values of FFC were higher (p = 0.0313) in sheep treated with LPS (21.8 ± 2.0 μg·min/mL) compared with the control group (12.8 ± 2.3 μg·min/mL). Lipopolysaccharide injections increased FFC concentrations in kidneys, spleen, and brain. Low levels of plasma FFC-a were observed in control sheep (C_max = 0.14 ± 0.01 μg/mL) with a metabolite ratio (MR) of 4.0 ± 0.87%. While in the LPS group, C_max increased slightly (0.25 ± 0.01 μg/mL), and MR decreased to 2.8 ± 0.17%. 4. The changes observed in the plasma and tissue concentrations of FFC were attributed to the pathophysiological effects of LPS on renal hemodynamics that modified tissue distribution and reduced elimination of the drug.

Chloramphenicol Derivatives as Antibacterial and Anticancer Agents: Historic Problems and Current Solutions

Chloramphenicol (CAM) is the D-threo isomer of a small molecule, consisting of a p-nitrobenzene ring connected to a dichloroacetyl tail through a 2-amino-1,3-propanediol moiety. CAM displays a broad-spectrum bacteriostatic activity by specifically inhibiting the bacterial protein synthesis. In certain but important cases, it also exhibits bactericidal activity, namely against the three most common causes of meningitis, Haemophilus influenzae, Streptococcus pneumoniae and Neisseria meningitidis. Resistance to CAM has been frequently reported and ascribed to a variety of mechanisms. However, the most important concerns that limit its clinical utility relate to side effects such as neurotoxicity and hematologic disorders. In this review, we present previous and current efforts to synthesize CAM derivatives with improved pharmacological properties. In addition, we highlight potentially broader roles of these derivatives in investigating the plasticity of the ribosomal catalytic center, the main target of CAM.

Florfenicol concentrations in ovine tear fluid following intramuscular and subcutaneous administration and comparison with the minimum inhibitory concentrations against mycoplasmal strains potentially involved in infectious keratoconjunctivitis

OBJECTIVE

To measure florfenicol concentrations in ovine tear fluid after IM and SC administration and determine minimum inhibitory concentrations (MICs) of florfenicol against field isolates of Mycoplasma organisms potentially involved in infectious keratoconjunctivitis.

ANIMALS

9 healthy adult Lacaune ewes.

PROCEDURES

Animals received an IM and SC administration of florfenicol (20 mg/kg) in a 2-way crossover design. Samples of blood and tear fluid were collected before and for 24 hours after administration. Concentrations of florfenicol in plasma and tear fluid were measured via high-performance liquid chromatography. The MIC of florfenicol for various Mycoplasma strains cultured from sheep and goats was determined via an agar dilution method.

RESULTS

Mean florfenicol concentration in tear fluid for the 24-hour period was significantly higher after IM administration (0.70 μg/mL) than after SC administration (0.22 μg/mL) and was maintained for a longer duration. The lacrimal fluid-to-plasma concentration ratio was not different between the 2 routes of administration, with mean values of 40.2% and 32.5% after IM and SC administration, respectively. The MIC for Mycoplasma agalactiae, Mycoplasma conjunctivae, and Mycoplasma mycoides isolates ranged from 0.5 to 8 μg of florfenicol/mL. Two strains of M agalactiae could be considered resistant to florfenicol.

CONCLUSIONS AND CLINICAL RELEVANCE

Florfenicol readily penetrated the preocular tear fluid of sheep after IM and SC administration. For both routes of administration, doses > 20 mg/kg would be necessary to achieve tear fluid concentrations of florfenicol greater than the MICs for most strains of Mycoplasma organisms.

Pharmacodynamics of florfenicol for calf pneumonia pathogens

The antimicrobial properties of florfenicol were investigated for the bovine respiratory tract pathogens, Mannheimia haemolytica and Pasteurella multocida. Three in vitro indices of efficacy and potency were determined; minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and in vitro time-kill curves for six pathogenic strains of each organism. Each was monitored in two matrices, Mueller Hinton broth (MHB) and calf serum. MBC:MIC ratios were low, 1.8 : 1 for M haemolytica in both MHB and serum and 2.4 : 1 and 2.1 : 1 for P multocida in MHB and serum, respectively. The killing action of florfenicol had the characteristics of concentration dependency against M haemolytica and codependency (on time and concentration) against P multocida. Modelling of the time-kill data after 24 hours exposure was undertaken to quantify three levels of activity for the ratio, area under concentration-time curve over 24 hours (AUC24h)/MIC; bacteriostatic action (no change in bacterial count), 3log10 reduction and 4log10 reduction in bacterial count. Mean AUC24h/MIC values for P multocida in MHB (and serum) were 22.0 (23.3) hour, 34.5 (39.9) hour and 45.8 (50.4) hour, respectively. Similar numerical values were obtained for M haemolytica. For both bacterial species, interstrain variability was low; coefficients of variation ( per cent) in serum for 3log10 and 4log10 reductions in count were, respectively, 14.3 and 24.1 for P multocida and 7.8 and 11.4 for M haemolytica. These data form a rational basis for dosage selection for treatment of calf pneumonia caused by M haemolytica or P multocida.

Florfenicol pharmacokinetics in healthy adult alpacas after subcutaneous and intramuscular injection

A single dose of florfenicol (Nuflor(®)) was administered to eight healthy adult alpacas at 20 mg/kg intramuscular (i.m.) and 40 mg/kg subcutaneous (s.c.) using a randomized, cross-over design, and 28-day washout period. Subsequently, 40 mg/kg florfenicol was injected s.c. every other day for 10 doses to evaluate long-term effects. Maximum plasma florfenicol concentrations (C(max), measured via high-performance liquid chromatography) were achieved rapidly, leading to a higher C(max) of 4.31±3.03 μg/mL following administration of 20 mg/kg i.m. than 40 mg/kg s.c. (C(max): 1.95±0.94 μg/mL). Multiple s.c. dosing at 48 h intervals achieved a C(max) of 4.48±1.28 μg/mL at steady state. The area under the curve and terminal elimination half-lives were 51.83±11.72 μg/mL·h and 17.59±11.69 h after single 2 mg/kg i.m. dose, as well as 99.78±23.58 μg/mL·h and 99.67±59.89 h following 40 mg/kg injection of florfenicol s.c., respectively. Florfenicol decreased the following hematological parameters after repeated administration between weeks 0 and 3: total protein (6.38 vs. 5.61 g/dL, P<0.0001), globulin (2.76 vs. 2.16 g/dL, P<0.0003), albumin (3.61 vs. 3.48 g/dL, P=0.0038), white blood cell count (11.89 vs. 9.66×10(3)/μL, P<0.044), and hematocrit (27.25 vs. 24.88%, P<0.0349). Significant clinical illness was observed in one alpaca. The lowest effective dose of florfenicol should thus be used in alpacas and limited to treatment of highly susceptible pathogens.

Septicemia and meningitis in the newborn calf

Neonatal infections and sepsis occur most frequently in calves with failure of passive transfer. If the invading bacteria are not rapidly controlled, they can set up focal infections, such as in growth plates, joints, or meninges, or generalized sepsis may occur. If not successfully treated, sepsis can lead to a systemic inflammatory response, multiple organ dysfunction syndromes, septic shock, and death. Treatments are based on selecting an appropriate antimicrobial drug and dosage, supportive therapy, fluid therapy, nonsteroidal anti-inflammatory drugs, and plasma transfusion. Preventing the failure of passive transfer through good colostrum management is essential.

Plasma and tissue depletion of florfenicol and florfenicol-amine in chickens

Chickens were used to investigate plasma disposition of florfenicol after single intravenous (i.v.) and oral dose (20 mg kg-1 body weight) and to study residue depletion of florfenicol and its major metabolite florfenicol-amine after multiple oral doses (40 mg kg-1 body weight, daily for 3 days). Plasma and tissue samples were analyzed using a high-performance liquid chromatography (HPLC) method. After i.v. and oral administration, plasma concentration-time curves were best described by a two-compartment open model. The mean [ +/- standard deviation (SD)] elimination half-life (t1/2beta) of florfenicol in plasma was 7.90 +/- 0.48 and 8.34 +/- 0.64 h after i.v. and oral administration, respectively. The maximum plasma concentration was 10.23 +/- 1.67 microg mL-1, and the interval from oral administration until maximal concentration was 0.63 +/- 0.07 h. Oral bioavailability was found to be 87 +/- 16%. Florfenicol was converted to florfenicol-amine. After multiple oral dose (40 mg kg-1 body weight, daily for 3 days), in kidney and liver, concentrations of florfenicol (119.34 +/- 31.81 and 817.34 +/- 91.65 microg kg-1, respectively) and florfenicol-amine (60.67 +/- 13.05 and 48.50 +/- 13.07 microg kg-1, respectively) persisted for 7 days. The prolonged presence of residues of florfenicol and florfenicol-amine in edible tissues can play an important role in human food safety, because the compounds could give rise to a possible health risk. A withdrawal time of 6 days was necessary to ensure that the residues of florfenicol were less than the maximal residue limits or tolerance established by the European Union.

D-Lactic acid-induced neurotoxicity in a calf model

Lactic acidosis (DAC) occurs as a complication of short-bowel syndrome in humans and in a variety of other gastrointestinal disorders in monogastrics and ruminants. DAC is associated with signs of impaired central nervous system (CNS) function including ataxia and coma. The objective of this experiment was to determine whether either acidification of nervous tissue or d-lactic acid is responsible for decreased neurological function. Eight Holstein calves (32 +/- 11 days, 70 +/- 10 kg) were surgically catheterized with indwelling intravenous jugular and atlanto-occipital space cerebrospinal fluid (CSF) catheters and infused for 6 h in random order with isomolar dl-lactic acid (dl-LA), l-lactic acid (l-LA), hydrochloric acid (HCl), or saline. dl-LA induced ataxia after 4 h of infusion and produced the greatest obtunding of CNS function (at 7 h, score 8.0 +/- 0.4), whereas the other infusions caused neither ataxia nor scores over 1.5 (P < 0.01 from dl-LA). dl-LA induced significantly less acidemia than HCl (at 6 h pH 7.13 +/- 0.06 and 7.00 +/- 0.04, base excess -16 +/- 1 and -23 +/- 3 mmol/l, bicarbonate 11 +/- 1 and 8 +/- 1 mmol/l respectively, all P < 0.01) but greater than l-LA and saline (P < 0.01). CSF changes followed a similar but less pronounced pattern. Although HCl infusion produced a severe acidemia and CSF acidosis, only minor effects on neurological function were evident suggesting that d-lactate has a direct neurotoxic effect that is independent of acidosis. Conversely, l-LA produced only minor neurological changes.

Comparative evaluation between capillary electrophoresis and high-performance liquid chromatography for the analysis of florfenicol in plasma

A capillary electrophoresis (CE) and a reversed phase high-performance liquid chromatography (RP-HPLC) method with UV detection have been developed for florfenicol analysis in plasma samples. The suitabilities of both methods for quantitative determination of florfenicol were approved through validation specification, such as linearity, precision, selectivity, accuracy, limit of detection and quantification. The capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC) assay were compared by analyzing a series of plasma samples containing florfenicol in different concentrations using the two methods. The extraction procedure is simple and no gradient elution or derivatization is required. Furthermore, the analysis time of the CE method is two times shorter than the respective parameter in HPLC and solvent consumptions is considerably lower. The calibration curve were linear to at least 0.05-10 microg/ml (r = 0.9998) and 0.1-10 microg/ml (r = 0.9998) for CE and HPLC, respectively. The separation efficiency are good for both methods. The detection limits for florfenicol were 0.015 microg/ml with CE and 0.03 microg/ml with HPLC and CE method gave lower value, even though UV detector was applied in the both cases. The both methods were selective, robust and reliable quantification of florfenicol and can be useful for clinical and biomedical investigations.

Optimization and validation of a micellar electrokinetic chromatographic method for the analysis of florfenicol

We have optimized a micellar electrokinetic capillary chromatographic method for the separation of florfenicol and florfenicol amine, its degradation product. The separation was carried out using a 50mM sodium borate buffer (pH 9.0) containing 25mM of sodium dodecyl sulphate. The method selectivity was proven by the simultaneous separation of florfenicol and two structural antibiotics, chloramphenicol and thiamphenicol. The same system can also be applied for the quantitative determination of these antibiotics. The method was then validated regarding linearity, precision and accuracy.

Bacterial meningitis and encephalitis in ruminants

The clinical aspects of bacterial meningitis in neonates are described in this article. Specific types of meningitis affecting adult cattle are also described. Other conditions occurring less frequently,such as frontal sinusitis and brain abscess, are discussed.

Bioavailability and pharmacokinetics of florfenicol in healthy sheep*

A study on bioavailability and pharmacokinetics of florfenicol was conducted in 20 crossbred healthy sheep following a single intravenous (i.v.) and intramuscular (i.m.) doses of 20 and 30 mg/kg body weight (b.w.). Florfenicol concentrations in serum were determined by a validated high-performance liquid chromatography method with UV detection at a wavelength of 223 nm in which serum samples were spiked with chloramphenicol as internal standard. Serum concentration-time data after i.v. administration were best described by a three-compartment open model with values for the distribution half-lives (T(1/2alpha)) 1.51 +/- 0.06 and 1.59 +/- 0.10 h, elimination half-lives (T(1/2beta)) 18.83 +/- 6.76 and 18.71 +/- 1.85 h, total body clearance (Cl(B)) 0.26 +/- 0.03 and 0.25 +/- 0.01 L/kg/h, volume of distribution at steady-state (V(d(ss))) 1.86 +/- 0.11 and 1.71 +/- 0.20 L/kg, area under curve (AUC) 76.31 +/- 9.17 and 119.21 +/- 2.05 microg.h/mL after i.v. injections of 20 and 30 mg/kg b.w. respectively. Serum concentration-time data after i.m. administration were adequately described by a one-compartment open model. The pharmacokinetic parameters were distribution half-lives (T(1/2k(a) )) 0.27 +/- 0.03 and 0.25 +/- 0.09 h, elimination half-lives (T(1/2k(e) )) 10.34 +/- 1.11 and 9.57 +/- 2.84 h, maximum concentrations (C(max)) 4.13 +/- 0.29 and 7.04 +/- 1.61 microg/mL, area under curve (AUC) 67.95 +/- 9.61 and 101.95 +/- 8.92 microg.h/mL, bioavailability (F) 89.04% and 85.52% after i.m. injections of 20 and 30 mg/kg b.w. respectively.

Antimicrobial use in the treatment of calf diarrhea

Calves with diarrhea often have small intestinal overgrowth with Escherichia coli bacteria, regardless of the inciting cause for the diarrhea, and 30% of systemically ill calves with diarrhea have bacteremia, predominantly because of E coli. Antimicrobial treatment of diarrheic calves should therefore be focused against E coli in the small intestine and blood, the 2 sites of infection. Fecal bacterial culture and antimicrobial susceptibility testing is not recommended in calves with diarrhea because fecal bacterial populations do not accurately reflect small intestinal or blood bacterial populations and because the break points for susceptibility test results have not been validated. Antimicrobial efficacy is therefore best evaluated by the clinical response of a number of calves to treatment, with calves randomly assigned to treatment groups. Amoxicillin, chlortetracycline, neomycin, oxytetracycline, streptomycin, sulfachloropyridazine, sulfamethazine, and tetracycline administered PO are currently labeled in the United States for the treatment of calf diarrhea. On the basis of published evidence for the oral administration of these antimicrobial agents, only amoxicillin can be recommended for the treatment of diarrhea. Dosage recommendations are amoxicillin trihydrate (10 mg/kg PO q12h) or amoxicillin trihydrate-clavulanate potassium (12.5 mg combined drug/kg PO q12h) for at least 3 days; the latter constitutes extra-label drug use. Parenteral administration of broad-spectrum beta-lactam antimicrobials--ceftiofur (2.2 mg/kg IM or SC q12h) and amoxicillin or ampicillin (10 mg/kg IM q12h)--or potentiated sulfonamides (25 mg/kg IV or IM q24h) is recommended for treating calves with diarrhea and systemic illness; both constitute extra-label drug use. In calves with diarrhea and no systemic illness (normal appetite for milk, no fever), it is recommended that the health of the calf be monitored and that oral or parenteral antimicrobials not be administered.

Antimicrobial use in the treatment of calf diarrhea

Calves with diarrhea often have small intestinal overgrowth with Escherichia coli bacteria, regardless of the inciting cause for the diarrhea, and 30% of systemically ill calves with diarrhea have bacteremia, predominantly because of E coli. Antimicrobial treatment of diarrheic calves should therefore be focused against E coli in the small intestine and blood, the 2 sites of infection. Fecal bacterial culture and antimicrobial susceptibility testing is not recommended in calves with diarrhea because fecal bacterial populations do not accurately reflect small intestinal or blood bacterial populations and because the break points for susceptibility test results have not been validated. Antimicrobial efficacy is therefore best evaluated by the clinical response of a number of calves to treatment, with calves randomly assigned to treatment groups. Amoxicillin, chlortetracycline, neomycin, oxytetracycline, streptomycin, sulfachloropyridazine, sulfamethazine, and tetracycline administered PO are currently labeled in the United States for the treatment of calf diarrhea. On the basis of published evidence for the oral administration of these antimicrobial agents, only amoxicillin can be recommended for the treatment of diarrhea. Dosage recommendations are amoxicillin trihydrate (10 mg/kg PO q12h) or amoxicillin trihydrate‐clavulanate potassium (12.5 mg combined drug/kg PO q12h) for at least 3 days; the latter constitutes extra‐label drug use. Parenteral administration of broad‐spectrum β‐lactam antimicrobials–eftiofur (2.2mg/kg IM orSCq12h) and amoxicillin or ampicillin (10 mg/kg IM q12h)–rpotentiatedsulfonamides(25 mg/kg IV or IM q24h) is recommended for treating calves with diarrhea and systemic illness; both constitute extra‐label drug use. In calves with diarrhea and no systemic illness (normal appetite for milk, no fever), it is recommended that the health of the calf be monitored and that oral or parenteral antimicrobials not be administered.

Comparative plasma pharmacokinetics and tolerance of florfenicol following intramuscular and intravenous administration to camels, sheep and goats

Florfenicol, a monofluorinated analogue of thiamphenicol, has a broad antibacterial spectrum. The pharmacokinetics of florfenicol was studied following a single intravenous (i.v.) or intramuscular (i.m.) injection at a dose of 20 mg/kg body weight in healthy male camels, sheep and goats. The concentration of florfenicol in plasma was determined using a microbiological assay. Pharmacokinetic analysis was performed using a two-compartment open model. Following i.m. administration, the maximum plasma concentration of florfenicol (Cmax) reached in camels, sheep and goats was 0.84 +/- 0.08, 1.04 +/- 0.10 and 1.21 +/- 0.10 microg/ml, respectively, the the time required to reach Cmax (t(max)) in the same three respective species was 1.51 +/- 0.14, 1.44 +/- 0.10 and 1.21 +/- 0.10 h. The terminal half-life (t(1/2)beta) and the fraction of the drug absorbed (F%) in camels, sheep and goats were 151.3 +/- 16.33, 137.0 +/- 12.16 and 127.4 +/- 11.0 min, and 69.20% +/- 7.8% , 65.82% +/- 6.7% and 60.88% +/- 5.9%, respectively. The MRT in the same three respective species was 4.01 +/- 0.45, 3.42 +/- 0.39 and 2.98 +/- 0.32 h. Following i.v. administration, the terminal half-life (t(1/2)beta) and total body clearance (Clbeta) in camels, sheep and goats were 89.5 +/- 9.2, 78.8 +/- 8.3 and 71.1 +/- 8.9 min and 0.33 +/- 0.04, 0.30 +/- 0.03 and 0.27 +/- 0.03 L/h per kg, respectively. The area under the curve (AUC(0-infinity)) and the mean residence time (MRT) in the same three respective species were 60.61 +/- 6.98, 62.45 +/- 6.56 and 74.07 +/- 7.85 microg/ml per h, and 2.71 +/- 0.31, 2.34 +/- 0.25 and 2.11 +/- 0.23 h. These data suggest that sheep and goats absorb and clear florfenicol to a broadly similar extent, but the rate and extent of absorption of the drug tends to be higher in camels. Drug treatment caused no clinically overt adverse effects. Plasma enzyme activities and metabolites indicative of hepatic and renal functions measured 1, 2, 4 and 7 days following the drug treatment were within the normal range, indicating that the drug is safe at the dose used.

Susceptibility testing for bovine respiratory and enteric disease

The interpretation of susceptibility results for antimicrobials with NCCLS-approved veterinary-specific breakpoints and where the methods also were NCCLS-approved are well established. When these same breakpoints are applied to other applications, however, the interpretation is not so clear. In these cases, a finding of S based on serial-dilution breakpoints puts the isolate in a defined population of bacteria with an MIC equal to or below the S breakpoint. An R result, in these cases, indicates that the organism may have an MIC equal to or greater (with no limits) than the R breakpoint. Extended-dilution testing yields more specific information about the isolate MIC. The relationship of disk-diffusion zone diameters to serial-dilution MICs is correlated on the basis of specific bacterial populations. When disk-diffusion results are interpreted for isolates other than those used for interpretive criteria development, the clinician is left wondering if the zone-diameter results now have a different relationship to serial-dilution results. Furthermore, the question of predictive value of the serial-dilution break-points still remains. The veterinary clinician should be aware of the differences in susceptibility testing predictive value for different applications. When approved veterinary-specific interpretive criteria are not available, then it is appropriate to keep records of clinical response related to susceptibility testing results for common therapies. Advice should be sought on the relationship of pathogen MICs to pharmacokinetic-pharmacodynamic parameters in these situations.

Pharmacokinetics of florfenicol in healthy pigs and in pigs experimentally infected with Actinobacillus pleuropneumoniae

A comparative in vivo pharmacokinetic study of florfenicol was conducted in 18 crossbred pigs infected with Actinobacillus pleuropneumoniae following intravenous (i.v.), intramuscular (i.m.), or oral (p.o.) administration of a single dose of 20 mg/kg. The disease model was confirmed by clinical signs, X rays, pathohistologic examinations, and organism isolation. Florfenicol concentrations in plasma were determined by a validated high-performance liquid chromatography method with UV detection at a wavelength of 223 nm. Pharmacokinetic parameters were calculated by using the MCPKP software (Research Institute of Traditional Chinese Veterinary Medicine, Lanzhou, China). The disposition of florfenicol after a single i.v. bolus was described by a two-compartment model with values for the half-life at alpha phase (t(1/2alpha)), the half-life at beta phase (t(1/2beta)), the area under the concentration-time curve (AUC(0- infinity )), and the volume of distribution at steady state (V(ss)) of 0.37 h, 2.91 h, 64.86 micro g. h/ml, and 1.2 liter/kg, respectively. The concentration-time data fitted the one-compartment (after i.m.) and two-compartment (after p.o.) models with first-order absorption. The values for the maximum concentration of drug in serum (C(max)), t(1/2alpha), t(1/2beta), and bioavailability after i.m. and p.o. dosing were 4.00 and 8.11 micro g/ml, 0.12 and 3.91 h, 13.88 and 16.53 h, and 122.7 and 112.9%, respectively, for the two models. The study showed that florfenicol was absorbed quickly and completely, distributed widely, and eliminated slowly in the infected pigs, and there was no statistically significant difference between the pharmacokinetic profiles for the infected and healthy pigs.

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.

Disposition kinetics of florfenicol in goats by using two analytical methods

Florfenicol, a monofluorinated analogue of thiamphenicol, has antibacterial activity against a broad spectrum of bacterial strains, including enteric bacteria that are resistant to chloramphenicol and thiamphenicol. The pharmacokinetics of florfenicol was studied following a single intravenous bolus or intramuscular injections at a dose of 20 mg/kg body weight, in five healthy goats. Serum florfenicol concentrations were determined using two analytical methods: microbiological assay and high-performance liquid chromatography (HPLC). Pharmacokinetic analysis was performed using redundant routine equations and the results derived from each method were compared. While florfenicol was detected for up to 4 and 8 h after administration by the bioassay, the drug was recovered in serum after 12 and 24 h by HPLC following intravenous and intramuscular injections, respectively. Comparison of the concentration profiles obtained by the two methods revealed substantial differences in the resultant kinetic data. Values for the initial serum concentration, elimination half-life, the area under the serum concentration-time curve, the mean residence time, and the systemic bioavailability were significantly (P < 0.01) higher when florfenicol concentrations were determined using HPLC. In conclusion, differences between analytical methodologies should be considered when interpreting the kinetic data for clinical use. However, both the hepatic biotransformations and the interchangeability of enantiomers need further investigation.

Serum and lung levels of thiamphenicol after administration of its glycinate N-acetylcysteinate ester in experimentally infected guinea pigs

Thiamphenicol is an analogue of chloramphenicol and is characterised by a broad spectrum of action. In this study, serum and lung levels of thiamphenicol (TAP) were studied in infected guinea pigs after the administration of thiamphenicol glycinate N-acetylcysteinate (TGA). Animals received a single dose of TGA (15 mg/kg, subcutaneously) immediately after intra-tracheal infection with Haemophilus influenzae (about 10(7) CFU/animal). Serum and lung concentrations of TAP were determined at 0, 1, 3, 6, 12 and 24 h after drug administration by means of HPLC. TAP serum levels were elevated at 1 h and remained detectable for 24 h after drug administration. Tissue lung levels were comparable to peak serum concentrations but remained higher and decreased more slowly than serum concentrations.

Efficacy of florfenicol for treatment of naturally occurring infectious bovine keratoconjunctivitis

OBJECTIVE

To determine the efficacy of florfenicol for treatment of calves with naturally occurring infectious bovine keratoconjunctivitis (IBK).

DESIGN

Randomized controlled field trial.

ANIMALS

63 beef calves and 80 dairy calves between 4 and 12 months of age.

PROCEDURE

Calves were randomly assigned to 1 of 3 treatment groups. Calves in the SC treatment group received a single dose of florfenicol (40 mg/kg [18.2 mg/lb of body weight), SC, on day 0. Calves in the IM treatment group received florfenicol (20 mg/kg [9.1 mg/lb]), IM, on days 0 and 2. Calves in the control group received injections of saline solution (0.9% NaCl), IM, on days 0 and 2. Calves were reevaluated every other day for 20 days after treatment.

RESULTS

Corneal ulcers healed by day 20 in 48 of 49 (98%) calves treated with florfenicol IM, 39 of 42 (93%) calves treated with florfenicol SC, and 33 of 52 (63%) control calves.

CONCLUSIONS AND CLINICAL RELEVANCE

Florfenicol administered SC (1 dose) or IM (2 doses 48 hours apart) was effective for treatment of calves with naturally occurring IBK.

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.

On-line microdialysis coupled with microbore liquid chromatography for the determination of unbound chloramphenicol and its glucuronide in rat blood

On-line microdialysis coupled with microbore liquid chromatography was used to investigate the pharmacokinetics of chloramphenicol and its glucuronide in rat blood. A microdialysis probe was inserted into a jugular vein of male Sprague-Dawley rats. Chloramphenicol succinate (20 mg/kg, intravenously) was then administered via a femoral vein. Dialysates were automatically injected onto a LC system, via an on-line injector. Samples were eluted with a mobile phase containing acetonitrile-10 mM monochloroacetic acid (30:70, v/v, pH 3.0). The UV detector wavelength was set at 278 nm. The limit of quantitation for chloramphenicol was 10 ng/ml. The in vitro recoveries of chloramphenicol and chloramphenicol glucuronide at 500 ng/ml were 32.2+/-0.3% and 11.4+/-0.7%, respectively (n = 6). Intra- and inter-assay accuracy and precision of the analyses were < or =10% in the range of 0.01 to 5.0 microg/ml.