In vitro pharmacodynamics of gamithromycin against Mycoplasma mycoides subspecies mycoides Small Colony

Network meta-analysis of the therapeutic effects of various antibiotics on footrot in sheep and cattle

The present network meta-analysis was performed to compare the effects of antibiotics used in treating footrot in some ruminants and to rank these antibiotics based on their efficacy. Data of 14 eligible studies consisting of 5622 affected animals was included in the analysis. A Bayesian method and Markov Chain Monte Carlo (MCMC) simulations were utilized to analyze data. The estimated results were reported in the form of odds ratios (ORs) with 95% credible intervals (CrI). The Surface Under the Cumulative Ranking Curve (SUCRA) was used to rank antibiotics. Network meta-regressions (NMRs) were conducted to examine the influence of sample sizes, treatment duration, route of administration, and species of animals (sheep and cattle) on the overall outcome. The results indicated that gamithromycin impact on curing footrot was superior to other antibiotics and Lincomycin and oxytetracycline were ranked second and third. The difference between the impact of gamithromycin and amoxicillin (OR = 14.76, CrI: 1.07-193.49) and enrofloxacin (OR = 20.21, CrI: 1.57-229.25) on footrot was significant. There was a significant difference between the effect of oxytetracycline and enrofloxacin (OR = 5.24, CrI: 1.14-23.74) on footrot. The NMR performed based on species of animals fitted data better than network meta-analysis, suggesting erythromycin as the best third antibiotic instead of oxytetracycline. Egger's regression test and the shape of the funnel plot showed no publication bias among included studies. In conclusion, gamithromycin was associated with the highest curing rate benefit when used to treat footrot, followed by lincomycin and oxytetracycline/erythromycin. Among all evaluated antibiotics, enrofloxacin showed the lowest effects on footrot.

Pharmacodynamic Target Assessment and PK/PD Cutoff Determination for Gamithromycin Against Streptococcus suis in Piglets

Gamithromycin is a long-acting azalide antibiotic that has been developed recently for the treatment of swine respiratory diseases. In this study, the pharmacokinetic/pharmacodynamic (PK/PD) targets, PK/PD cutoff, and optimum dosing regimen of gamithromycin were evaluated in piglets against Streptococcus suis in China, including a subset with capsular serotype 2. Short post-antibiotic effects (PAEs) (0.5–2.6 h) and PA-SMEs (2.4–7.7 h) were observed for gamithromycin against S. suis. The serum matrix dramatically facilitated the intracellular uptake of gamithromycin by S. suis strains, thus contributing to the potentiation effect of serum on their susceptibilities, with a Mueller-Hinton broth (MHB)/serum minimum inhibitory concentration (MIC) ratio of 28.86 for S. suis. Dose-response relationship demonstrated the area under the concentration (AUC)/MIC ratio to be the predictive PK/PD index closely linked to activity (R² > 0.93). For S. suis infections, the net stasis, 1–log₁₀, and 2–log₁₀ kill effects were achieved at serum AUC_24h/MIC targets of 17.9, 49.1, and 166 h, respectively. At the current clinical dose of 6.0 mg/kg, gamithromycin PK/PD cutoff value was determined to be 8 mg/L. A PK/PD-based dose assessment demonstrated that the optimum dose regimen of gamithromycin to achieve effective treatments for the observed wild-type MIC distribution of S. suis in China with a probability of target attainment (PTA) ≥ 90% was 2.53 mg/kg in this study. These results will aid in the development of clinical dose-optimization studies and the establishment of clinical breakpoints for gamithromycin in the treatment of swine respiratory infections due to S. suis.

Epidemiological and PK/PD cutoff values determination and PK/PD-based dose assessment of gamithromycin against Haemophilus parasuis in piglets

Background

Gamithromycin is a macrolide approved for the treatment of bovine and swine respiratory diseases. Our study aims to establish the clinical breakpoint and optimum dose regimen for gamithromycin against Haemophilus parasuis in piglets.

Results

Gamithromycin was well absorbed and fully bioavailable (87.2–101%) after intramuscular and subcutaneous administrations. The MICs of gamithromycin for 192 clinical H. parasuis isolates ranged from 0.008 to 128 mg/L and the epidemiological cutoff (ECOFF) was calculated as 1.0 mg/L. A large potentiation effect of serum on in vitro susceptibility of gamithromycin was observed for H. parasuis, with broth/serum ratios of 8.93 for MICs and 4.46 for MBCs, respectively. The postantibiotic effects were 1.5 h (1 × MIC) and 2.4 h (4 × MIC), and the postantibiotic sub-MIC effects ranged from 2.7 to 4.3 h. Gamithromycin had rapid and concentration-dependent killing against H. parasuis, and the AUC_24h/MIC ratio correlated well with ex vivo efficacy (R² = 0.97). The AUC_24h/MIC targets in serum associated with bacteriostatic, bactericidal and eradication activities were 15.8, 30.3 and 41.2, respectively. The PK/PD-based population dose prediction indicated a probability of target attainment (PTA) for the current marketed dose (6 mg/kg) of 88.9% against H. parasuis. The calculated gamithromycin dose for a PTA ≥ 90% was 6.55 mg/kg. Based on Monte Carlo simulations, the PK/PD cutoff (CO_PD) was determined to be 0.25 mg/L.

Conclusion

The determined cutoffs and PK/PD-based dose prediction will be of great importance in gamithromycin resistance surveillance and serve as an important step in the establishment of optimum dose regimen and clinical breakpoints.

Pharmacokinetics and Pharmacodynamics of Gamithromycin Treatment of Pasteurella multocida in a Murine Lung Infection Model

Gamithromycin is approved for the treatment and prevention of bovine respiratory disease (BRD), which is caused mainly by Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, and Mycoplasma species. In this study, multiple dosage regimens were administered to the neutropenic mouse lung infection model in order to investigate the pharmacokinetic/pharmacodynamic (PK/PD) parameters of gamithromycin treatment of P. multocida and to further define the PK/PD parameter that best correlates with the efficacy of gamithromycin against P. multocida. The PK characteristics of gamithromycin were analyzed after a single subcutaneous (s.c.) injection (1, 3, 6, and 9 mg/kg). The concentration–time profiles of unbound (f) gamithromycin in plasma samples were analyzed by non-compartmental analysis. The main PK parameters of gamithromycin for the area under the concentration–time curve from 0 to 24 h (f AUC_0–24) and the peak drug concentration (f C_max) values ranged from 0.86 to 8.42 µg·h/ml and from 0.55 to 5.69 µg/ml, respectively. The PD values were calculated based on multiple s.c. injections over 24 h (1, 3, 6, and 9 mg/kg at 6, 8, 12, and 24 h, respectively; total dosage 1–36 mg/ kg). The minimum inhibitory concentration (MIC) of gamithromycin against P. multocida in mice serum was 0.15 μg/ml. Analysis of PK/PD indices using the inhibitory effect E_max model indicated a strong correlation (R² = 0.9624) between the f AUC_0–24/MIC ratio and various antibacterial effects. The area under the unbound concentration–time curve over 24 h to MIC (f AUC_0–24/MIC) predicted for bacteriostatic action, 1-log₁₀ reduction, 2-log₁₀ reduction, and 3-log₁₀ reduction were 56.77, 90.18, 143.06, and 239.44 h, respectively. These in vivo data may facilitate gamithromycin dosage optimization against P. multocida in veterinary medicine.

Development of molecular methods for the rapid detection of antibiotic susceptibility of Mycoplasma bovis

Determining the antibiotic susceptibility profile of Mycoplasma bovis isolates in vitro provides the basis for the appropriate choice of antibiotics in the therapy. Traditionally, the antibiotic susceptibility examination of mycoplasmas is technically demanding, time-consuming and rarely performed in diagnostic laboratories. The aim of the present study was to develop rapid molecular assays to determine mutations responsible for elevated minimal inhibitory concentrations (MICs) to fluoroquinolones, tetracyclines, aminocyclitols, macrolides, lincosamides, phenicols and pleuromutilins in M. bovis. The nine mismatch amplification mutation assays (MAMA) and seven high resolution melt (HRM) tests designed in the present study enable the simultaneous detection of these genetic markers. The sensitivity of the assays varied between 10²-10⁵ copy numbers/reaction. Cross-reactions with other mycoplasmas occurring in cattle were detected in assays targeting universal regions (e.g. 16S rRNA). Nevertheless, results of the novel method were in accordance with sequence and MICs data of the M. bovis pure cultures. Also, the tests of clinical samples containing high amount of M. bovis DNA were congruent even in the presence of other Mycoplasma spp. The presented method is highly cost-effective and can provide an antibiogram to 12 antibiotics in approximately 3-4 days when previous isolation of M. bovis is applied. In order to assure the proper identification of the genetic markers at issue, the regions examined by the MAMA and HRM tests are overlapping. In conclusion, the developed assays have potential to be used in routine diagnostics for the detection of antibiotic susceptibility in M. bovis.

Impact of growth matrix on pharmacodynamics of antimicrobial drugs for pig pneumonia pathogens

Background

The most widely used measure of potency of antimicrobial drugs is Minimum Inhibitory Concentration (MIC). MIC is usually determined under standardised conditions in broths formulated to optimise bacterial growth on a species-by-species basis. This ensures comparability of data between laboratories. However, differences in values of MIC may arise between broths of differing chemical composition and for some drug classes major differences occur between broths and biological fluids such as serum and inflammatory exudate. Such differences must be taken into account, when breakpoint PK/PD indices are derived and used to predict dosages for clinical use. There is therefore interest in comparing MIC values in several broths and, in particular, in comparing broth values with those generated in serum. For the pig pneumonia pathogens, Actinobacillus pleuropneumoniae and Pasteurella multocida, MICs were determined for three drugs, florfenicol, oxytetracycline and marbofloxacin, in five broths [Mueller Hinton Broth (MHB), cation-adjusted Mueller Hinton Broth (CAMHB), Columbia Broth supplemented with NAD (CB), Brain Heart Infusion Broth (BHI) and Tryptic Soy Broth (TSB)] and in pig serum.

Results

For each drug, similar MIC values were obtained in all broths, with one exception, marbofloxacin having similar MICs for three broths and 4–5-fold higher MICs for two broths. In contrast, for both organisms, quantitative differences between broth and pig serum MICs were obtained after correction of MICs for drug binding to serum protein (fu serum MIC). Potency was greater (fu serum MIC lower) in serum than in broths for marbofloxacin and florfenicol for both organisms. For oxytetracycline fu serum:broth MIC ratios were 6.30:1 (P. multocida) and 0.35:1 (A. pleuropneumoniae), so that potency of this drug was reduced for the former species and increased for the latter species. The chemical composition of pig serum and broths was compared; major matrix differences in 14 constituents did not account for MIC differences. Bacterial growth rates were compared in broths and pig serum in the absence of drugs; it was concluded that broth/serum MIC differences might be due to differing growth rates in some but not all instances.

Conclusions

For all organisms and all drugs investigated in this study, it is suggested that broth MICs should be adjusted by an appropriate scaling factor when used to determine pharmacokinetic/pharmacodynamic breakpoints for dosage prediction.

Observations on macrolide resistance and susceptibility testing performance in field isolates collected from clinical bovine respiratory disease cases

The objectives of this study were; first, to describe gamithromycin susceptibility of Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni isolated from cattle diagnosed with bovine respiratory disease (BRD) and previously treated with either gamithromycin for control of BRD (mass medication=MM) or sham-saline injected (control=CON); second, to describe the macrolide resistance genes present in genetically typed M. haemolytica isolates; third, use whole-genome sequencing (WGS) to correlate the phenotypic resistance and genetic determinants for resistance among M. haemolytica isolates. M. haemolytica (n=276), P. multocida (n=253), and H. somni (n=78) were isolated from feedlot cattle diagnosed with BRD. Gamithromycin susceptibility was determined by broth microdilution. Whole-genome sequencing was utilized to determine the presence/absence of macrolide resistance genes and to genetically type M. haemolytica. Generalized linear mixed models were built for analysis. There was not a significant difference between MM and CON groups in regards to the likelihood of culturing a resistant isolate of M. haemolytica or P. multocida. The likelihood of culturing a resistant isolate of M. haemolytica differed significantly by state of origin in this study. A single M. haemolytica genetic subtype was associated with an over whelming majority of the observed resistance. H. somni isolation counts were low and statistical models would not converge. Phenotypic resistance was predicted with high sensitivity and specificity by WGS. Additional studies to elucidate the relationships between phenotypic expression of resistance/genetic determinants for resistance and clinical response to antimicrobials are necessary to inform judicious use of antimicrobials in the context of relieving animal disease and suffering.

The PK/PD Interactions of Doxycycline against Mycoplasma gallisepticum

Mycoplasma gallisepticum is one of the most important pathogens that cause chronic respiratory disease in chicken. This study investigated the antibacterial activity of doxycycline against M. gallisepticum strain S6. In static time–killing studies with constant antibiotic concentrations [0–64 minimum inhibitory concentration (MIC)], M. gallisepticum colonies were quantified and kill rates were calculated to estimate the drug effect. The half-life of doxycycline in chicken was 6.51 ± 0.63 h. An in vitro dynamic model (the drug concentrations are fluctuant) was also established and two half-lives of 6.51 and 12 h were simulated. The samples were collected for drug concentration determination and viable counting of M. gallisepticum. In static time–killing studies, doxycycline produced a maximum antimycoplasmal effect of 5.62log₁₀ (CFU/mL) reduction and the maximum kill rate was 0.11 h⁻¹. In the in vitro dynamic model, doxycycline had a mycoplasmacidal activity in the two regimens, and the maximum antimycoplasmal effects were 4.1 and 4.75log₁₀ (CFU/mL) reduction, respectively. Furthermore, the cumulative percentage of time over a 48-h period that the drug concentration exceeds the MIC (%T > MIC) was the pharmacokinetic–pharmacodynamic index that best correlated with antimicrobial efficacy (R² = 0.986, compared with 0.897 for the peak level divided by the MIC and 0.953 for the area under the concentration–time curve over 48 h divided by the MIC). The estimated %T > MIC values for 0log₁₀ (CFU/mL) reduction, 2log10 (CFU/mL) reduction and 3log₁₀ (CFU/mL) reduction were 32.48, 45.68, and 54.36%, respectively, during 48 h treatment period of doxycycline. In conclusion, doxycycline shows excellent effectiveness and time-dependent characteristics against M. gallisepticum strain S6 in vitro. Additionally, these results will guide optimal dosing strategies of doxycycline in M. gallisepticum infection.

Ex vivo pharmacokinetic and pharmacodynamic analysis of valnemulin against Mycoplasma gallisepticum S6 in Mycoplasma gallisepticum and Escherichia coli co-infected chickens

Pharmacokinetic and pharmacodynamic (PK/PD) indices against Mycoplasma gallisepticum (MG) S6 were investigated in an ex vivo PK/PD model following oral administration of valnemulin to chickens co-infected with M. gallisepticum and Escherichia coli. The minimum inhibitory concentrations (MICs) for valnemulin against MG S6 in artificial medium and chicken serum were determined. In vitro time-killing curves were established according to a series of multiples of the MIC value in an artificial medium, and ex vivo time-killing curves were established in serum samples obtained from infected chickens at different time points after oral administration with an initial titer of 1 × 10(6) color change units (CCU)/mL MG S6. The sigmoid Emax model was used to provide 24 h area under concentration-time curve/minimum inhibitory concentration ratios (AUC0-24h/MIC) for mycoplasmastasis, mycoplasmacidal activity and mycoplasmal elimination, respectively. The inoculum size and micro or macro methods exhibited little effect on MIC determination of MG, whereas matrix had a large effect. The rapid killing activity observed in in vitro time-killing curves seems to indicate that valnemulin was mycoplasmacidal and concentration dependent against MG. The AUC0-24h/MIC ratio for mycoplasmacidal activity and mycoplasmal elimination was 1321 h and 1960 h, respectively. A dosage regimen of 12.4 mg/kg/day and 18.3 mg/kg/day valnemulin was calculated for mycoplasmacidal activity and mycoplasmal elimination against MG S6, respectively.