Pharmacokinetic and pharmacodynamic modelling of marbofloxacin administered alone and in combination with tolfenamic acid in calves

Pharmacokinetic Characteristics of Tolfenamic Acid in Freshwater Crocodiles (Crocodylus siamensis)

The present study was undertaken to characterize the plasma kinetic disposition of tolfenamic acid (TA) in freshwater crocodiles. In total, 15 freshwater crocodiles were used in the experiment and randomly divided into three groups, with TA administered at 2 mg/kg body weight (b.w.) intravenously (IV) or at 2 or 4 mg/kg b.w. intramuscularly (IM). Blood samples were collected at predetermined times up to 168 h after IV or IM drug administration. Plasma concentrations of TA were determined using validated high-performance liquid chromatography with a UV detector and then analyzed based on the non-compartmental method. The maximum concentration values of TA were 3.03 µg/mL and 6.83 µg/mL following IM administration at a dose of 2 mg/kg b.w. or 4 mg/kg b.w., respectively. The elimination half-lives were 21.89 h (2 mg/kg; IV), 17.74 h (2 mg/kg; IM), and 13.57 h (4 mg/kg; IM). Following IV administration, the volume of distribution and clearance were 1.58 L/kg and 50.04 mL/h/kg, respectively. The absolute IM bioavailability was 71.0% at a dose of 2 mg/kg b.w. and 92.63% at a dose of 4 mg/kg b.w. The average ± SD of plasma protein binding of TA was 26.15 ± 4.93%. Good bioavailability levels and favorable plasma concentrations of TA were obtained in freshwater crocodiles after IM administrations, considering that this is the preferred route of drug administration in freshwater crocodiles. Multi-dose and pharmacodynamic studies are needed to better establish the safety and efficacy of using TA in this crocodilian species.

In silico approach towards polyphenols as targeting glucosamine-6-phosphate synthase for Candida albicans

Candida albicans is one of the most common species of fungus with life-threatening systemic infections and a high mortality rate. The outer cell wall layer of C. albicans is packed with mannoproteins and glycosylated polysaccharide moieties that play an essential role in the interaction with host cells and tissues. The glucosamine-6-phosphate synthase enzyme produces N-acetylglucosamine, which is a crucial chemical component of the cell wall of Candida albicans. Collectively, these components are essential to maintain the cell shape and for infection. So, its disruption can have serious effects on cell growth and morphology, resulting in cell death. Hence, it is considered a good antifungal target. In this study, we have performed an in silico approach to analyze the inhibitory potential of some polyphenols obtained from plants. Those can be considered important in targeting against the enzyme glucosamine-6-phosphate synthase (PDB-2VF5). The results of the study revealed that the binding affinity of complexes theaflavin and 3-o-malonylglucoside have significant docking scores and binding free energy followed by significant ADMET parameters that predict the drug-likeness property and toxicity of polyphenols as potential ligands. A molecular dynamic simulation was used to test the validity of the docking scores, and it showed that the complex remained stable during the period of the simulation, which ranged from 0 to 100 ns. Theaflavins and 3-o-malonylglucoside may be effective against Candida albicans using a computer-aided drug design methodology that will further enable researchers for future in vitro and in vivo studies, according to our in silico study.Communicated by Ramaswamy H. Sarma.

Quantitative Pharmacodynamic Characterization of Resistance versus Heteroresistance of Colistin in E. coli Using a Semimechanistic Modeling of Killing Curves

Heteroresistance corresponds to the presence, in a bacterial isolate, of an initial small subpopulation of bacteria characterized by a significant reduction in their sensitivity to a given antibiotic. Mechanisms of heteroresistance versus resistance are poorly understood. The aim of this study was to explore heteroresistance in mcr-positive and mcr-negative Escherichia coli strains exposed to colistin by use of modeling killing curves with a semimechanistic model. We quantify, for a range of phenotypically (susceptibility based on MIC) and genotypically (carriage of mcr-1 or mcr-3 or mcr-negative) different bacteria, a maximum killing rate (E_max) of colistin and the corresponding potency (EC₅₀), i.e., the colistin concentrations corresponding to E_max/2. Heteroresistant subpopulations were identified in both mcr-negative and mcr-positive E. coli as around 0.06% of the starting population. Minority heteroresistant bacteria, both for mcr-negative and mcr-positive strains, differed from the corresponding dominant populations only by the maximum killing rate of colistin (differences for E_max by a factor of 12.66 and 3.76 for mcr-negative and mcr-positive strains, respectively) and without alteration of their EC₅₀s. On the other hand, the resistant mcr-positive strains are distinguished from the mcr-negative strains by differences in their EC₅₀, which can reach a factor of 44 for their dominant population and 22 for their heteroresistant subpopulations. It is suggested that the underlying physiological mechanisms differ between resistance and heteroresistance, with resistance being linked to a decrease in the affinity of colistin for its site of action, whereas heteroresistance would, rather, be linked to an alteration of the target, which will be more difficult to be further changed or destroyed.

Experimental safety testing shows that the NSAID tolfenamic acid is not toxic to Gyps vultures in India at concentrations likely to be encountered in cattle carcasses

Population declines of Gyps vultures across the Indian subcontinent were caused by unintentional poisoning by the non-steroidal anti-inflammatory drug (NSAID) diclofenac. Subsequently, a number of other NSAIDs have been identified as toxic to vultures, while one, meloxicam, is safe at concentrations likely to be encountered by vultures in the wild. Other vulture-safe drugs need to be identified to reduce the use of those toxic to vultures. We report on safety-testing experiments on the NSAID tolfenamic acid on captive vultures of three Gyps species, all of which are susceptible to diclofenac poisoning. Firstly, we estimated the maximum level of exposure (MLE) of wild vultures and gave this dose to 40 Near Threatened Himalayan Griffons G. himalayensis by oral gavage, with 15 control birds dosed with benzyl alcohol (the carrier solution for tolfenamic acid). Two birds given tolfenamic acid died with elevated uric acid levels and severe visceral gout, while the remainder showed no adverse clinical or biochemical signs. Secondly, four G. himalayensis were fed tissues from water buffaloes which had been treated with double the recommended veterinary dose of tolfenamic acid prior to death and compared to two birds fed uncontaminated tissue; none suffered any clinical effects. Finally, two captive Critically Endangered vultures, one G. bengalensis and one G. indicus, were given the MLE dose by gavage and compared to two control birds; again, none suffered any clinical effects. The death of two G. himalayensis may have been an anomaly due to i) the high dose level used and ii) the high ambient temperatures at the time of the experiment. Tolfenamic acid is likely to be safe to Gyps vultures at concentrations encountered by wild birds and could therefore be promoted as a safe alternative to toxic NSAIDs. It is manufactured in the region, and is increasingly being used to treat livestock.

Role of the Abcg2 transporter in plasma levels and tissue accumulation of the anti-inflammatory tolfenamic acid in mice

The Breast Cancer Resistance Protein (BCRP/ABCG2) is an ATP-binding cassette efflux transporter that is expressed in the apical membrane of cells from relevant tissues involved in drug pharmacokinetics such as liver, intestine, kidney, testis, brain and mammary gland, among others. Tolfenamic acid is an anti-inflammatory drug used as an analgesic and antipyretic in humans and animals. Recently, tolfenamic acid has been repurposed as an antitumoral drug and for use in chronic human diseases such as Alzheimer. The aim of this work was to study whether tolfenamic acid is an in vitro Abcg2 substrate, and to investigate the potential role of Abcg2 in plasma exposure, secretion into milk and tissue accumulation of this drug. Using in vitro transepithelial assays with cells transduced with Abcg2, we showed that tolfenamic acid is an in vitro substrate of Abcg2. The in vivo effect of this transporter was tested using wild-type and Abcg2^-/- mice, showing that after oral and intravenous administration of tolfenamic acid, its area under the plasma concentration-time curve in Abcg2^-/- mice was between 1.7 and 1.8-fold higher compared to wild-type mice. Abcg2^-/- mice also showed higher liver and testis accumulation of tolfenamic acid after intravenous administration. In this study, we demonstrate that tolfenamic acid is transported in vitro by Abcg2 and that its plasma levels as well as its tissue distribution are affected by Abcg2, with potential pharmacological and toxicological consequences.

Implications for dosing regimen of enrofloxacin administered concurrently with dexamethasone in febrile buffalo calves

The objective of the study was to determine the influence of dexamethasone (DXM) on pharmacokinetics (PK) and pharmacodynamics (PD) of enrofloxacin (ENR) for dosage optimization following concurrent administration of ENR and DXM in febrile buffalo calves. A 2 μg/kg intravenous dosage of lipopolysaccharide derived from Escherichia coli was used to induce fever in calves. After inducing fever, ENR was administered at the dose rate of 12 mg/kg, IM followed by IM injection of DXM (0.05 mg/kg) in calves. Minor alterations in PK of ENR were observed following the administration of ENR + DXM. The PK parameters were t_1/2K₁₀ = 6.34 h, Cl/F = 0.729 L/kg/h, and MRT_0-∞ = 10.5 h. Antibacterial activity (MIC, MBC, ex vivo time-kill kinetics) of ENR for P. multocida was not affected by DXM. But MPC of ENR against P. multocida was lessened in presence of DXM. Using PK-PD-modeled AUC_0-24h/MIC values for bactericidal effect against P. multocida, daily dosages of ENR administered in combination with DXM were 4.02 mg/kg and 16.1 mg/kg, respectively, for MIC_90s of 0.125 μg/ml and 0.50 μg/ml. A dose of 5.38 mg/kg was determined for ENR for frequently occurring P. multocida infections having ≤ MIC₉₀ of 0.125 μg/ml and PK-PD modeled dose was comparable with the recommended ENR dose of 5 mg/kg for bovines for mild infections. It is suggested that a recommended dosage of 5-12.5 mg/kg of ENR can be used effectively in combination with DXM to treat P. multocida associated infections in buffalo calves without any risk of resistance amplification.

The effects of Mannheimia haemolytica and albendazole on marbofloxacin pharmacokinetics in lambs

The study aimed to define the effects of M. haemolytica and a single oral dose of albendazole on the single-dose pharmacokinetics of marbofloxacin in lambs. The pharmacokinetic-pharmacodynamic integration of marbofloxacin was applied to describe a 3 mg/kg intramuscular dose in lambs. The 6 healthy and 12 naturally infected with M. haemolytica lambs (Akkaraman, males weighing 10-15 kg and aged 2-3 months) were used in this study. In the marbofloxacin group, 6 healthy lambs received marbofloxacin. In the albendazole group after 2 weeks washout period, the same animals received marbofloxacin on 1 h after albendazole. In the diseased marbofloxacin group, 6 lambs naturally infected with M. haemolytica received marbofloxacin. In the diseased albendazole group, 6 lambs naturally infected with M. haemolytica received marbofloxacin on 1 h after albendazole. The marbofloxacin and albendazole were administered each as a single dose of 3 mg/kg intramuscular and 7.5 mg/kg oral, respectively, in the respective groups. Plasma concentration of marbofloxacin was measured with HPLC-UV and pharmacokinetic parameters were analyzed by non-compartmental model. Albendazole did not change the pharmacokinetic profiles of marbofloxacin in healthy and diseased lambs. However, M. haemolytica affected the pharmacokinetics of marbofloxacin in diseased lambs, AUC_0-24/MIC₉₀ ratio was not found to be higher than 125, but C_max/MIC₉₀ ratios was found to be higher than 10 for an MIC value of 0.25 μg/mL in all groups. The marbofloxacin dose described in this study may not be effective for the treatment of infections due to M. haemolytica in lambs, with MIC ≤ 0.25 μg/mL.

Pharmacokinetic-pharmacodynamic relationship of marbofloxacin for Escherichia coli and Pasturella multocida following repeated intramuscular administration in goats

The pharmacokinetics (PK) and pharmacodynamics (PD) of marbofloxacin (MBF) were determined in six healthy female goats of age 1.00-1.25 years after repeated administration of MBF. The MBF was administered intramuscularly (IM) at 2 mg kg^-1  day^-1 for 5 days. Plasma concentrations of MBF were determined by high-performance liquid chromatography, and PK parameters were obtained using noncompartmental analysis. The MBF concentrations peaked at 1 hr, and peak concentration (C_max ) was 1.760 µg/ml on day 1 and 1.817 µg/ml on day 5. Repeated dosing of MBF caused no significant change in PK parameters except area under curve (AUC) between day 1 (AUC_0-∞ D1 = 7.67 ± 0.719 µg × hr/ml) and day 5 (AUC_0-∞ D5 = 8.70 ± 0.857 µg × hr/ml). A slight difference in mean residence time between 1st and 5th day of administration and accumulation index (AI = 1.13 ± 0.017) suggested lack of drug accumulation following repeated IM administration up to 5 days. Minimum inhibitory concentration (MIC) demonstrated that Escherichia coli (MIC = 0.04 µg/ml) and Pasturella multocida (MIC = 0.05 µg/ml) were highly sensitive to MBF. Time-kill kinetics demonstrated rapid and concentration-dependent activity of MBF against these pathogens. PK/PD integration of data for E. coli and P. multocida, using efficacy indices: C_max /MIC and AUC_0-24hr /MIC, suggested that IM administration of MBF at a dose of 2 mg kg^-1  day^-1 is appropriate to treat infections caused by E. coli. However, a dose of 5 mg kg^-1  day^-1 is recommended to treat pneumonia caused by P. multocida in goats. The study indicated that MBF can be used repeatedly at dosage of 2 mg/kg in goats without risk of drug accumulation up to 5 days.

Differential susceptibility to tetracycline, oxytetracycline and doxycycline of the calf pathogens Mannheimia haemolytica and Pasteurella multocida in three growth media

For clinical isolates of bovine Mannheimia haemolytica and Pasteurella multocida, this study reports minimum inhibitory concentration (MIC) differences for tetracycline, oxytetracycline and doxycycline between cation-adjusted Mueller-Hinton broth (CAMHB), foetal bovine serum (FBS) and Roswell Park Memorial Institute (RPMI) medium. MICs were determined according to CLSI standards and additionally using five overlapping sets of twofold dilutions. Matrix effect: (a) free drug MICs and minimum bactericidal concentrations (MBC) for all drugs were significantly higher in FBS than in CAMHB for both pathogens (p < 0.001); (b) MICs and MBCs were higher for CAMHB and FBS compared to RPMI for P. multocida only. Net growth rate for P. multocida in CAMHB was significantly slower than in FBS and higher than in RPMI, correlating to MIC and MBC ranking. Drug effect: doxycycline MICs and MBCs were significantly lower (p < 0.001) in both CAMHB and FBS than tetracycline and oxytetracycline for both pathogens. Only for M. haemolytica were oxytetracycline MIC and MBC significantly lower than tetracycline, precluding the use of tetracycline to predict oxytetracycline susceptibility in this species. Determining potencies of tetracyclines in a physiological medium, such as FBS, is proposed, when the objective is correlation with pharmacokinetic data for dosage determination.

Optimal Regimens and Cutoff Evaluation of Tildipirosin Against Pasteurella multocida

Pasteurella multocida (PM) can invade the upper respiratory tract of the body and cause death and high morbidity. Tildipirosin, a new 16-membered-ring macrolide antimicrobial, has been recommended for the treatment of respiratory diseases. The objective of this research was to improve the dose regimes of tildipirosin to PM for reducing the macrolides resistance development with the pharmacokinetic/pharmacodynamic (PK/PD) modeling approach and to establish an alternate cutoff for tildipirosin against PM. A single dose (4 mg/kg body weight) of tildipirosin was administered via intramuscular (i.m.) and intravenous (i.v.) injection to the pigs. The minimum inhibitory concentration (MIC) values of clinical isolates (112) were measured in the range of 0.0625–32 μg/ml, and the MIC₅₀ and MIC₉₀ values were 0.5 and 2 μg/ml, respectively. The MIC of the selected PM04 was 2 and 0.5 μg/ml in the tryptic soy broth (TSB) and serum, respectively. The main pharmacokinetic (PK) parameters including the area under the curve at 24 h (AUC_{24 h}), AUC, terminal half-life (T_1/2), the time to peak concentration (T_max), peak concentration (C_max), relative total systemic clearance (CL_b), and the last mean residence time (MRT_last) were calculated to be 7.10, 7.94 μg^∗h/ml, 24.02, NA h, NA μg/ml, 0.46 L/h^∗kg, 8.06 h and 3.94, 6.79 μg^∗h/ml, 44.04, 0.25 h, 0.98 μg/ml, 0.43 L/h^∗kg, 22.85 h after i.v. and i.m. induction, respectively. Moreover, the bioavailability of i.m. route was 85.5%, and the unbinding of tildipirosin to serum protein was 78%. The parameters AUC_{24 h}/MIC in serum for bacteriostatic, bactericidal, and elimination activities were calculated as 18.91, 29.13, and 34.03 h based on the inhibitory sigmoid E_max modeling. According to the Monte Carlo simulation, the optimum doses for bacteriostatic, bactericidal, and elimination activities were 6.10, 9.41, and 10.96 mg/kg for 50% target and 7.86, 12.17, and 14.57 mg/kg for 90% target, respectively. The epidemiological cutoff value (ECV) was calculated to be 4 μg/ml which could cover 95% wild-type clinical isolates distribution. The PK-PD cutoff (CO_PD) was analyzed to be 0.25 μg/ml in vitro for tildipirosin against PM based on the Monte Carlo simulation. Compared with these two cutoff values, the finial susceptible breakpoint was defined as 4 μg/ml. The data presented now provides the optimal regimens (12.17 mg/kg) and susceptible breakpoint (4 μg/ml) for clinical use, but these predicted data should be validated in the clinical practice.

Pharmacokinetic/pharmacodynamic relationship of enrofloxacin against Aeromonas hydrophila in crucian carp (Carassius auratus gibelio)

The pharmacokinetic (PK) properties of enrofloxacin (ENR) and its metabolite ciprofloxacin (CIP) were investigated in crucian carp following oral administration at different dose levels (5, 10, 20, 40 mg/kg body weight). The disposition kinetics of ENR was found to be linear over the dose range studied. Serum half-lives ranged from 64.56 to 72.68 hr. The in vitro and ex vivo activities of ENR in serum against a pathogenic strain of Aeromonas hydrophila were determined. In vitro and ex vivo bactericidal activity of ENR was concentration dependent. Dosing of 10 mg/kg resulted in an AUC/minimum inhibitory concentration (MIC) ratio of 368.92 hr and a C_max /MIC ratio of 7.23, respectively, against A. hydrophila 147 (MIC = 0.48 μg/ml), indicating a likely high level of effectiveness in clinical infections caused by A. hydrophila with MIC value ≤ 0.48 μg/ml. Modeling of ex vivo growth inhibition data to the sigmoid Emax equation provided the values of AUC_24 hr /MIC required to produce bacteriostasis, bactericidal activity, and elimination of bacteria, these values were 21.70, 53.01, and 125.21 hr, respectively. These findings in conjunction with MIC₉₀ data suggested that ENR at the dose of 7.81 mg/kg predicted a positive clinical outcome and minimize the risk of emergence of resistance.

Evaluation of Marbofloxacin in Beagle Dogs After Oral Dosing: Preclinical Safety Evaluation and Comparative Pharmacokinetics of Two Different Tablets

The current study evaluates a tested marbofloxacin tablet (MBT) (Petsen), in terms of bioavailability and pharmacokinetics (PK) in a comparison of the commercialized and standard tablet (Marbocyl) in beagle dogs. Four different bacterial species were selected for the determination of the minimal inhibitory concentration (MIC) against marbofloxacin (MBF). Target animal safety studies were conducted with a wide spectrum of dosages of Petsen. Pharmacokinetics and bioavailability of Petsen were observed after the oral administration of a recommended dosage of 2 mg/kg. The MIC₉₀ of MBF against Staphylococcus aureus, Escherichia coli, Pasteurella multocida, and Streptococcus were 2.00, 4.00, 0.25, and 0.50 μg/ml, respectively. These results showed that the MBT has an expected antimicrobial activity in vitro. The main parameters of t_1/2β, Cl_b, AUC_0−∞, C_max, and K_e were 22.14 h, 0.15 L/h, 13.27 μg.h/ml, 0.95 μg/ml, 0.09 h⁻¹, and 16.47 h, 0.14 L/h, 14.10 μg.h/ml, 0.97 μg/ml, 0.11 h⁻¹ after the orally administrated Petsen and Marbocyl, while no biologically significant changes and toxicological significance have been found by their comparison. These findings indicate that the Petsen had a slow elimination, high bioavailability and kinetically similar to the commercialized Marbocyl. Furthermore, no statistically significant differences were distinguished on the continuous gradient dosages of 2, 6, and 10 mg/kg in the term of the clinical presentation. The present study results displayed that the tested MBT (Petsen) was safe, with limited toxicity, which was similar to the commercialized tablet (Marbocyl), could provide an alternative MBT as a veterinary medicine in beagle dogs.

Tolfenamic Acid

Tolfenamic acid (TA) is a nonsteroidal antiinflammatory drug and belongs to the group of fenamates. It is used as a potent pain reliever in the treatment of acute migraine attacks, and disorders like dysmenorrhea, rheumatoid, and osteoarthritis. TA has shown excellent in vitro antibacterial activity against certain ATCC strains of bacteria when complexed with bismuth(III). It has also been reported to block pathological processes associated with Alzheimer's disease. In the recent past, TA has also been used as a novel anticancer agent for the treatment of various cancers. In view of the clinical importance of TA, a comprehensive review of the physical and pharmaceutical properties and details of the various analytical methods used for the assay of the drug in pharmaceutical and biological systems has been made. The methods reviewed include identification tests and titrimetric, spectrophotometric, chromatographic, electrochemical, thermal, microscopic, enzymatic, and solid-state techniques. Along with the analytical profile, the stability and degradation of TA, its pharmacology and pharmacokinetics, dosage forms and dose, adverse effects and toxicity, and interactions have been discussed.

Pharmacokinetic/pharmacodynamic assessment of cefquinome against Actinobacillus Pleuropneumoniae in a piglet tissue cage infection model

To evaluate the relationship between the pharmacokinetic/pharmacodynamic (PK/PD) parameters and the antibacterial effect of cefquinome against Actinobacillus pleuropneumoniae, a tissue cage infection model was established in piglets. In this model, an initial count of A. pleuropneumoniae of approximately 10⁶ CFU/mL was exposed to different concentrations of cefquinome after multiple administration at dosages of 0.2, 0.4, 0.8, 1, 2, 4 mg/kg body weight once a day for 3 days. Concentration of cefquinome and bacterial numbers of A. pleuropneumoniae in the tissue-cage fluid (TCF) were monitered. An inhibitory form of sigmoid maximum effect (E_max) model was used to estimate the relationship between the antibacterial effect and PK/PD indices of cefquinome against A. pleuropneumoniae. The minimum inhibitory concentration of cefquinome against A. pleuropneumoniae was 0.016 μg/mL in TCF. The total maximum antibacterial effect was a 3.96 log₁₀ (CFU/mL) reduction. In addition, the cumulative percentage of time over a 24 h period that the drug concentration exceeds the MIC (%T > MIC) was the pharmacokinetic-pharmacodynamic (PK-PD) index that best correlated with the antibacterial efficacy (R² = 0.967). The estimated %T > MIC values were 11.59, 27.49, and 59.81% for a 1/3-log₁₀ (CFU/mL) reduction, a 2/3-log₁₀ (CFU/mL) reduction, and a 1-log₁₀ (CFU/mL) reduction, respectively, during the 24h administration period of cefquinome. In conclusion, cefquinome exhibits excellent antibacterial activity and time-dependent characteristics against A. pleuropneumoniae in vivo. Furthermore, these data provide meaningful guidance to optimize regimens of cefquinome to treat respiratory tract infections caused by A. pleuropneumoniae.

Implementing Precision Antimicrobial Therapy for the Treatment of Bovine Respiratory Disease: Current Limitations and Perspectives

The therapeutic efficacy of an early treatment protocol with an infection-stage adjusted fluoroquinolone regimen was evaluated in a field study on young bulls (YBs) presenting signs of bovine respiratory disease (BRD). A total of 195 YB (Charolais, Limousin, and Rouge-des-Prés breeds) from 6 farms implementing or not prophylactic antimicrobial treatments (PROPHY or absence) were randomly assigned to 1 of 2 experiment groups based on time of detection of BRD and first-line marbofloxacin regimen, early adjusted dose [Early 2 (E2)] or late standard dose [Late 10 (L10)]. Each YB was administered orally a reticulo-rumen bolus, allowing continuous monitoring of ruminal temperature. In the E2 group, YB presenting early signs of BRD, i.e., an increase in ruminal temperature over 40.2°C and persisting more than 12 h, confirmed by a clinical examination showing no or mild signs of BRD, were given 2 mg/kg of marbofloxacin. In the L10 group, YBs presenting moderate or severe signs of BRD at visual inspection, confirmed at clinical examination, were given 10 mg/kg of marbofloxacin. If needed, YBs were given a relapse treatment. The YBs were followed for 30 days. The proportions of first and relapse treatments were calculated, as well as the therapeutic efficacy at day 10. In the E2 group, the first-line treatments’ proportion was significantly higher (P < 0.05), while the relapse treatments’ proportion tended to be higher (P = 0.08), than in the L10 group. Evolution of clinical scores (CSs) of diseased YB was followed for 10 days. In both groups, CS and rectal temperature decreased significantly 24 h after treatment (P < 0.05). Treatment incidences (TI) representing antimicrobial consumption assessed on used daily doses (UDD) were calculated. Antimicrobial consumption of marbofloxacin and relapse treatments were not significantly different between the groups. These values were strongly influenced by the recourse to a prophylactic antimicrobial treatment, accounting for more than 90% of the antimicrobial amount in the herds implementing prophylaxis. The higher number of treatments in the groups treated on the basis of ruminal temperature monitoring, the accuracy of the detection method, and the necessary conditions to implement precision antimicrobial therapy in the field are discussed in this article.

Pharmacokinetic-Pharmacodynamic Modeling of Enrofloxacin Against Escherichia coli in Broilers

The purpose of the present study was to establish a pharmacokinetic/pharmacodynamic (PK/PD) modeling approach for the dosage schedule design and decreasing the emergence of drug-resistant bacteria. The minimal inhibitory concentration (MIC) of 929 Escherichia coli isolates from broilers to enrofloxacin and ciprofloxacin was determined following CLSI guidance. The MIC50 was calculated as the populational PD parameter for enrofloxacin against E. coli in broilers. The 101 E. coli strains with MIC closest to the MIC50 (0.05 μg/mL) were submitted for serotype identification. The 13 E. coli strains with O and K serotype were further utilized for determining pathogencity in mice. Of all the strains tested, the E. coli designated strain Anhui 112 was selected for establishing the disease model and PK/PD study. The PKs of enrofloxacin after oral administration at the dose of 10 mg/kg body weights (BW) in healthy and infected broilers was evaluated with high-performance liquid chromatography (HPLC) method. For intestinal contents after oral administration, the peak concentration (C max), the time when the maximum concentration reached (T max), and the area under the concentration-time curve (AUC) were 21.69-31.69 μg/mL, 1.13-1.23 h, and 228.97-444.86 μg h/mL, respectively. The MIC and minimal bactericidal concentration (MBC) of enrofloxacin against E. coli (Anhui 112) in Mueller-Hinton (MH) broth and intestinal contents were determined to be similar, 0.25 and 0.5 μg/mL respectively. In this study, the sum of concentrations of enrofloxacin and its metabolite (ciprofloxacin) was used for the PK/PD integration and modeling. The ex vivo growth inhibition data were fitted to the sigmoid E max (Hill) equation to provide values for intestinal contents of 24 h area under concentration-time curve/MIC ratios (AUC0-24 h/MIC) producing, bacteriostasis (624.94 h), bactericidal activity (1065.93 h) and bacterial eradication (1343.81 h). PK/PD modeling was established to simulate the efficacy of enrofloxacin for different dosage regimens. By model validation, the protection rate was 83.3%, demonstrating that the dosage regimen of 11.9 mg/kg BW every 24 h during 3 days provided great therapeutic significance. In summary, the purpose of the present study was to first design a dosage regimen for the treatment E. coli in broilers by enrofloxacin using PK/PD integrate model and confirm that this dosage regimen presents less risk for emergence of floroquinolone resistance.

Response of a clinical Escherichia coli strain to repeated cefquinome exposure in a piglet tissue-cage model

BACKGROUND

In order to provide some basis for effective dosage regimens that optimize efficacy with respect to bacteriological and clinical cures, the in vivo activity of cefquinome against a clinical Escherichia coli (E.coli) strain (the minimum inhibitory concentration value for this strain equals to the MIC90 value of 0.25 μg/ml for 210 E.coli strains isolated from pigs) was investigated by using a piglet tissue-cage infection model. The aim was to elucidate the pharmacokinetic/pharmacodynamics (PK/PD) index associated with cefquinome efficacy, and then to identify the magnitude of the PK/PD parameter required for different degree of efficacy in clinical treatment.

RESULTS

Tissue-cage infection model was established in piglets, and then the animals received intramuscular injection of cefquinome twice a day for 3 days to create a range of different drug exposures. The tissue-cage fluid was collected at 1, 3, 6, 9 and 12 h after every drug administration for drug concentrationdetermination and bacteria counting. Different cefquinome regimens produced different percentages of time during that drug concentrations exceeded the MIC (%T > MIC), ranging from 0% to 100%. Cefquinome administration at 0.2, 0.4, 0.6, 0.8, 1, 2 and 4 mg/kg reduced the bacterial count (log10 CFU/mL) in tissue-cage fluid by -1.00 ± 0.32, -1.83 ± 0.08, -2.33 ± 0.04, -2.96 ± 0.16, -2.99 ± 0.16, -2.93 ± 0.11, -3.43 ± 0.18, respectively. The correlation coefficient of the PK/PD index with antibacterial effect of the drug was 0.90 for %T > MIC, 0.62 for AUC0-12/MIC, and 0.61 for Cmax/MIC, suggesting the most important PK/PD parameter was %T > MIC. A inhibitory form of sigmoid maximum effect (Emax) model was used to estimate %T > MIC, and the respective values required for continuous 1/6-log drop, 1/3-log drop and 1/2-log drop of the clinical E.coli count during each 12 h treatment period were 3.97%, 17.08% and 52.68%.

CONCLUSIONS

The data derived from this study showed that cefquinome exhibited time-dependent killing profile. And from the results of the present study, it can be assumed that when %T > MIC reached 52.68%, cefquinome could be expected to be effective against a clinical E.coli strain for which the MIC value is below 0.128 μg/ml (3-log drop of bacteria count can be achieved after six successive administrations for 3 days).

In vivo antimicrobial activity of marbofloxacin against Pasteurella multocida in a tissue cage model in calves

Marbofloxacin is a fluoroquinolone specially developed for use in veterinary medicine with broad-spectrum antibacterial activity. The objective of our study was to re-evaluate in vivo antimicrobial activity of marbofloxacin against Pasteurella multocida using subcutaneously implanted tissue cages in calves. Calves were infected by direct injection into tissue cages with P. multocida(type B, serotype 2), then intramuscularly received a range of marbofloxacin doses 24 h after inoculation. The ratio of 24 h area under the concentration-time curve divided by the minimum inhibitory concentration or the mutant prevention concentration (AUC24 h/MIC or AUC24 h/MPC) was the pharmacokinetic-pharmacodynamic (PK/PD) index that best described the effectiveness of marbofloxacin against P. multocida (R (2) = 0.8514) by non-linear regression analysis. Marbofloxacin exhibited a good antimicrobial activity in vivo. The levels of AUC24 h/MIC and AUC24 h/MPC that produced 50% (1.5log10 CFU/mL reduction) and 90% (3log10 CFU/mL reduction) of maximum response were 18.60 and 50.65 h, 4.67 and 12.89 h by using sigmoid Emax model WINNONLIN software, respectively. The in vivo PK/PD integrated methods by tissue cage model display the advantage of the evaluation of antimicrobial activity and the optimization of the dosage regimen for antibiotics in the presence of the host defenses, especially in target animal of veterinary interest.

Mutant prevention concentration, pharmacokinetic-pharmacodynamic integration, and modeling of enrofloxacin data established in diseased buffalo calves

The pharmacokinetic-pharmacodynamic (PK/PD) modeling of enrofloxacin data using mutant prevention concentration (MPC) of enrofloxacin was conducted in febrile buffalo calves to optimize dosage regimen and to prevent the emergence of antimicrobial resistance. The serum peak concentration (Cmax ), terminal half-life (t1/2 K10) , apparent volume of distribution (Vd(area) /F), and mean residence time (MRT) of enrofloxacin were 1.40 ± 0.27 μg/mL, 7.96 ± 0.86 h, 7.74 ± 1.26 L/kg, and 11.57 ± 1.01 h, respectively, following drug administration at dosage 12 mg/kg by intramuscular route. The minimum inhibitory concentration (MIC), minimum bactericidal concentration, and MPC of enrofloxacin against Pasteurella multocida were 0.055, 0.060, and 1.45 μg/mL, respectively. Modeling of ex vivo growth inhibition data to the sigmoid Emax equation provided AUC24 h /MIC values to produce effects of bacteriostatic (33 h), bactericidal (39 h), and bacterial eradication (41 h). The estimated daily dosage of enrofloxacin in febrile buffalo calves was 3.5 and 8.4 mg/kg against P. multocida/pathogens having MIC90 ≤0.125 and 0.30 μg/mL, respectively, based on the determined AUC24 h /MIC values by modeling PK/PD data. The lipopolysaccharide-induced fever had no direct effect on the antibacterial activity of the enrofloxacin and alterations in PK of the drug, and its metabolite will be beneficial for its use to treat infectious diseases caused by sensitive pathogens in buffalo species. In addition, in vitro MPC data in conjunction with in vivo PK data indicated that clinically it would be easier to eradicate less susceptible strains of P. multocida in diseased calves.

Comparison of pharmacokinetics of marbofloxacin after subcutaneous administration of various multiple-dose regimens to water buffalo calves (Bubalus bubalis)

OBJECTIVE

To determine pharmacokinetics of marbofloxacin in water buffalo calves (Bubalus bubalis) after multiple SC administrations and to assess differences in regimen efficacy.

ANIMALS

18 healthy buffalo calves.

PROCEDURES

Calves (n = 6 calves/group) were assigned to receive marbofloxacin SC in the neck at 1 of 3 dosages (2 mg/kg, q 24 h for 6 days [regimen 1]; 4 mg/kg, q 48 h for 6 days [regimen 2]; and 4 mg/kg, q 24 h for 3 days [regimen 3]). Serum marbofloxacin concentrations were analyzed. Efficacy predictors were estimated on the basis of minimum inhibitory concentration and mutant prevention concentration reported for Pasteurella multocida and Mannheimia haemolytica.

RESULTS

Mean ± SD area under the concentration-time curve was 5.92 ± 0.40 μg•h/mL for regimen 1, which differed significantly from that for regimens 2 (14.26 ± 0.92 μg•h/mL) and 3 (14.17 ± 0.51 μg•h/mL). Mean residence time and mean elimination half-life for regimen 2 (9.93 ± 0.20 hours and 8.77 ± 0.71 hours) both differed significantly from those for regimens 1 (721 ± 0.11 hours and 5.71 ± 0.38 hours) and 3 (759 ± 0.13 hours and 737 ± 1.19 hours). Values obtained from indices for P multocida and M haemolytica had an excessively wide range because of the various degrees of antimicrobial susceptibility (low, medium, and high) of the strains.

CONCLUSIONS AND CLINICAL RELEVANCE

Regimen 3 had the most favorable indices, and it would be conducive for owner compliance and require less handling of animals.

Pharmacokinetic/pharmacodynamic relationship of marbofloxacin against Pasteurella multocida in a tissue-cage model in yellow cattle

The fluoroquinolone antimicrobial drug marbofloxacin was administered to yellow cattle intravenously and intramuscularly at a dose of 2 mg/kg of body weight in a two-period crossover study. The pharmacokinetic properties of marbofloxacin in serum, inflamed tissue-cage fluid (exudate), and noninflamed tissue-cage fluid (transudate) were studied by using a tissue-cage model. The in vitro and ex vivo activities of marbofloxacin in serum, exudate, and transudate against a pathogenic strain of Pasteurella multocida (P. multocida) were determined. Integration of in vivo pharmacokinetic data with the in vitro MIC provided mean values for the area under the curve (AUC)/MIC for serum, exudate, and transudate of 155.75, 153.00, and 138.88, respectively, after intravenous dosing and 160.50, 151.00, and 137.63, respectively, after intramuscular dosing. After intramuscular dosing, the maximum concentration/MIC ratios for serum, exudate, and transudate were 21.13, 9.13, and 8.38, respectively. The ex vivo growth inhibition data after intramuscular dosing were fitted to the inhibitory sigmoid Emax equation to provide the values of AUC/MIC required to produce bacteriostasis, bactericidal activity, and elimination of bacteria. The respective values for serum were 17.25, 31.29, and 109.62, and slightly lower values were obtained for transudate and exudate. It is proposed that these findings might be used with MIC50 or MIC90 data to provide a rational approach to the design of dosage schedules which optimize efficacy in respect of bacteriological as well as clinical cures.

Comparative mutant prevention concentration and antibacterial activity of fluoroquinolones against Escherichia coli in diarrheic buffalo calves

Owing to emerging threat of antimicrobial resistance, mutant prevention concentration (MPC) is considered as an important parameter to evaluate the antimicrobials for their capacity to restrict/allow the emergence of resistant mutants. Therefore, MPCs of ciprofloxacin, enrofloxacin, levofloxacin, moxifloxacin, and norfloxacin were determined against Escherichia coli isolates of diarrheic buffalo calves. The minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) were also established. The MICs of ciprofloxacin, enrofloxacin, levofloxacin, moxifloxacin and norfloxacin were 0·009, 0·022, 0·024, 0·028, and 0·036 μg/ml, respectively. The MBCs obtained were very close to the MICs of respective drugs that suggested a bactericidal mode of action of antimicrobials. The MPCs (μg/ml) of ciprofloxacin (4·2×MIC), moxifloxacin (4·8×MIC), and norfloxacin (5·1×MIC) were approximately equal but slightly lower than enrofloxacin (7·6×MIC) and levofloxacin (8·5×MIC) against clinical isolates of E. coli. The MPC data suggested that enrofloxacin has the potential for restricting the selection of E. coli mutants during treatment at appropriate dosing.

Pharmacokinetic and pharmacodynamic testing of marbofloxacin administered as a single injection for the treatment of bovine respiratory disease

New approaches in Pharmacokinetic/Pharmacodynamic (PK/PD) integration suggested that marbofloxacin, a fluoroquinolone already licensed for the treatment of bovine respiratory disease at a daily dosage of 2 mg/kg for 3-5 days, would be equally clinically effective at 10 mg/kg once (Forcyl(®)), whilst also reducing the risk of resistance. This marbofloxacin dosage regimen was studied using mutant prevention concentration (MPC), PK simulation, PK/PD integration and an in vitro dynamic system. This system simulated the concentration-time profile of marbofloxacin in bovine plasma established in vivo after a single 10 mg/kg intramuscular dose and killing curves of field isolated Pasteurellaceae strains of high (minimum inhibitory concentration (MIC) MIC ≤ 0.03 μg/mL), average (MIC of 0.12-0.25 μg/mL) and low (MIC of 1 μg/mL) susceptibility to marbofloxacin. The marbofloxacin MPC values were 2- to 4-fold the MIC values for all Mannheimia haemolytica, Pasteurella multocida tested. Marbofloxacin demonstrated a concentration-dependent killing profile with bactericidal activity observed within 1 h for most strains. No resistance development (MIC ≥ 4 μg/mL) was detected in the dynamic tests. Target values for risk of resistance PK/PD surrogates (area under the curve (AUC) AUC(24 h) /MPC and T(>MPC) /T(MSW) ratio) were achieved for all clinically susceptible pathogens. The new proposed dosing regimen was validated in vitro and by PK/PD integration confirming the single-injection short-acting antibiotic concept.

Survey of marbofloxacin susceptibility of bacteria isolated from cattle with respiratory disease and mastitis in Europe

A monitoring programme conducted in Europe since 1994 to survey the marbofloxacin susceptibility of bacterial pathogens isolated from cattle has established the susceptibility of bacterial strains isolated before any antibiotic treatment from bovine mastitis and bovine respiratory disease (BRD) cases between 2002 and 2008. Minimum inhibitory concentration (MIC) was determined by a standardised microdilution technique. For respiratory pathogens, Pasteurella multocida and Mannheimia haemolytica isolates (751 and 514 strains, respectively) were highly susceptible to marbofloxacin (MIC≤0.03 µg/ml for 77.39 per cent of the strains) and only 1.75 per cent of M haemolytica strains were resistant (MIC≥4 µg/ml). Histophilus somni isolates (73 strains) were highly susceptible to marbofloxacin (0.008 to 0.06 µg/ml). Mycoplasma bovis MIC (171 strains) ranged from 0.5 to 4 µg/ml. For mastitis pathogens, the majority of Escherichia coli isolates were highly susceptible to marbofloxacin (95.8 per cent of 617 strains). Staphylococcus aureus and coagulase-negative staphylococci (568 and 280 strains) had a homogenous population with MIC centred on 0.25 µg/ml. Streptococcus uberis and Streptococcus dysgalactiae (660 and 217 strains) were moderately susceptible with MIC centred on 1 µg/ml. Marbofloxacin MIC for these various pathogens appeared stable over the seven years of the monitoring programme and was similar to previously published MIC results.