Pharmacokinetics and lung tissue concentrations of tulathromycin in swine

Comparison of the Minimum Inhibitory and Mutant Prevention Drug Concentrations for Pradofloxacin and 7 Other Antimicrobial Agents Tested Against Swine Isolates of Actinobacillus pleuropneumoniae and Pasteurella multocida

Pradofloxacin is a dual targeting, bactericidal fluoroquinolone recently approved for treating bacteria causing swine respiratory disease. Currently, an abundance of in vitro data does not exist for pradofloxacin. We determined the minimum inhibitory concentration (MIC) and mutant prevention concentrations (MPC) of pradofloxacin compared to ceftiofur, enrofloxacin, florfenicol, marbofloxacin, tildipirosin, tilmicosin and tulathromycin against swine isolates of Actinobacillus pleuropneumoniae and Pasteurella multocida. Overall, pradofloxacin had the lowest MIC and MPC values as compared to the other agents tested. For example, pradofloxacin MIC values for 50%, 90% and 100% of A. pleuropneumoniae strains were ≤0.016 µg/mL, ≤0.016 µg/mL and ≤0.016 µg/mL and for P. multocida were ≤0.016 µg/mL, ≤0.016 µg/mL and 0.031 µg/mL, respectively. The MPC values for 50%, 90% and 100% of A. pleuropneumoniae strains were 0.031 µg/mL, 0.063 µg/mL and 0.125 µg/mL and for P. multocida were ≤0.016 µg/mL, 0.031 µg/mL and 0.0.063 µg/mL, respectively. By MPC testing, all strains were at or below the susceptibility breakpoint. Based on MPC testing, pradofloxacin appears to have a low likelihood for resistance selection. This study represents the most comprehensive in vitro comparison of the above noted drugs and the first report for pradofloxacin and tildipirosin.

Eco-conscious potentiometric sensing: a multiwalled carbon nanotube-based platform for tulathromycin monitoring in livestock products

Tulathromycin (TUL) is a widely used veterinary antibiotic for treating bovine and porcine respiratory infections. Consuming animal-derived food contaminated with this medication may jeopardize human health. This work adopted the first portable potentiometric platform for direct TUL sensing in pharmaceutical and food products. The sensor employed a plasticized PVC membrane on a glassy carbon electrode doped with calix[6]arene and multi-walled carbon nanotubes (MWCNT) in a single solid contact layer for selective binding and signal stability. Characterization via scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) confirmed the material's integrity. The MWCNT-based sensor produced a stable Nernstian response (1.0 × 10-7 to 1.0 × 10-3 M) and a limit of detection (LOD) of 9.76 × 10-8 M with instantaneous response (8 ± 2 s). IUPAC validation revealed high selectivity for TUL against interfering ions, minimal drift (0.6 mV/h), and functionality over a broad pH range (2.0-7.0), allowing direct application to dosage form, spiked milk, and liver samples. Eco-Scale, AGREE, and Whiteness assessment proved the method's ecological sustainability, economic viability, and practical feasibility, surpassing traditional approaches.

Susceptibility evaluation and PK/PD integration of tulathromycin against Actinobacillus pleuropneumoniae during the mutant selection window

Introduction

Actinobacillus pleuropneumoniae (APP) is a serious pathogen that affects the development of livestock breeding. Due to excessive use of antimicrobial drugs, many multidrug-resistant bacteria have emerged and spread, which have threatened the livestock industry. Therefore, we established a peristaltic pump infection model (PPIM) to evaluate the susceptibility change and pharmacokinetic/pharmacodynamic (PK/PD) integration of tulathromycin against APP during the mutant selection window (MSW) for preventing the emergence of mutant-resistant bacteria.

Methods

The 99% minimum inhibitory concentration (MIC99) and mutant prevention concentration (MPC) of tulathromycin against APP were measured using the agar-plate method. After the model of dynamic infection had been established based on tulathromycin data in lungs, different dosages were administered to make the drug concentrations located in different parts of the MSW. The population and sensitivity of APP were monitored. Tulathromycin concentrations were measured by high-performance liquid chromatography-tandem mass spectrometry. Finally, a sigmoid Emax model was used to analyze the relationships between PK/PD parameters and antibacterial effects.

Results and discussion

The values of MIC, MIC99, and MPC of tulathromycin against APP were 2, 1.4, and 44.8 μg/mL, respectively. The PPIM was stable. An elimination effect without regrowth was observed at 5.6 to 44.8 μg/mL (-4.48 to -7.05 Log10 CFU/mL, respectively). The MIC of APP increased 32-fold at 8 MIC99. AUC168 h/MIC99 had the best fit with the antibacterial effect (R 2 = 0.9867). The AUC168 h/MIC99 required to achieve bacteriostatic, bactericidal, and clearance effects were 1.80, 87.42, and 198 h, respectively. Our results could provide guidance for the clinical application of tulathromycin to treat APP infection and avoid the generation of drug-resistant bacteria.

Determination of lekethromycin in plasma and tissues of pneumonia-infected rats by ultra-high performance liquid chromatography-tandem mass spectrometry

Lekethromycin (LKMS), a novel semi-synthetic macrolide lactone, had the characteristics of high plasma protein binding rate, fast absorption, slow elimination, and wide distribution in rat pharmacokinetics studies. A reliable analytical ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS)-based method was established by using tulathromycin and TLM (CP-60, 300) as internal standards for detection of LKMS and LKMS-HA, respectively. Samples preparation and UPLC-MS/MS conditions were optimized for complete and accurate quantification. Tissue samples were extracted with 1% formic acid in acetonitrile and purified by PCX cartridges. According to FDA and EMA guidelines for bioanalytical method, several rat characteristic tissues were selected for method validation, such as muscle, lung, spleen, liver, kidney, and intestines. The transitions m/z 402.900 > 158.300, m/z 577.372 > 158.309, m/z 404.200 > 158.200, and m/z 577.372 > 116.253 were monitored and quantified for LKMS, LKMS-HA, tulathromycin and TLM, respectively. According to the ratio with IS peak aera, the accuracy and precision of LKMS were 84.31%-112.50% with RSD 0.93%-9.79% and LKMS-HA were 84.62%-103.96% with RSD 0.73%-10.69%, and the method had been established and complied with FDA, EU, and Japanese guidelines. Finally, this method was applied to detect LKMS and LKMS-HA in plasma and tissues of pneumonia-infected rats that were intramuscularly administered and treated with LKMS intramuscular injection of 5 mg/kg BW and 10 mg/kg BW, and the characteristics of pharmacokinetics and tissue distribution were compared with normal rats.

Tulathromycin – a semi-synthetic macrolidе antibiotic. I. Characteristics and antibacterial activity

This article reviews the available literature on the characteristics and antimicrobial activity of the semi-synthetic macrolide antibiotic tulathromycin from the triamilides subclass. The product has a high activity against Gram-negative respiratory pathogens and desirable pharmacological characteristics for high and persistent tissue levels in domestic animals. Representatives of the macrolide and lincosamide group are investigated and the similarities and differences from tulathromycin are outlined. It is emphasised that at the background of increasing bacterial resistance to a number of antimicrobial agents, only few tulathromycin-resistant strains of P. multocida and M. haemolytica have been reported so far. Tulathromycin is considered highly effective against common bacterial agents of respiratory diseases in large ruminants, pigs and sheeps, and may be an alternative for control of resistant bacterial pathogens

Tulathromycin – a semi-synthetic macrolidе antibiotic. II. Usage in veterinary medicine

This article presents the results of studies on the use of the new macrolide antibiotic tulathromycin in veterinary medicine. The information is presented according to the species of domestic animals, diseases, doses and shemes for therapy and metaphylaxis. The first section includes data for cattle and calves affected by respiratory diseases, caused by M. haemolytica, M. bovis, H. somni and P. multocida, and keratoconjunctivitis caused by M. bovis. The second one shows data for swine and pigs affected by the respiratory pathogens A. pleuropneumoniae, P. multocida, H. parasuis, B. bronhiseptica and M. hyopneumoniae. A third group presents information about small ruminants with manifested respiratory diseases caused by M. haemolytica, P. multocida, Mycoplasma spp., Pseudomonas spp. and hoof diseases from Dehelobacter nodosus. Fourth group includes the first test results of Rhodococcus equi, Streptococcus zooepidemicus, Theileria equi, Babesia bovis and Babesia bigemina, causing diseases in horses. The fifth section includes reports of treated rabbits most commonly suffering from P. multocida respiratory infections. Finally, data from new studies on the use of tulathromycin in exotic animals and cases of some tropical diseases are listed. The provided information gives proof for the high sensitivity of the tested pathogens to tulathromycin and high clinical and economical effect that is efficient in single dose of 2.5 mg/kg. Compared to other antibacterial agents there is no resistance according to data available so far. Local accumulation and prolonged persistence of the drug in lung tissues, that result in a treatment regime with a single low-volume dose (2.5 mg/kg), are associated with positive clinical outcome in domestic animals: large ruminants, pigs, small ruminants and rabbits with respiratory diseases caused by M. haemolytica, H. somni, P. multocida and M. bovis; A. pleuropneumoniae, B. bronchiseptica, P. multocida, H. parasuis and M. hyopneumoniae; S.aureus, C. pseudotuberculosis and Streptococcus spp. and P.multocida

Plasma Protein Binding Rate and Pharmacokinetics of Lekethromycin in Rats

Lekethromycin (LKMS), a novel macrolide lactone, is still unclear regarding its absorption. Thus, we conducted this study to investigate the characteristics of LKMS in rats. We chose the ultrafiltration method to measure the plasma protein binding rate of LKMS. As a result, LKMS was characterized by quick absorption, delayed elimination, and extensive distribution in rats following intramuscular (im) and subcutaneous (sc) administration. Moreover, LKMS has a high protein binding rate (78–91%) in rats at a concentration range of 10–800 ng/mL. LKMS bioavailability was found to be approximately 84–139% and 52–77% after im and sc administration, respectively; however, LKMS was found to have extremely poor bioavailability after oral administration (po) in rats. The pharmacokinetic parameters cannot be considered linearly correlated with the administered dose. Additionally, LKMS and its corresponding metabolites were shown to be metabolically stable in the liver microsomes of rats, dogs, pigs, and humans. Notably, only one phase I metabolite was identified during in vitro study, suggesting most of drug was not converted. Collectively, LKMS had quick absorption but poor absorption after oral administration, extensive tissue distribution, metabolic stability, and slow elimination in rats.

Pharmacokinetics of tildipirosin in horses after intravenous and intramuscular administration and its potential muscle damage

Tildipirosin is a novel semisynthetic macrolide antibiotic exclusively used in veterinary practice to treat respiratory infections. There are no pharmacokinetic or safety information available regarding the use of tildipirosin after intramuscular administration in horses. Thus, the objective of this work was to determine the disposition kinetics of tildipirosin after intravenous (IV) and intramuscular (IM) administration in horses and its potential muscle damage and cardiotoxicity. Six mature, Spanish-breed horses were used in a crossover study with a washout period of 30 days. Tildipirosin (18%) was administered at single doses by IV (2 mg/kg) and IM (4 mg/kg) routes. Tildipirosin plasma concentrations were determined by HPLC assay with ultraviolet detection. Muscle damage and inflammation were assessed by creatine kinase (CK) and haptoglobin (Hp), respectively. Creatine kinase myocardial band (CK-MB) and troponin (Tn) were used to evaluate cardiotoxicity. Tildipirosin in horses reached peak concentrations (C_max = 1.13 μg/mL) at 0.60 h (t_max) after IM administration with an absolute bioavailability of 109.2%. Steady-state volume of distribution and clearance were 3.31 ± 0.57 L/kg and 0.22 ± 0.02 L/h/kg, respectively. Tildipirosin did not cause cardiotoxicity since CK-MB and Tn basal levels were not significantly different from those obtained after several days post-administration. Mild local reactions were observed after IM administration. This local inflammation was associated with mild myolysis (CK 239-837 UI/L), which was detectable for 48 h. In brief, tildipirosin could help to treat respiratory infections in horses because it showed extensive distribution, high bioavailability and did not provoke general adverse reactions.

Pharmacokinetic/Pharmacodynamic Relationships of Tulathromycin Against Actinobacillus pleuropneumoniae in a Porcine Tissue Cage Infection Model

Tulathromycin is a semi-synthetic macrolide antibiotic that is highly effective in treating respiratory tract bacterial infections. We evaluated the in vivo antibacterial activity of tulathromycin against Actinobacillus pleuropneumoniae in piglets and determined its pharmacokinetic/pharmacodynamic (PK/PD) relationships using a tissue cage infection model. A. pleuropneumoniae (108 CFU/ml) was exposed to tulathromycin via intramuscular injection followed by a collection of cage tissue fluids at various intervals. The percentage of time the drug concentration remained above the minimum inhibitory concentration (MIC) divided by the dosing interval (%T > MIC) was the best PK/PD index to describe the antibacterial efficacy of tulathromycin (R 2 = 0.9421). The %T > MIC values required to achieve 1 - log10CFU/ml reductions and bactericidal activity (3 - log10CFU/ml reduction) were 50.8 and 96.38%, respectively. These results demonstrated that maintaining %T > MIC above 96.38% achieved bactericidal activity and thereby optimized the clinical dosage.

Pharmacokinetics of tulathromycin on plasma and semen of beef bulls

The objective of this investigation was to evaluate the pharmacokinetic parameters of tulathromycin in plasma and semen of beef bulls after administering a single sc dose at two different sites in the neck. Four Simmental bulls with excellent temperament received a comprehensive physical exam that included breeding soundness examination. In addition, blood was collected and analyzed for CBC and chemical panel in order to rule out any subclinical liver or kidney disease. All bulls were diagnosed as healthy and satisfactory potential breeders. The mean plasma levels of tulathromycin for the two neck sites of sc administration were not different between posterior aspect of the ear where it attaches to the head (RP; regio parotidea; 77.9 ± 43.3 ng/mL; X ± SD) and to the middle of the neck (RC; regio collis lateralis; 73.7 ± 39.7 ng/mL; P = 0.84). The mean seminal plasma levels of tulathromycin after administration in the RP was 608 ± 374 ng/mL and for RC was 867 ± 599 ng/mL without differences between both sites (P = 0.29). The mean level of tulathromycin in plasma was 75.8 ± 40.2 ng/mL, which was lower than mean seminal plasma levels of 781 ± 482 ng/mL (P = 0.001). The plasma peak tulathromycin concentration (C_max) was 160 ± 27 ng/mL at 21 ± 6 h (T_max) post-administration. The seminal plasma C_max was 1539 ± 44.4 ng/mL at 33.00 ± 18.00 h (T_max) post-administration. The C_max between plasma and seminal plasma were different (P = 0.008) without any differences in T_max between plasma and seminal plasma (P = 0.35). The terminal half-life for plasma tulathromycin (81.4 ± 27.6 h) showed a tendency to be shorter than in seminal plasma (114.7 ± 21.7; P = 0.10). The plasma area under the curve concentration time from the first to the last sample (AUC_0-last) was 15,440 ± 1717 ng/mL/h, which was significatively smaller compared with 171,071 ± 58,556 ng/mL/h for seminal plasma AUC_0-last (P = 0.01). The plasma means residence time from the first to the last sample (MRT_0-last) was 89.3 ± 5.1 h and it was shorter than for seminal plasma of 96.6 ± 5.0 h (P = 0.05). From the present investigation, it was concluded that tulathromycin is a suitable antibiotic based in its pharmacokinetic properties that could be used for treatment of bull genital infections when its application is indicated.

In vivo Pharmacokinetic/Pharmacodynamic (PK/PD) Profiles of Tulathromycin in an Experimental Intraperitoneal Haemophilus parasuis Infection Model in Neutropenic Guinea Pigs

Tulathromycin is a semi-synthetic macrolide antimicrobial that has an important role in veterinary medicine for respiratory disease. The objective of the study was to develop a pharmacokinetic/pharmacodynamic (PK/PD) model to examine the efficacy and determine an optimal dosage of tulathromycin intramuscular (IM) treatment against Haemophilus parasuis infection induced after intraperitoneal inoculation in neutropenic guinea pigs. The PKs of tulathromycin in serum and lung tissue after intramuscular administration at doses of 1, 10, and 20 mg/kg in H. parasuis-infected neutropenic guinea pigs were evaluated by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The tulathromycin minimum inhibitory concentration (MIC) against H. parasuis was ~16 times lower in guinea pig serum (0.03 μg/mL) than in cation-adjusted Mueller-Hinton broth (CAMHB) (0.5 μg/mL). The ratio of the 168-h area under the concentration-time curve (AUC) to MIC (AUC168h/MIC) positively correlated with the in vivo antibacterial effectiveness of tulathromycin (R 2 = 0.9878 in serum and R 2 = 0.9911 in lung tissue). The computed doses to achieve a reduction of 2-log10 CFU/lung from the ratios of AUC72h/MIC were 5.7 mg/kg for serum and 2.5 mg/kg for lung tissue, which lower than the values of 13.2 mg/kg for serum and 8.9 mg/kg for lung tissue with AUC168h/MIC. In addition, using as objective a 2-log10 reduction and an AUC0-72h as the value of the PK/PD index could be more realistic. The results of this study could provide a solid foundation for the application of PK/PD models in research on macrolide antibiotics used to treat respiratory diseases.

Pharmacokinetics of tulathromycin in pregnant ewes (Ovis aries) challenged with Campylobacter jejuni

The purpose of this study was to evaluate the pharmacokinetics of tulathromycin in the plasma and maternal and fetal tissues of pregnant ewes when administered within 24 hours of a single, IV Campylobacter jejuni (C. jejuni) challenge. Twelve, pregnant ewes between 72-92 days of gestation were challenged IV with C. jejuni IA3902 and then treated with 1.1 ml/45.36 kg of tulathromycin subcutaneously 18 hours post-challenge. Ewes were bled at predetermined time points and euthanized either at a predetermined time point or following the observation of vaginal bleeding or abortion. Following euthanasia, tissues were collected for bacterial culture, pharmacokinetics and histologic examination. The maximum (geometric) mean tulathromycin plasma concentration was estimated at 0.302 μg/mL, with a peak level observed at around 1.2 hours. The apparent systemic clearance of tulathromycin was estimated at 16.6 L/h (or 0.28 L/kg/h) with an elimination half-life estimated at approximately 22 hours. The mean tissue concentrations were highest in the uterus (2.464 μg/g) and placentome (0.484 μg/g), and were lowest in fetal liver (0.11 μg/g) and fetal lung (0.03 μg/g). Compared to previous reports, results of this study demonstrate that prior IV administration of C. jejuni appeared to substantially alter the pharmacokinetics of tulathromycin, reducing both the peak plasma concentrations and elimination half-life. However, additional controlled trials are required to confirm those observations.

Antibacterial Residue Excretion via Urine as an Indicator for Therapeutical Treatment Choice and Farm Waste Treatment

Many of the infectious diseases that affect livestock have bacteria as etiological agents. Thus, therapy is based on antimicrobials that leave the animal's tissues mainly via urine, reaching the environment through slurry and waste water. Once there, antimicrobial residues may lead to antibacterial resistance as well as toxicity for plants, animals, or humans. Hence, the objective was to describe the rate of antimicrobial excretion in urine in order to select the most appropriate molecule while reducing harmful effects. Thus, 62 pigs were treated with sulfamethoxypyridazine, oxytetracycline, and enrofloxacin. Urine was collected through the withdrawal period and analysed via LC-MS/MS. Oxytetracycline had the slowest rate of degradation (a half-life time of 4.18 days) and the most extended elimination period in urine (over 2 months), followed by enrofloxacin (a half-life time of 1.48 days, total urine elimination in ca. 3 weeks) and sulfamethoxypyridazine (a half-life time of 0.49 days, total urine elimination in ca. 1 week). Bacterial sensitivity and recommendations for responsible use are limiting when selecting the treatment. Nevertheless, with similar effectiveness, sulfamethoxypyridazine would be the choice, as waste treatment would only need to be implemented for 1 week after treatment. Thus, more in-depth knowledge regarding antibacterial elimination would improve resource management, while protecting animals and consumers' health.

Metagenomic Analysis of the Fecal Archaeome in Suckling Piglets Following Perinatal Tulathromycin Metaphylaxis

Simple Summary

The archaeal population, or ‘archaeome’, is comprised of unicellular microorganisms with a distinct biology compared with bacteria and has been shown to be an important component of host-associated microbes. While the impact of antimicrobial administration on gastrointestinal microbiota has been widely evaluated, no metagenomics-based analysis has been performed to assess the impact of an early life antimicrobials intervention on the fecal archaeome in swine. The aim of this study was therefore to investigate the impact of perinatal tulathromycin (TUL) administration on the fecal archaeome composition and diversity in suckling piglets using metagenomic sequencing analysis. Our results suggest that perinatal TUL metaphylaxis seems to have a minimal effect on the gut archaeome composition and diversity in sucking piglets.

Abstract

The gastrointestinal microbiome plays an important role in swine health and wellbeing, but the gut archaeome structure and function in swine remain largely unexplored. To date, no metagenomics-based analysis has been done to assess the impact of an early life antimicrobials intervention on the gut archaeome. The aim of this study was to investigate the effects of perinatal tulathromycin (TUL) administration on the fecal archaeome composition and diversity in suckling piglets using metagenomic sequencing analysis. Sixteen litters were administered one of two treatments (TUL; 2.5 mg/kg IM and control (CONT); saline 1cc IM) soon after birth. Deep fecal swabs were collected from all piglets on days 0 (prior to treatment), 5, and 20 post intervention. Each piglet’s fecal archaeome was composed of rich and diverse communities that showed significant changes over time during the suckling period. At the phylum level, 98.24% of the fecal archaeome across all samples belonged to Euryarchaeota. At the genus level, the predominant archaeal genera across all samples were Methanobrevibacter (43.31%), Methanosarcina (10.84%), Methanococcus (6.51%), and Methanocorpusculum (6.01%). The composition and diversity of the fecal archaeome between the TUL and CONT groups at the same time points were statistically insignificant. Our findings indicate that perinatal TUL metaphylaxis seems to have a minimal effect on the gut archaeome composition and diversity in sucking piglets. This study improves our current understanding of the fecal archaeome structure in sucking piglets and provides a rationale for future studies to decipher its role in and impact on host robustness during this critical phase of production.

Evaluation of the clinical efficacy of a water soluble formulation of tylvalosin in the control of enzootic pneumonia associated with Mycoplasma hyopneumoniae and Pasteurella multocida in pigs

Background

The efficacy of a water soluble formulation of tylvalosin (Aivlosin® 625 mg/g granules) was evaluated in the treatment and metaphylaxis of Enzootic Pneumonia (EP) in pigs. In all four trials, pigs in the tylvalosin group were administered 10 mg tylvalosin/kg bodyweight in drinking water daily for 5 consecutive days (TVN). In a single-challenge study, pigs were inoculated with lung homogenate containing Mycoplasma hyopneumoniae. In a dual challenge study, pigs were sequentially inoculated with pure culture of M. hyopneumoniae and Pasteurella multocida. Efficacy was evaluated based on reduction of lung lesions compared to unmedicated control pigs (CTL). In two field studies at European commercial farms with confirmed outbreaks of EP, treatment efficacy in clinically affected fatteners was evaluated based on improved clinical conditions compared to pigs treated with tylosin at 10 mg/kg by injection for 3 consecutive days (TYL). In these field trials, healthy in contact pigs were enrolled for metaphylaxis efficacy evaluation based on reduction in incidence of new clinical cases of respiratory disease compared to unmedicated pigs (CTL).

Results

In the M. hyopneumoniae-only challenge study, pigs in TVN group had lower lung lesion scores than CTL (6.52 vs. 14.97; p <  0.001). In the dual challenge study with M. hyopneumoniae and P. multocida, pigs in TVN group had lower lung lesion scores than CTL (3.32 vs. 8.37; p <  0.01) and the recovery of both challenge bacteria from the lungs was lower in TVN compared with CTL group (p <  0.01). In field outbreaks of EP, multicentre analysis showed that 13 days after the start of medication, treatment success for TVN pigs was significantly better than for TYL pigs (80.0% vs 48.7% p = 0.03) and metaphylactic administration of TVN significantly reduced the incidence of new clinical cases (2.1% vs. 7.8%; p <  0.01) compared with unmedicated controls.

Conclusions

Tylvalosin at 10 mg/kg daily for 5 days in drinking water was safe and effective in the treatment and metaphylaxis of EP in pigs associated with infections of M. hyopneumoniae either alone or in combination with P. multocida under both experimental challenge and field natural infection conditions.

The pharmacokinetic/pharmacodynamic paradigm for antimicrobial drugs in veterinary medicine: Recent advances and critical appraisal

Pharmacokinetic/pharmacodynamic (PK/PD) modelling is the initial step in the semi-mechanistic approach for optimizing dosage regimens for systemically acting antimicrobial drugs (AMDs). Numerical values of PK/PD indices are used to predict dose and dosing interval on a rational basis followed by confirmation in clinical trials. The value of PK/PD indices lies in their universal applicability amongst animal species. Two PK/PD indices are routinely used in veterinary medicine, the ratio of the area under the curve of the free drug plasma concentration to the minimum inhibitory concentration (MIC) (fAUC/MIC) and the time that free plasma concentration exceeds the MIC over the dosing interval (fT > MIC). The basic concepts of PK/PD modelling of AMDs were established some 20 years ago. Earlier studies have been reviewed previously and are not reconsidered in this review. This review describes and provides a critical appraisal of more recent, advanced PK/PD approaches, with particular reference to their application in veterinary medicine. Also discussed are some hypotheses and new areas for future developments.First, a brief overview of PK/PD principles is presented as the basis for then reviewing more advanced mechanistic considerations on the precise nature of selected indices. Then, several new approaches to selecting PK/PD indices and establishing their numerical values are reviewed, including (a) the modelling of time-kill curves and (b) the use of population PK investigations. PK/PD indices can be used for dose determination, and they are required to establish clinical breakpoints for antimicrobial susceptibility testing. A particular consideration is given to the precise nature of MIC, because it is pivotal in establishing PK/PD indices, explaining that it is not a "pharmacodynamic parameter" in the usual sense of this term.

Efficacy of gamithromycin injection administered intramuscularly against bacterial swine respiratory disease

The aim of this study is to evaluate the safety and efficacy of gamithromycin (GAM) for the treatment of naturally occurring bacterial swine respiratory disease (SRD) administered IM. A total of 240 pigs (nine-weeks old) were selected from two sites in Heilongjiang Province of China. The pigs showed severe signs of respiratory disease. Among them, 120 pigs were randomly divided into 4 groups of low dose (3 mg/kg), middle dose (6 mg/kg), high dose (12 mg/kg) GAM IM injection and 2.5 mg/kg tulathromycin (TUL) IM injection (positive control group) for phase II clinical trial to screen effective therapeutic dose. The other 120 pigs were randomly divided into 2 groups of 6 mg/kg GAM IM injection and 2.5 mg/kg TUL IM injection (positive control group) for phase III clinical trial to further confirm the efficacy. Animals were clinically observed daily for 14 days after treatment initiation. The predominant pathogens present in pretreatment respiratory tract samples were Streptococcus suis (S. suis) and Actinobacillus pleuropneumoniae (A. pleuropneumoniae). Haemophilus parasuis (H. parasuis) and Pasteurella multocida (P. multocida) were also found in the respiratory tract. All isolates were subjected to in vitro sensitivity testing and the measured minimal inhibitory concentrations (MIC) of GAM were from 0.0625 μg/mL to 8 μg/mL. In all treatment groups, rectal temperature dropped and clinical index (mental status and respiratory symptom) significantly improved after treatment (P ≤ .05). As a result, 82.76% animals treated with the 6 mg/kg GAM injection were cured. This was significantly higher than that of 3 mg/kg GAM injection (P ≤ .05) and similar to that of 12 mg/kg GAM injection and 2.5 mg/kg TUL injection (P > .05) in phase II clinical trial. In phase III clinical trial, 80.70% of animals treated with the 6 mg/kg GAM injection were cured and the cure rate was similar to that of 2.5 mg/kg TUL injection (P > .05). In conclusion, we recommended a single dose (6 mg/kg) of GAM IM injection for the treatment of bacterial SRD.

Negligible Impact of Perinatal Tulathromycin Metaphylaxis on the Developmental Dynamics of Fecal Microbiota and Their Accompanying Antimicrobial Resistome in Piglets

While the antimicrobial resistance profiles of cultured pathogens have been characterized in swine, the fluctuations in antimicrobial resistance genes (ARGs) associated with the developing gastrointestinal microbiota have not been elucidated. The objective of this study was to assess the impact of perinatal tulathromycin (TUL) metaphylaxis on the developmental dynamics of fecal microbiota and their accompanying antimicrobial resistome in pre-weaned piglets. Sixteen litters were given one of two treatments [control group (CONT; saline 1cc IM) and TUL group (TUL; 2.5 mg/kg IM)] directly after birth. Deep fecal swabs were collected at day 0 (prior to treatment), and again at days 5 and 20 post treatment. Shotgun metagenomic sequencing was performed on the extracted DNA, and the fecal microbiota structure and abundance of ARGs were assessed. Collectively, the swine fecal microbiota and their accompanying ARGs were diverse and established soon after birth. Across all samples, a total of 127 ARGs related to 19 different classes of antibiotics were identified. The majority of identified ARGs were observed in both experimental groups and at all-time points. The magnitude and extent of differences in microbial composition and abundance of ARGs between the TUL and CONT groups were statistically insignificant. However, both fecal microbiota composition and ARGs abundance were changed significantly between different sampling days. In combination, these results indicate that the perinatal TUL metaphylaxis has no measurable benefits or detriment impacts on fecal microbiota structure and abundance of ARGs in pre-weaned piglets.

Effect of age on the pharmacokinetics and distribution of tulathromycin in interstitial and pulmonary epithelial lining fluid in healthy calves

OBJECTIVE To compare the plasma pharmacokinetics of tulathromycin between 3-week-old (preweaned) and 6-month-old (weaned) calves and to characterize the distribution of tulathromcyin into pulmonary epithelial lining fluid (PELF) and interstitial fluid (ISF) of preweaned and weaned calves following SC administration of a single dose (2.5 mg/kg). ANIMALS 8 healthy 3-week-old and 8 healthy 6-month-old Holstein steers. PROCEDURES A jugular catheter and SC ultrafiltration probe were aseptically placed in the neck of each calf before tulathromycin administration. Blood, ISF, and bronchoalveolar lavage fluid samples were collected at predetermined times before and after tulathromycin administration for quantification of drug concentration. A urea dilution method was used to estimate tulathromycin concentration in PELF from that in bronchoalveolar lavage fluid. Tulathromycin-plasma protein binding was determined by in vitro methods. Plasma pharmacokinetics were determined by a 2-compartment model. Pharmacokinetic parameters and drug concentrations were compared between preweaned and weaned calves. RESULTS Clearance and volume of distribution per fraction of tulathromycin absorbed were significantly greater for weaned calves than preweaned calves. Tulathromycin-plasma protein binding was significantly greater for weaned calves than preweaned calves. Maximum PELF tulathromycin concentration was significantly greater than the maximum plasma and maximum ISF tulathromycin concentrations in both groups. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that age affected multiple pharmacokinetic parameters of tulathromycin, likely owing to physiologic changes as calves mature from preruminants to ruminants. Knowledge of those changes may be useful in the development of studies to evaluate potential dose adjustments during treatment of calves with respiratory tract disease.

Mutant prevention and minimum inhibitory concentration drug values for enrofloxacin, ceftiofur, florfenicol, tilmicosin and tulathromycin tested against swine pathogens Actinobacillus pleuropneumoniae, Pasteurella multocida and Streptococcus suis

Actinobacillus pleuropneumoniae, Pasteurella multocida and Streptococcus suis are prevalent bacterial causes of swine infections. Morbidity, mortality and positively impacting the financial burden of infection occurs with appropriate antimicrobial therapy. Increasing antimicrobial resistance complicates drug therapy and resistance prevention is now a necessity to optimize therapy and prolong drug life. Mutant bacterial cells are said to arise spontaneously in bacterial densities of 107-109 or greater colony forming units/ml. Antibiotic drug concentration inhibiting growth of the least susceptible cell in these high density populations has been termed the mutant prevention concentration (MPC). In this study MPC and minimum inhibitory concentration (MIC) values of ceftiofur, enrofloxacin, florfenicol, tilmicosin and tulathromycin were determined against the swine pathogens A. pleuropneumoniae, P.multocida and S. suis. The following MIC90/MPC90 values (mg/L) for 67 A. pleuropneumoniae and 73 P. multocida strains respectively were as follows: A. pleuropneumoniae 0.031/0.5, ≤0.016/0.5, 0.5/2, 4/32, 2/32; P. multocida 0.004/0.25, 0.016/0.125, 0.5/0.5, 8/16, 0.5/1. For 33 S. suis strains, MIC90 values (mg/L) respectively were as follows: 1, 0.25, 4, ≥8 and ≥8. A total of 16 S. suis strains with MIC values of 0.063-0.5 mg/L to ceftiofur and 0.25-0.5 mg/L to enrofloxacin were tested by MPC; MPC values respectively were 0.5 and 1 mg/L respectively. MPC concentrations provide a dosing target which may serve to reduce amplification of bacterial subpopulations with reduced antimicrobial susceptibility. Drug potency based on MIC90 values was ceftiofur > enrofloxacin >florfenicol = tulathromycin > tilmicosin; based on MPC90 values was enrofloxacin > ceftiofur > tulathromycin > florfenicol ≥ tilmicosin.

Pharmacokinetic/pharmacodynamic (PK/PD) evaluation of tulathromycin against Haemophilus parasuis in an experimental neutropenic guinea pig model

The objective of the study was to develop an ex-vivo PK/PD model of intramuscular (IM) administration of tulathromycin and to test its efficacy against Haemophilus parasuis (H. parasuis) infection in intraperitoneal-inoculated neutropenic guinea pigs. The pharmacokinetics (PKs) of tulathromycin at doses of 1 and 10 mg/kg in H. parasuis-infected neutropenic guinea pig were studied by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). In vitro minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), mutant prevention concentration (MPC), post-antibiotic effect (PAE) and dynamic time-kill curve experiments were carried out using H. parasuis strain 13R. Tulathromycin exhibited concentration-dependent activity and PAE persisted long after administration of the antibiotic. The ratio of the 24-h area under the concentration–time curve (AUC) to MIC in serum (AUC_24h/MIC_serum) was recognized as an important PK/PD parameter that positively correlated with the in vitro antibacterial effectiveness of tulathromycin (R² = 0.9961 or R² = 1). For the 1 and 10 mg/kg treatments with tulathromycin, the values of AUC_24h/MIC for H. parasuis bacteriostatic action, bactericidal action and virtual bacterial eradication were respectively 22.73, 34.5 and 88.03 h for the 1 mg/kg treatment and respectively 24.94, 30.94 and 49.92 h for the 10 mg/kg treatment. In addition, we demonstrated that doses of 7.2–8.0 mg/kg of tulathromycin resulted in high eradication rates (99.99%). Using a previously published conversion factor of 0.296, we were able to estimate an approximate dose, 2.1–2.4 mg/kg, that should also obtain high eradication rates in the target animal, pigs. This study can help optimize tulathromycin efficacy against H. parasuis infections in swine farming.

A novel experimental intraperitoneal infection model for Haemophilus parasuis in neutropenic guinea pigs

INTRODUCTION

Haemophilus parasuis, one of the major swine pathogens, has at least fifteen different types, all of which have significant economic effects on the global swine industry. The aim of this study was to establish an experimental intraperitoneal infection model for H. parasuis in neutropenic guinea pigs.

METHODS

Intraperitoneal administration of cyclophosphamide and Haemophilus parasuis was conducted in guinea pigs. Clinical signs, gross pathology, and histopathology were observed in neutropenic guinea pigs infected with H. parasuis.

RESULTS

Intraperitoneal administration of 100 mg/kg cyclophosphamide led to immunosuppression with white blood cells, lymphocytes, and neutrophils all <1000 mm³, while no histological tissue damage was observed. Intraperitoneal administration of 10⁹ colony-forming units (CFU) of H. parasuis led to typical respiratory symptoms, 90% morbidity, and 20% mortality in a 72 h-period. Bacteriological screening revealed that multiple organs, including the heart, liver, spleen, lungs, kidneys, and blood, were infected with H. parasuis. The threshold loads of bacteria in blood and the lungs were (7.04 ± 0.53)log₁₀ CFU/mL and (6.24 ± 0.62)log₁₀ CFU/g, respectively, at 3 d after infection. Gross pathology examination showed celiac effusion, intestinal mucosal hemorrhage, and liver, spleen, or lung swelling, necrosis, and hemorrhage. Congestion, mild interstitial pneumonia, inflammatory exudation, and endothelial cell proliferation were observed in the histological examination.

DISCUSSION

All the results suggest that we have established an experimental intraperitoneal infection model for H. parasuis in neutropenic guinea pigs. It is especially useful as a tool for pharmacokinetics, pharmacodynamics, or a pharmacokinetics/pharmacodynamics (PK/PD) model of antimicrobial agents against respiratory disease.

Pharmacokinetics and Pharmacodynamics of Tildipirosin Against Pasteurella multocida in a Murine Lung Infection Model

Tildipirosin, a 16-membered-ring macrolide antimicrobial, has recently been approved for the treatment of swine respiratory disease and bovine respiratory disease. This macrolide is extensively distributed to the site of respiratory infection followed by slow elimination. Clinical efficacy has been demonstrated in cattle and swine clinical field trials. However, the pharmacokinetic/pharmacodynamic (PK/PD) index that best correlates with the efficacy of tildipirosin remains undefined. The objective of this study was to develop a PK/PD model following subcutaneous injection of tildipirosin against Pasteurella multocida in a murine lung infection model. The PK studies of unbound (f) tildipirosin in plasma were determined following subcutaneous injection of single doses of 1, 2, 4, 6, and 8 mg/kg of body weight in neutropenic lung-infected mice. The PD studies were conducted over 24 h based on twenty intermittent dosing regimens, of which total daily dose ranged from 1 to 32 mg/kg and dosage intervals included 6, 8, 12, and 24 h. The minimum inhibitory concentration (MIC) of tildipirosin against P. multocida was determined in serum. The inhibitory effect I_max model was employed for PK/PD modeling. The area under the unbound concentration-time profile over 24 h to MIC (fAUC_{0-24 h}/MIC) was the PK/PD index that best described the antibacterial activity in the murine infection model. The fAUC_{0-24 h}/MIC targets required to achieve the bacteriostatic action, a 1-log₁₀ kill and 2-log₁₀ kill of bacterial counts were 19.93, 31.89, and 53.27 h, respectively. These results can facilitate efforts to define more rational designs of dosage regimens of tildipirosin using classical PK/PD concepts for the treatment of respiratory diseases in pigs and cattle.

The pharmacokinetic-pharmacodynamic modeling and cut-off values of tildipirosin against Haemophilus parasuis

The goal of this study was to establish the epidemiological, pharmacodynamic cut-off values, optimal dose regimens for tildipirosin against Haemophilus parasuis. The minimum inhibitory concentrations (MIC) of 164 HPS isolates were determined and SH0165 whose MIC (2 μg/ml ) were selected for PD analysis. The ex vivo MIC in plasma of SH0165 was 0.25 μg/ml which was 8 times lower than that in TSB. The bacteriostatic, bactericidal and elimination activity (AUC_24h/MIC) in serum were 26.35, 52.27 and 73.29 h based on the inhibitory sigmoid E_max modeling. The present study demonstrates that 97.9% of the wild-type (WT) isolates were covered when the epidemiological cut-off value (ECV) was set at 8 μg/ml. The parameters including AUC_24h, AUC, T1/2, C_max, CL_b and MRT in PELF were 19.56, 60.41, 2.32, 4.02, 56.6, and 2.63 times than those in plasma, respectively. Regarding the Monte Carlo simulation, the CO_PD was defined as 0.5 μg/ml in vitro, and the optimal doses to achieve bacteriostatic, bactericidal and elimination effect were 1.85, 3.67 and 5.16 mg/kg for 50% target, respectively, and 2.07, 4.17 and 5.78 mg/kg for 90% target, respectively. The results of this study offer a more optimised alternative for clinical use and demonstrated that 4.17 mg/kg of tildipirosin by intramuscular injection could have an effect on bactericidal activity against HPS. These values are of great significance for the effective treatment of HPS infections, but it also be deserved to be validated in clinical practice in the future research.

Pharmacodynamic Evaluation and PK/PD-Based Dose Prediction of Tulathromycin: A Potential New Indication for Streptococcus suis Infection

Tulathromycin is the first member of the triamilide antimicrobial drugs that has been registered in more than 30 countries. The goal of this study is to provide a potential new indication of tulathromycin for Streptococcus suis infections. We investigated the pharmacokinetic and ex vivo pharmacodynamics of tulathromycin against experimental S. suis infection in piglets. Tulathromycin demonstrated a relatively long elimination half-life (74.1 h) and a mean residence time of 97.6 h after a single intramuscular administration. The minimal inhibitory concentration (MIC) and bactericidal concentration in serum were markedly lower than those in broth culture, with Mueller–Hinton broth/serum ratios of 40.3 and 11.4, respectively. The post-antibiotic effects were at 1.27 h (1× MIC) and 2.03 h (4× MIC) and the post-antibiotic sub-MIC effect values ranged from 2.47 to 3.10 h. The ratio of the area under the concentration–time curve divided by the MIC (AUC/MIC) correlated well with the ex vivo antimicrobial effectiveness of tulathromycin (R² = 0.9711). The calculated AUC_12h/MIC ratios in serum required to produce the net bacterial stasis, 1-log₁₀ and 2-log₁₀ killing activities were 9.62, 18.9, and 32.7, respectively. Based on the results of Monte Carlo simulation, a dosage regimen of 3.56 mg/kg tulathromycin was estimated to be effective, achieving for a bacteriostatic activity against S. suis infection over 5 days period. Tulathromycin may become a potential option for the treatment of S. suis infections.

Comparative therapeutic effect of steroidal and non-steroidal anti-inflammatory drugs on pro-inflammatory cytokine production in water buffalo calves (Bubalus bubalis) naturally infected with bronchopneumonia: a randomized clinical trial

In the current study, we compared the therapeutic effects of a non-steroidal and a steroidal anti-inflammatory drug on the production of pro-inflammatory cytokines, interleukin-1β (IL-1β), interleukin-6 (IL-6), interleukin-12p40 (IL-12p40), interferon gamma (IFNγ), and tumor necrosis factor alpha (TNF-α) in the blood of water buffalo (Bubalus bubalis) calves naturally infected by bronchopneumonia. Twenty-seven buffalo calves (7 ± 2-month-old, 163 ± 12 kg) reared in smallholder farms in El-Dakahlia province in Egypt were identified to have bronchopneumonia and randomly allocated into three equal groups. Ten clinically healthy buffalo calves with negative bronchoalveolar lavage results were served as negative control. Diseased calves were treated with tulathromycin alone, a combination of tulathromycin with dexamethasone (steroidal anti-inflammatory drug) or tulathromycin with flunixin meglumine (non-steroidal anti-inflammatory drug). The results revealed significant elevations (P < 0.05) in the production of selected cytokines in all diseased calves in comparison with healthy animals. Six days post-treatment, a significant inhibition (P < 0.05) in the production of all assessed cytokines was observed in the blood of all treated calves. Interestingly, the serum concentrations of IL-1β and IL-12p40 were returned to the normal levels in pneumonic calves treated with the combination therapy of tulathromycin and flunixin meglumine. A strong significant positive correlation (P < 0.05) was detected between clinical sum scoring and IL-12p40 and TNF-α concentrations. The obtained results indicate the selectively potent anti-inflammatory effect of flunixin meglumine on the production of pro-inflammatory cytokines in pneumonic buffalo calves and highlight the efficacy of flunixin meglumine in the treatment of bronchopneumonia in buffalo calves when used in combination with tulathromycin.

The determination of minimum inhibitory concentrations of selected antimicrobials for porcine Haemophilus parasuis isolates from the Czech Republic

Haemophilus parasuisisolates obtained from pigs in the Czech Republic were tested for their susceptibility to amoxicillin, penicillin, ceftiofur, enrofloxacin, tetracycline, and tulathromycin by determination of minimum inhibitory concentrations using the broth microdilution method. TheH. parasuisisolates were mostly susceptible to majority of tested antimicrobials (amoxicillin 90%, penicillin 73.3%, enrofloxacin 83.3%, and tulathromycin 83.3%). All isolates were susceptible to ceftiofur. On the other hand, no isolate was susceptible to tetracycline, 30% of tested isolates were intermediately susceptible, and 70% were resistant. These findings indicate that tested antimicrobials with the exception of tetracycline should be the preferred option used for the treatment of infection caused byH. parasuisbut due to the potential transmission of resistance from animals to humans, the use of ceftiofur is considered as a last resort option in antimicrobial treatment of animals.

Pharmacokinetic/Pharmacodynamic Modeling of Tulathromycin against Pasteurella multocida in a Porcine Tissue Cage Model

Tulathromycin, a macrolide antibiotic, is used for the treatment of respiratory disease in cattle and swine. The aim of our study was to investigate the in vitro and ex vivo activities of tulathromycin in serum, (non-inflamed) transudate, and (inflamed) exudate against Pasteurella multocida in piglets. The pharmacokinetics properties of tulathromycin were studied for serum, transudate, and exudate using a tissue cage model. In vitro antibiotic susceptibility of P. multocida and dynamic time-kill curve experiments over eight tulathromycin concentrations were determined. The ratio of 24-h area under the concentration–time curve to minimum inhibitory concentration [AUC_{(0-24 h)}/MIC] was recognized as an important pharmacokinetic/pharmacodynamic (PK/PD) parameter of tulathromycin for antibacterial efficiency (R² = 0.9969). In serum ex vivo, for bacteriostatic, bactericidal activity, and virtual bacterial eradication AUC_{(0-24 h)}/MIC values for tulathromycin were 44.55, 73.19, and 92.44 h by using sigmoid E_max model WinNonlin software, respectively, and lower values were obtained for exudate and transudate. In conjunction with the data on MIC₉₀, the dose of tulathromycin for a bacteriostatic effect and virtual elimination of P. multocida as computed using the value of the PK/PD breakpoint obtained in serum were 6.39 and 13.25 mg/kg. However, it would be preferable to calculate a dose combined with population pharmacokinetics data to optimize the dosage regimen for bacteriological and clinical cure.

Effect of Tulathromycin on Colonization Resistance, Antimicrobial Resistance, and Virulence of Human Gut Microbiota in Chemostats

To evaluate microbiological safety of tulathromycin on human intestinal bacteria, tulathromycin (0, 0.1, 1, 10, and 100 μg/mL) was added into Chemostats. Before and after drug exposure, we monitored (1) population, SCFA products, antimicrobial resistance, and colonization resistance of gut microbiota, and (2) the antimicrobial resistance genes, transferability, virulent genes, pathogenicity of Enterococus faecalis. Results showed that low level of tulathromycin did not exhibit microbiological hazard on resistance selection and colonization resistance. However, high level of tulathromycin (10 and 100 μg/mL) may disturb colonization resistance of human gut microbiota and select antimicrobial resistant E. faecalis. Most of the selected resistant E. faecalis carried resistant gene of ermB, transferable element of Tn1545 and three virulence genes (esp, cylA, and ace). One of them (E. faecalis 143) was confirmed to have higher horizontal transfer risk and higher pathogenicity. The calculated no observable adverse effect concentration (NOAEC) and microbiological acceptable daily intake (mADI) in our study was 1 μg/mL and 14.66 μg/kg.bw/day, respectively.

Pharmacokinetics of tulathromycin in edible tissues of healthy and experimentally infected pigs with Actinobacillus pleuropneumoniae

The aim of this study was the comparison of the tissue pharmacokinetics of tulathromycin in healthy pigs and pigs experimentally infected with Actinobacillus pleuropneumoniae (App). Tulathromycin was given to 24 healthy and 24 infected pigs by intramuscular injection at a single dosage of 2.5 mg kg(-1) body weight (b.w.). Pigs were euthanised at each group and then samples of liver, kidney, muscle, injection site and skin with fat were taken at scheduled time points. Drug concentrations were determined by LC-MS/MS. In this study, higher values of the area under the concentration-time curves (AUC) were calculated in all tissue samples taken from infected than healthy pigs. In pigs with App the AUCs of liver, kidney, muscle, skin with fat and injection site were 1111, 1973, 235, 181 and 2931 mg kg(-1) h, while in pigs without inflammation they were 509, 1295, 151, 111 and 1587 mg kg(-1) h, respectively. Maximum drug tissue concentrations (Cmax) in infected animals were 2370, 6650, 2016, 666 and 83,870 µg kg(-1), while in healthy pigs they were 1483, 6677, 1733, 509 and 55,006 µg kg(-1), respectively. The eliminations half-times (T1/2) were respectively longer in all tissue samples taken from infected animals (from 157.3 to 187.3 h) than in healthy ones (from 138.6 to 161.2 h). The tulathromycin tissue concentrations were significantly higher (p < 0.05) in all tissue samples of the infected pigs compared with the healthy animals at 360 h (from 0.0014 to 0.0280) and at 792 h (from 0.0007 to 0.0242) after drug administration. The results suggest that the tissue pharmacokinetic properties and residue depletion of tulathromycin can be influenced by the disease state of animals.

Network analysis of temporal functionalities of the gut induced by perturbations in new-born piglets

BACKGROUND

Evidence is accumulating that perturbation of early life microbial colonization of the gut induces long-lasting adverse health effects in individuals. Understanding the mechanisms behind these effects will facilitate modulation of intestinal health. The objective of this study was to identify biological processes involved in these long lasting effects and the (molecular) factors that regulate them. We used an antibiotic and the same antibiotic in combination with stress on piglets as an early life perturbation. Then we used host gene expression data from the gut (jejunum) tissue and community-scale analysis of gut microbiota from the same location of the gut, at three different time-points to gauge the reaction to the perturbation. We analysed the data by a new combination of existing tools. First, we analysed the data in two dimensions, treatment and time, with quadratic regression analysis. Then we applied network-based data integration approaches to find correlations between host gene expression and the resident microbial species.

RESULTS

The use of a new combination of data analysis tools allowed us to identify significant long-lasting differences in jejunal gene expression patterns resulting from the early life perturbations. In addition, we were able to identify potential key gene regulators (hubs) for these long-lasting effects. Furthermore, data integration also showed that there are a handful of bacterial groups that were associated with temporal changes in gene expression.

CONCLUSION

The applied systems-biology approach allowed us to take the first steps in unravelling biological processes involved in long lasting effects in the gut due to early life perturbations. The observed data are consistent with the hypothesis that these long lasting effects are due to differences in the programming of the gut immune system as induced by the temporary early life changes in the composition and/or diversity of microbiota in the gut.

Antimalarial activity of tulathromycin in a murine model of malaria

There is an urgent need for new antimalarial agents and strategies to treat and control malaria. This study shows an antiplasmodium effect of tulathromycin in mice infected with Plasmodium yoelii. The administration of tulathromycin around the time of infection prevented the progression of disease in 100% of the animals. In addition, highly parasitized mice treated with tulathromycin showed a decreased parasite burden and cleared the parasite faster than did untreated infected mice.

Pharmacokinetics of tulathromycin after subcutaneous injection in North American bison (Bison bison)

Tulathromycin is approved for the treatment of respiratory disease in cattle and swine. It is intended for long-acting, single-dose injection therapy (Draxxin), making it particularly desirable for use in bison due to the difficulty in handling and ease of creating stress in these animals. The pharmacokinetic properties of tulathromycin in bison were investigated. Ten wood bison received a single 2.5 mg/kg subcutaneous injection of Draxxin. Serum concentrations were measured by liquid chromatography-mass spectrometry (LC-MS) detection. Tulathromycin demonstrated early maximal serum concentrations, extensive distribution, and slow elimination characteristics. The mean maximum serum concentration (Cmax) was 195 ng/mL at 1.04 h (tmax) postinjection. The mean area under the serum concentration-time curve, extrapolated to infinity (AUC0-inf ), was 9341 ng · h/mL. The mean apparent volume of distribution (Vd /F) and clearance (Cls/F) was 111 L/kg and 0.4 L/h/kg, respectively, and the mean half-life (t1/2) was 214 h (8.9 days). Compared to values for cattle, Cmax and AUC0-inf were lower in bison, while the Vd /F was larger and the t1/2 longer. Tissue distribution and clinical efficacy studies in bison are needed to confirm the purported extensive distribution of tulathromycin into lung tissue and to determine whether a 2.5 mg/kg subcutaneous dosage is adequate for bison.

Pharmacokinetics of gamithromycin after intravenous and subcutaneous administration in pigs

The aim of this study was to investigate the pharmacokinetic properties of gamithromycin in pigs after an intravenous (i.v.) or subcutaneous (s.c.) bolus injection of 6 mg/kg body weight. The plasma concentrations of gamithromycin were determined using a validated high-performance liquid chromatography-tandem mass spectrometry method, and the pharmacokinetics were noncompartmentally analysed. Following i.v. administration, the mean area under the plasma concentration-time curve extrapolated to infinity (AUCinf) and the mean elimination half-life (t1/2λz) were 3.67 ± 0.75 μg.h/mL and 16.03 h, respectively. The volume of distribution at steady state (Vss) and the plasma clearance were 31.03 ± 6.68 L/kg and 1.69 ± 0.33 L/h.kg, respectively. The mean residence time (MRTinf) was 18.84 ± 4.94 h. Gamithromycin administered subcutaneously to pigs demonstrated a rapid and complete absorption, with a mean maximal plasma concentration (Cmax) of 0.41 ± 0.090 μg/ml at 0.63 ± 0.21 h and a high absolute bioavailability of 118%. None of the reported pharmacokinetic variables significantly differed between both administration routes.

Estimating tulathromycin withdrawal time in pigs using a physiologically based pharmacokinetics model

A physiologically based pharmacokinetics model was developed to predict tulathromycin concentrations in edible swine tissues. Physiological parameters included volumes of and plasma flows through different tissues which were obtained from the literatures. The tissue/plasma partition coefficient was calculated according to the area method, and the model was validated through a comparison of predicted and observed concentrations. Withdrawal times in different tissues were predicted. The physiologically based pharmacokinetics model presented here provided accurate predictions of the observed concentrations in all tissues. The results showed that the injection site had the longest withdrawal time (21 days), followed by skin together with fat (19 days) and then kidney (10 days), lung (6 days), liver (4 days) and muscle (1 day). A withdrawal time of 21 days was finally predicted for tulathromycin in swine after a single intramuscular injection at 2.5 mg/kg body weight.

Effects of tylosin, tilmicosin and tulathromycin on inflammatory mediators in bronchoalveolar lavage fluid of lipopolysaccharide-induced lung injury

The aim of this study was to determine the anti-inflammatory effects of macrolides through kinetic parameters in bronchoalveolar lavage fluid (BALF) of lipopolysaccharide-induced lung injury. Rats were divided into four groups: lipopolysaccharide (LPS), LPS + tylosin, LPS + tilmicosin and LPS + tulathromycin. BALF samples were collected at sampling times. TNF, IL-1β, IL-6, IL-10 and 13,14-dihydro-15-keto-prostaglandin F2α (PGM) and C-reactive protein (CRP) were analysed. Area under the curve (AUC) and maximum plasma concentration (Cmax) values of inflammatory mediators were determined by a pharmacokinetic computer programme. When inflammatory mediator concentrations were compared between the LPS group and other groups for each sampling time, the three macrolides had no pronounced depressor effect on cytokine levels, but they depressed PGM and CRP levels. In addition, tylosin and tilmicosin decreased the AUC0-24 level of TNF, while tilmicosin decreased the AUC0-24 level of IL-10. Tylosin and tulathromycin decreased the AUC0-24 of PGM, and all three macrolides decreased the AUC0-24 of CRP. Especially tylosin and tulathromycin may have more expressed anti-inflammatory effects than tilmicosin, via depressing the production of inflammatory mediators in the lung. The AUC may be used for determining the effects of drugs on inflammation. In this study, the antiinflammatory effects of these antibiotics were evaluated with kinetic parameters as a new and different approach.

Pulmonary pharmacokinetics of tulathromycin in swine. Part I: Lung homogenate in healthy pigs and pigs challenged intratracheally with lipopolysaccharide of Escherichia coli

The objective of the study was to assess the pharmacokinetics of tulathromycin in lung tissue homogenate (LT) and plasma from healthy and lipopolysaccharide (LPS)-challenged pigs. Clinically healthy pigs were allocated to two dosing groups of 36 animals each (group 1 and 2). All animals were treated with tulathromycin (2.5 mg/kg). Animals in group 2 were also challenged intratracheally with LPS from Escherichia coli (LPS-Ec) 3 h prior to tulathromycin administration. Blood and LT samples were collected from all animals during 17-day post-tulathromycin administration. For LT, one sample from the middle (ML) and caudal lobes (CL) was taken. The concentration of tulathromycin was significantly lower in the ML after the intratracheal administration of LPS-E. coli (P < 0.02). In healthy pigs and LPS-challenged animals, the distribution of the drug into the lungs was rapid and persisted at high levels for 17-day postadministration. The distribution of the drug within the lung seems to be homogenous, at least between the middle and caudal lobes within dosing groups. The concentration versus time profile of the drug and pharmacokinetic parameters in two different lung areas (middle and caudal lobe) were consistent within the groups. The clinical significance of these findings is unknown.

Pharmacokinetics of tulathromycin in healthy and neutropenic mice challenged intranasally with lipopolysaccharide from Escherichia coli

Tulathromycin represents the first member of a novel subclass of macrolides, known as triamilides, approved to treat bovine and swine respiratory disease. The objectives of the present study were to assess the concentration-versus-time profile of tulathromycin in the plasma and lung tissue of healthy and neutropenic mice challenged intranasally with lipopolysaccharide (LPS) from Escherichia coli O111:B4. BALB/c mice were randomly allocated into four groups of 40 mice each: groups T-28 (tulathromycin at 28 mg/kg of body weight), T-7, T7-LPS, and T7-LPS-CP (cyclophosphamide). Mice in group T-28 were treated with tulathromycin at 28 mg/kg subcutaneously (s.c.) (time 0 h). The rest of the mice were treated with tulathromycin at 7 mg/kg s.c. (time 0 h). Animals in dose groups T-7-LPS and T7-LPS-CP received a single dose of E. coli LPS intranasally at -7 h. Mice in group T7-LPS-CP were also rendered neutropenic with cyclophosphamide (150 mg/kg intraperitoneally) prior to the administration of tulathromycin. Blood and lung tissue samples were obtained from 5 mice from each dose group at each sampling time over 144 h after the administration of tulathromycin. There were not statistical differences in lung tissue concentrations among groups T-7, T-7-LPS, and T7-LPS-CP. For all dose groups, the distribution of tulathromycin in the lungs was rapid and persisted at relatively high levels during 6 days postadministration. The concentration-versus-time profile of tulathromycin in lung tissue was not influenced by the intranasal administration of E. coli LPS. The results suggest that in mice, neutrophils may not have a positive influence on tulathromycin accumulation in lung tissue when the drug is administered during either a neutrophilic or a neutropenic state.

Pharmacokinetics of tildipirosin in porcine plasma, lung tissue, and bronchial fluid and effects of test conditions on in vitro activity against reference strains and field isolates of Actinobacillus pleuropneumoniae

The pharmacokinetics of tildipirosin (Zuprevo(®) 40 mg/mL solution for injection for pigs), a novel 16-membered-ring macrolide for the treatment for swine respiratory disease (SRD), was investigated in studies collecting blood plasma and postmortem samples of lung tissue and bronchial fluid (BF) from swine. In view of factors influencing the in vitro activity of macrolides, and for the interpretation of tildipirosin pharmacokinetics in relation to minimum inhibitory concentrations (MIC), additional experiments were conducted to study the effects of pH, carbon dioxide-enriched atmosphere, buffers, and serum on tildipirosin MICs for various reference strains and Actinobacillus (A.) pleuropneumoniae field isolates. After single intramuscular (i.m.) injection at 4 mg/kg body weight, maximum plasma concentration (Cmax) was 0.9 μg/mL observed within 23 min (Tmax ). Mean residence time from the time of dosing to the time of last measurable concentration (MRTlast) and terminal half-life (T1/2) both were about 4 days. A dose-response relationship with no significant sex effect is observed for area under the plasma concentration-time curve from time 0 to the last sampling time with a quantifiable drug concentration (AUClast) over the range of doses up to 6 mg/kg. However, linear dose proportionality could not be proven with statistical methods. The time-concentration profile of tildipirosin in BF and lung far exceeded that in blood plasma. In lung, tildipirosin concentrations reached 3.1 μg/g at 2 h, peaked at 4.3 μg/g at day 1, and slowly declined to 0.8 μg/g at day 17. In BF, tildipirosin levels were 14.3, 7.0, and 6.5 μg/g at days 5, 10, and 14. T1/2 in lung was ∼7 days. Tildipirosin is rapidly and extensively distributed to the respiratory tract followed by slow elimination. Culture media pH and carbon dioxide-enriched atmosphere (CO2 -EA) had a marked impact on in vitro activity of tildipirosin in reference strains of various rapidly growing aerobic and fastidious bacteria including Histophilus (H.) somni ATCC 700025 and A. pleuropneumoniae ATCC 27090. For A. pleuropneumoniae ATCC 27090 testing conditions without CO2 -EA resulted in reduced acidification of culture media pH and a reduction in the minimum inhibitory concentrations compared to standard in vitro test conditions by 2 log2 dilution steps (4-fold) from 8 to 2 μg/mL. Supplementary buffering of standard culture media resulted in a reduction in the A. pleuropneumoniae (n = 8) MIC range by 4 log2 dilution steps (16-fold) from 8-16 to 0.5-1 μg/mL. Incremental supplementation of culture media with 50% serum resulted in noticeable shifts to lower minimum or maximum MICs by at least 2 log2 dilution steps (≥4-fold) in all aerobic and fastidious reference strains tested except for Pasteurella (P.) multocida. The MIC of A. pleuropneumoniae ATCC 27090 decreased by 2-4 log2 dilution steps (4 to 16-fold) from 8 to 0.5-2 μg/mL when 50% serum was added to the standard assay. Considering a higher presence of serum and the rather neutral pH conditions maintained in vivo, it is suggested to take the influence of these factors on in vitro activity into account when interpreting tildipirosin MICs for A. pleuropneumoniae in relation to pharmacokinetics.

Antimicrobial susceptibility patterns and sensitivity to tulathromycin in goat respiratory bacterial isolates

Bacterial pneumonia is a common and often life-threatening respiratory problem in both meat and dairy goats. Options for approved antibiotic therapy in goats to combat these bacterial infections are severely limited and frequently drugs must be used in an extra-label manner. Tulathromycin, a triamilide macrolide antimicrobial drug shown to be effective against swine and cattle respiratory bacterial agents, has been identified as a potentially useful drug in caprines. The present study was conducted to determine the susceptibility of recognized bacterial respiratory pathogens to commonly prescribed antimicrobials, with a particular emphasis on the efficacy of tulathromycin against these agents. Minimum inhibitory concentration (MIC) testing using microbroth dilution was performed on a collection of 45 Mannheimia haemolytica, 11 Pasteurella multocida, and 11 Bibersteinia trehalosi isolates from the lungs of goats with clinical pneumonia. To further characterize efficacy of tulathromycin against these pathogens, minimum bactericidal concentration (MBC) testing and kinetic killing assays were conducted. Most isolates were susceptible to the antimicrobials tested; however, increased resistance as demonstrated by higher MIC values was seen in all species to penicillin, in P. multocida to sulfadimethoxine, and in B. trehalosi to the tetracyclines. All isolates were susceptible to tulathromycin, which demonstrated a high killing efficiency in both bactericidal assays. Results of this study indicate that most goat pneumonic bacterial pathogens remain susceptible to commonly prescribed antibiotics, although some evidence of resistance was seen to certain drugs; and that tulathromycin is highly effective against goat respiratory pathogens which could make it a valuable medication in this species.