Integration and modelling of pharmacokinetic and pharmacodynamic data to optimize dosage regimens in veterinary medicine

Pharmacokinetics of bromoform in dairy heifers

AIMS

To determine the pharmacokinetics in dairy heifers after oral and IV administration of bromoform, a potential antimethanogenic agent found in red seaweed, Asparagopsis spp.

METHODS

Twenty-four dairy heifers with a mean weight of 319 (SD 36.9) kg were used. The study was conducted in two phases, and each cohort of 12 heifers received an escalating dose of bromoform. In the first phase, 12 heifers successively received doses of 200, 400, 800, and 1600 mg of bromoform orally, separated by a 72-hour washout period. In the second phase, a different cohort of 12 dairy heifers was used. Each heifer received a total of four doses of bromoform separated by a wash-out period of 72 hours. Sequentially the treatments were (for each of the 12 heifers) an oral dose of 50 mg, followed by an IV dose of 50 mg, followed by an oral dose of 100 mg and finally an IV dose of 100 mg.Blood samples were assayed by gas chromatography-mass spectrophotometry for bromoform and dibromomethane to estimate the pharmacokinetic parameters using a non-compartmental analysis.

RESULTS

Bromoform was rapidly absorbed as indicated by a short time to the maximum observed concentration of 15 minutes. For the routes of administration and dose ranges investigated, the mean terminal half-life ranged from 0.32 (SE 0.03) hours to 5.73 (SE 1.64) hours when administered orally or IV. With values for the mean area under the curve (AUC) to dose ratio ranging from 0.25 (SE 0.04) to 0.82 (SE 0.19) for oral and 1.39 (SE 0.39) to 4.02 (SE 0.37) for IV administration, bromoform appeared to exhibit non-proportional pharmacokinetic behaviour. The mean absolute bioavailability was 39.13 (SE 10.4)% and 3.36 (SE 0.83)% for 50-mg and 100-mg doses, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Bromoform is rapidly absorbed and exhibits dose dependent elimination kinetics.

Pharmacokinetic profile of oral and subcutaneous administration of paracetamol in the koala (Phascolarctos cinereus) and prediction of its analgesic efficacy

The pharmacokinetic profile of paracetamol in koalas is described when administered orally at 15 mg/kg; followed by the same dose, administered every 12 hours (hrs), repeated five times. After the initial oral administration, the median (range) maximal plasma concentration (Cmax), the time Cmax was reached (Tmax) and elimination half-life (t1/2) were 16.93 μg/mL (13.66 to 20.25 μg/mL); 4 hrs (4 to 8 hrs) and 5.54 hrs (4.66 to 7.67 hrs), respectively. When paracetamol was administered orally at 15 mg/mL every 12 hrs, the trough total plasma concentration range remained comparable to the therapeutic range in humans i.e. 4 to 20 μg/mL that is known to provide some analgesia. However, there is a smaller proportion of free drug (i.e. not bound to plasma proteins; and the active form) available in koala plasma (approximately 40% unbound) compared to human plasma (approximately 80% unbound). Consequently, even when there are similar total drug plasma concentrations in both koala and human plasma, the therapeutic efficacy may be reduced in koalas compared to humans. The initial oral dose and subsequent twice daily doses resulted in no obvious adverse effects in any koala. Haematology, plasma electrolyte and biochemical analyte values remained within their reference ranges eight hrs after the last dose but there was a significant change in alanine transaminase (ALT) levels (an increase), and in total protein (a decrease) (both p = 0.03). A dose of 15 mg/kg was also administered as a subcutaneous injection, diluted 50:50 with saline, to two koalas. As the oral formulation and the subcutaneous administration resulted in comparable absorption, the study focused on the oral profile. Based on these results there is an argument to recommend a slight increase in the oral paracetamol dose for the koala, however further investigation is required to confirm whether repeated administration of a slightly higher dose may be associated with more severe or additional significant changes in haematology, electrolytes or biochemical analytes. However, a preferable recommendation would be to administer this dosage of paracetamol in combination with another analgesic such as tramadol, as a subcutaneous injection, to improve efficacy.

Lung microdialysis and in vivo PK/PD integration of cefquinome against Actinobacillus pleuropneumoniae in a porcine experimental lung infection model

This study aim to explore the application of microdialysis in pharmacokinetic (PK) and pharmacodynamic (PD) integration of cefquinome against Actinobacillus pleuropneumoniae in a porcine experimental lung infection model. The model was established via intratracheal inoculation where average bacterial counts (CFU) in the lungs of infected pigs reached 6.57 log10 CFU/g after 3 h. The PK profiles of unbound cefquinome in lung dialysates were determined following intramuscular injection of single doses of 0.125, 0.25, 0.5, 1, 2, and 4 mg/kg. Lung dialysate samples were collected using microdialysis at a flow rate of 1.5 μL/min until 24 h. The PD studies were conducted over 24 h based on 10 intermittent dosing regimens and total daily doses ranged from 0.25 to 4 mg/kg and dosage intervals included 12 and 24 h. The lung tissue was collected after 24 h of treatment and homogenized for bacterial counts. The relationships between PK/PD parameters derived from lung dialysates and drug efficacy were analyzed using an inhibitory sigmoid Emax model. The percentage of time the free drug concentration exceeded the minimum inhibitory concentration (%fT > MIC) was the PK/PD index best describing the antimicrobial activity (R2 = 0.96) in the porcine experimental infection model. The %fT > MIC values required to achieve net bacterial stasis, 1, 2 and 3 log10 CFU/g reductions in the lung were 22.45, 28.86, 37.62, and 56.46%, respectively. Cefquinome exhibited time-dependent characteristics against A. pleuropneumoniae in vivo. These results provide valuable insights into the application of microdialysis in PK/PD integration model studies and optima regimen of cefquinome for the treatment of porcine respiratory diseases caused by A. pleuropneumoniae.

Optimizing tylosin dosage for co-infection of Actinobacillus pleuropneumoniae and Pasteurella multocida in pigs using pharmacokinetic/pharmacodynamic modeling

Formulating a therapeutic strategy that can effectively combat concurrent infections of Actinobacillus pleuropneumoniae (A. pleuropneumoniae) and Pasteurella multocida (P. multocida) can be challenging. This study aimed to 1) establish minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), time kill curve, and post-antibiotic effect (PAE) of tylosin against A. pleuropneumoniae and P. multocida pig isolates and employ the MIC data for the development of epidemiological cutoff (ECOFF) values; 2) estimate the pharmacokinetics (PKs) of tylosin following its intramuscular (IM) administration (20 mg/kg) in healthy and infected pigs; and 3) establish a PK-pharmacodynamic (PD) integrated model and predict optimal dosing regimens and PK/PD cutoff values for tylosin in healthy and infected pigs. The MIC of tylosin against both 89 and 363 isolates of A. pleuropneumoniae and P. multocida strains spread widely, ranging from 1 to 256 μg/mL and from 0.5 to 128 μg/mL, respectively. According to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) ECOFFinder analysis ECOFF value (≤64 µg/mL), 97.75% (87 strains) of the A. pleuropnumoniae isolates were wild-type, whereas with the same ECOFF value (≤64 µg/mL), 99.72% (363 strains) of the P. multicoda isolates were considered wild-type to tylosin. Area under the concentration time curve (AUC), T1/2, and Cmax values were significantly greater in healthy pigs than those in infected pigs (13.33 h × μg/mL, 1.99 h, and 5.79 μg/mL vs. 10.46 h × μg/mL, 1.83 h, and 3.59 μg/mL, respectively) (p < 0.05). In healthy pigs, AUC24 h/MIC values for the bacteriostatic activity were 0.98 and 1.10 h; for the bactericidal activity, AUC24 h/MIC values were 1.97 and 1.99 h for A. pleuropneumoniae and P. multocida, respectively. In infected pigs, AUC24 h/MIC values for the bacteriostatic activity were 1.03 and 1.12 h; for bactericidal activity, AUC24 h/MIC values were 2.54 and 2.36 h for A. pleuropneumoniae and P. multocida, respectively. Monte Carlo simulation lead to a 2 μg/mL calculated PK/PD cutoff. Managing co-infections can present challenges, as it often demands the administration of multiple antibiotics to address diverse pathogens. However, using tylosin, which effectively targets both A. pleuropneumoniae and P. multocida in pigs, may enhance the control of bacterial burden. By employing an optimized dosage of 11.94-15.37 mg/kg and 25.17-27.79 mg/kg of tylosin can result in achieving bacteriostatic and bactericidal effects in 90% of co-infected pigs.

Phenylbutazone concentrations in synovial fluid following administration via intravenous regional limb perfusion in the forelimbs of six adult horses

Background

Pain management is critical to equine welfare with non-steroidal anti-inflammatory drugs (NSAID) commonly used in horses. However, systemic NSAID use is limited by harmful gastrointestinal and renal side effects. Intravenous regional limb perfusion (IVRLP) is a technique used in horses that produces high, local antibiotic concentrations while limiting systemic circulation. NSAID-IVRLP would be a novel method of local pain management while limiting systemic NSAID side effects. To date, NSAID-IVRLP administration has not been reported in horses. This study aimed to identify the pharmacokinetics and local complications associated with using the NSAID phenylbutazone (PBZ) for IVRLP in six standing adult horses.

Methods

PBZ-IVRLP, at a dose of 2.2 mg/kg PBZ, was performed in a randomly assigned forelimb cephalic vein in 6 standing, healthy adult horses. A placebo-IVRLP was performed in the contralateral forelimb for comparison. Systemic serum and radiocarpal joint synovial fluid PBZ concentrations were identified at various timepoints (before IVRLP T-0 h, just after tourniquet removal T-0.5, 1.5, 3, 5, 12, 16, and 24 h post IVRLP) for non-compartmental pharmacokinetic analysis and concentration over time curves. Local complications associated with PBZ-IVRP were evaluated for up to 7 days following PBZ-IVRLP using physical and ultrasonographic assessment. On day 7 horses were humanely euthanized with histology performed on both forelimbs at PBZ-IVRLP and placebo-IVRLP administration sites.

Results

Non-compartmental pharmacokinetics for PBZ, and its major metabolite oxyphenbutazone (OBZ), were determined for serum and synovial fluid. Synovial PBZ concentrations (mean ± SD; 1.9 ± 2.1 μg/mL) were significantly lower (p = 0.03; CI,0.46-7.36) than serum PBZ concentrations (5.8 ± 5.1 μg/mL) at any time point. Physical and ultrasonographic measurements were not significantly different between PBZ- and placebo-IVRLP forelimbs. The most common histologic findings included focal deep dermal/subcutaneous hemorrhage and edema. Two horses showed perivasculitis and one horse showed a resolving thrombus in the cephalic vein of the PBZ-IVRLP limb. This horse also had severe perivasculitis and fibrinosuppurative dermatitis/panniculitis in the placebo-IVRLP limb.

Conclusion

PBZ-IVRLP pharmacokinetics at a 2.2 mg/kg dose showed no benefit compared to systemic PBZ administration in standing adult horses. Local complications associated with PBZ-IVRLP were similar to placebo-IVRLP on physical and ultrasonographic evaluation.

The dose regimen formulation of doxycycline hydrochloride and florfenicol injection based on ex vivo pharmacokinetic-pharmacodynamic modeling against the Actinobacillus pleuropneumoniae in pigs

Doxycycline hydrochloride and florfenicol combination (DoxHcl&FF) is an effective treatment for respiratory diseases. In the study, our objective was to evaluate the activity of DoxHcl&FF against Actinobacillus pleuropneumoniae (APP) in porcine pulmonary epithelial lining fluid (PELF) and the optimal dosage scheme to avoid the development of resistance. The DoxHcl&FF was administered intramuscularly (IM) at 20 mg/kg, and the PELF was collected at different time points. The minimum inhibitory concentration (MIC) and time-mortality curves were also included in the study. Based on the sigmoid Emax equation and dose equations, the study integrated the in vivo pharmacokinetic data of infected pigs and ex vivo pharmacodynamic data to obtain the area under concentration time curve (AUC0-24h)/MIC values in PELF and achieve bacteriostatic activity, bactericidal activity and the virtual eradication of bacteria. The study showed that the combination of DoxHcl and FF caused no significant changes in PK parameters. The peak concentration (Cmax) of FF in healthy and diseased pigs was 8.87 ± 0.08 μg/mL and 8.67 ± 0.07 μg/mL, the AUC0-24h were 172.75 ± 2.52 h·μg/mL and 180.22 ± 3.13 h·μg/mL, the Cmax of DoxHcl was 7.91 ± 0.09 μg/mL and 7.99 ± 0.05 μg/mL, and the AUC0-24h was 129.96 ± 3.70 h·μg/mL and 169.82 ± 4.38 h·μg/mL. DoxHcl&FF showed strong concentration-dependent tendencies. The bacteriostatic, bactericidal, and elimination activity were calculated as 5.61, 18.83 and 32.68 h, and the doses were 1.37 (bacteriostatic), 4.59 (bactericidal) and 7.99 (elimination) mg/kg. These findings indicated that the calculated recommended dose could assist in achieving more precise administration, increasing the effectiveness of DoxHcl&FF treatment for APP infections.

The pharmacokinetics and pharmacodynamics of cefquinome against Streptococcus agalactiae in a murine mastitis model

Cefquinome is a new generation cephalosporin that is effective in the treatment of mastitis in animals. In this study, we evaluated the associations between the specific pharmacokinetics and pharmacodynamics (PK/PD) of cefquinome and its antibacterial activity against Streptococcus agalactiae in a mouse model of mastitis. After a single intramammary dose of cefquinome (30, 60, 120, and 240 μg/mammary gland), the concentration of cefquinome in plasma was analysed by liquid chromatography with tandem mass spectrometry (HPLC/MS-MS). The PK parameters were calculated using a one-compartment first-order absorption model. Antibacterial activity was defined as the maximum change in the S. agalactiae population after each dose. An inhibitory sigmoid Emax model was used to evaluate the relationships between the PK/PD index values and antibacterial effects. The duration for which the concentration of the antibiotic (%T) remained above the minimum inhibitory concentration (MIC) was defined as the optimal PK/PD index for assessing antibacterial activity. The values of %T > MIC to reach 0.5-log10CFU/MG, 1-log10 CFU/MG and 2-log10 CFU/MG reductions were 31, 47, and 81%, respectively. When the PK/PD index %T > MIC of cefquinome was >81% in vivo, the density of the Streptococcus agalactiae was reduced by 2-log10. These findings provide a valuable understanding to optimise the dose regimens of cefquinome in the treatment of S. agalactiae infections.

Optimal Regimens and Clinical Breakpoint of Avilamycin Against Clostridium perfringens in Swine Based on PK-PD Study

Clostridium perfringens causes significant morbidity and mortality in swine worldwide. Avilamycin showed no cross resistance and good activity for treatment of C. perfringens. The aim of this study was to formulate optimal regimens of avilamycin treatment for C. perfringens infection based on the clinical breakpoint (CBP). The wild-type cutoff value (CO_WT) was defined as 0.25 μg/ml, which was developed based on the minimum inhibitory concentration (MIC) distributions of 120 C. perfringens isolates and calculated using ECOFFinder. Pharmacokinetics–pharmacodynamics (PK-PD) of avilamycin in ileal content were analyzed based on the high-performance liquid chromatography method and WinNonlin software to set up the target of PK/PD index (AUC_0–24h/MIC)_ex based on sigmoid E_max modeling. The PK parameters of AUC_0–24h, C_max, and T_max in the intestinal tract were 428.62 ± 14.23 h μg/mL, 146.30 ± 13.41 μg/ml,, and 4 h, respectively. The target of (AUC_0–24h/MIC)_ex for bactericidal activity in intestinal content was 36.15 h. The PK-PD cutoff value (CO_PD) was defined as 8 μg/ml and calculated by Monte Carlo simulation. The dose regimen designed from the PK-PD study was 5.2 mg/kg mixed feeding and administrated for the treatment of C. perfringens infection. Five respective strains with different MICs were selected as the infection pathogens, and the clinical cutoff value was defined as 0.125 μg/ml based on the relationship between MIC and the possibility of cure (POC) following nonlinear regression analysis, CART, and “Window” approach. The CBP was set to be 0.25 μg/ml and selected by the integrated decision tree recommended by the Clinical Laboratory of Standard Institute. The formulation of the optimal regimens and CBP is good for clinical treatment and to control drug resistance.

Modelling the antimicrobial pharmacodynamics for bacterial strains with versus without acquired resistance to fluoroquinolones or cephalosporins

OBJECTIVES

Antimicrobial resistance threatens therapeutic options for human and animal bacterial diseases worldwide. Current antimicrobial treatment regimens were designed against bacterial strains that were fully susceptible to them. To expand the useable lifetime of existing antimicrobial drug classes by modifying treatment regimens, data are needed on the antimicrobial pharmacodynamics (PD) against strains with reduced susceptibility. In this study, we generated and mathematically modelled the PD of the fluoroquinolone ciprofloxacin and the cephalosporin ceftriaxone against non-typhoidal Salmonella enterica subsp. enterica strains with varying levels of acquired resistance.

METHODS

We included Salmonella strains across categories of reduced susceptibility to fluoroquinolones or cephalosporins reported to date, including isolates from human infections, food-animal products sold in retail, and food-animal production. We generated PD data for each drug and strain via time-kill assay. Mathematical models were compared in their fit to represent the PD. The best-fit model's parameter values across the strain susceptibility categories were compared.

RESULTS

The inhibitory baseline sigmoid I_max (or E_max) model was best fit for the PD of each antimicrobial against a majority of the strains. There were statistically significant differences in the PD parameter values across the strain susceptibility categories for each antimicrobial.

CONCLUSION

The results demonstrate predictable multiparameter changes in the PD of these first-line antimicrobials depending on the Salmonella strain's susceptibility phenotype and specific genes conferring reduced susceptibility. The generated PD parameter estimates could be used to optimise treatment regimens against infections by strains with reduced susceptibility.

Systematic Review of the Pharmacological Evidence for the Selection of Antimicrobials in Bacterial Infections of the Central Nervous System in Dogs and Cats

Bacterial meningitis in dogs and cats is a rare disease associated with a high lethality rate. The spectrum of causative bacteria includes a diverse set of gram positive, gram negative and anaerobic species. Currently, no veterinary medicinal product is approved for this indication in these species in Europe. The objective of this review was to collect the available pharmacokinetic data for antibiotics approved in dogs and cats to enable a preliminary analysis of their potential effectiveness for the treatment of bacterial meningitis. This analysis yielded data for 13 different antibiotics in dogs and two in cats. Additionally, data about frequently recommended cephalosporines not approved in dogs and cats were included. The collected data was used to assess the potential of the respective antibiotics to attain certain simple pharmacokinetic-pharmacodynamic (PK-PD) indexes in the cerebrospinal fluid (CSF). A more sophisticated investigation using modern methods was not possible due to the limited data available. For this purpose, data about the sensitivity of four bacterial species commonly associated with meningitis in dogs and cats to these antibiotics were included. The analysis provided evidence for the potential effectiveness of ampicillin, doxycycline, enrofloxacin, ceftriaxone and cefoxitin against bacteria frequently detected in bacterial meningitis in dogs. Data were not available or insufficient for the assessment of several antibiotics, including frequently recommended substances like metronidazole and trimethoprim-sulphonamide. Little evidence is available for the use of antibiotics in cats afflicted with this disease, highlighting the need for further research to obtain data for evidence based therapeutic recommendations.

Is the suckling period and application pattern relevant for fluazuron against tick infestation in cows and their suckling calves?

Background

Fluazuron is a chitin synthesis inhibitor administered as a pour-on formulation in cattle for tick control. This study analyzes under endemic tick infestation, the incidence of the pour-on application pattern on the plasma levels of fluazuron in calves and cows in the lactation period of the beef cow. Two hundred and ninety-two beef cows around parturition were treated with a commercial pour-on formulation of fluazuron at a rate of 2.5 mg/kg of body weight. A total of 4 treatments were carried out on days 0, 32, 77, and 117. At each administration time, the cows were grouped according to the pour-on administration pattern: long (~ 60 cm pour-on application surface) and short (~ 30 cm pour-on application surface). Fluazuron levels in cows and calves plasma were determined before the third and fourth application for each subgroup (n = 10) by HPLC-MS/MS. During the entire study, cow-calf pairs were maintained under field conditions and qualitatively examined for tick infestation on the day of each treatment. Both treatments (long and short) schemes were designed to prevent the annual persistence of ticks.

Results

No animals with presence of ticks were identified during the first 117 days of the study, except for three cows and one calf at the time of the third application (day 77). There were no differences after 40 days (day 77) post-treatment of the second application (30 ± 5 ppb vs. 28.5 ± 12 ppb, p > 0.05) and 45 days (day 117) after the third application (147 ± 55 ppb vs 140 ± 46 ppb, p > 0.05) between groups of cows treated with the long or short pour-on application, respectively. Plasma concentration of fluazuron at second and third application was increased (3.3 and 2.9 times, respectively) in calves under free suckling compared to cows. Nevertheless, both groups of cows and calves showed a significant increase in plasma concentration of fluazuron between times (4.9 times, p < 0.0001 and 2.8 times, p < 0.0001, respectively). In both groups, tick prevalence was 0% throughout the trial, except for day 77, which reached 1%.

Conclusions

The main conclusions of this study were the following: 1) Different administration patterns (long vs. short) did not differ in plasma levels of fluazuron.; 2) Given that only the cows were treated and lactating calves presented higher plasma levels of fluazuron than cows, passage through milk appears to be relevant and possibly due to a cumulative effect and continuous drug intake.

Disposition of Cefquinome in Turkeys (Meleagris gallopavo) Following Intravenous and Intramuscular Administration

The bioavailability and pharmacokinetics in turkeys of cefquinome (CFQ), a broad-spectrum 4th-generation cephalosporin antibiotic, were explored after a single injection of 2 mg/kg body weight by intravenous (IV) and intramuscular (IM) routes. In a crossover design and 3-weeks washout interval, seven turkeys were assigned for this objective. Blood samples were collected prior to and at various time intervals following each administration. The concentration of CFQ in plasma was measured using HPLC with a UV detector set at 266 nm. For pharmacokinetic analysis, non-compartmental methods have been applied. Following IV administration, the elimination half-life (t_1/2ʎz), distribution volume at steady state (Vd_ss), and total body clearance (Cl_tot) of CFQ were 1.55 h, 0.54 L/kg, and 0.32 L/h/kg, respectively. Following the IM administration, CFQ was speedily absorbed with an absorption half-life (t_1/2ab) of 0.25 h, a maximum plasma concentration (C_max) of 2.71 μg/mL, attained (T_max) at 0.56 h. The bioavailability (F) and in vitro plasma protein binding of CFQ were 95.56% and 11.5%, respectively. Results indicated that CFQ was speedily absorbed with a considerable bioavailability after IM administration. In conclusion, CFQ has a favorable disposition in turkeys that can guide to estimate optimum dosage regimes and eventually lead to its usage to eradicate turkey's susceptible bacterial infections.

Antibacterial activity of combined aditoprim and sulfamethoxazole against Escherichia coli from swine and a dose regimen based on pharmacokinetic-pharmacodynamic modeling

The mortality of livestock caused by pathogenic Escherichia coli (E. coli) still accounts for a large proportion of deaths in large-scale production and reproduction, which causes devastating economic losses to the pig breeding industry. The aims of this study were to investigate the antibacterial activity of combined aditoprim (ADP) and sulfamethoxazole (SMZ) against clinical isolates of E. coli from pigs and to develop a pharmacokinetic-pharmacodynamic (PK-PD) model to formulate the optimal dose of ADP/SMZ for the treatment of pig colibacillosis. Blood and ileum fluid samples were collected at different times after single intramuscular injection of ADP/SMZ (5/25 mg/kg b.w.) to healthy pigs and E. coli-infected pigs. Concentrations of ADP and SMZ in plasma and ileum fluid were analyzed by HPLC. The peak concentration (C_max ) and the area under the concentration-time curve (AUC_0-24h ) in ileum fluid of healthy pigs were 1.76 ± 0.27 µg/ml and 18.92 ± 2.87 µg·h/ml for ADP and 19.15 ± 2.63 µg/ml and 125.70 ± 11.86 µg·h/ml for SMZ, respectively. C_max and AUC_0-24h in ileum fluid of infected pigs were 1.88 ± 0.13 µg/ml and 15.12 ± 0.75 µg·h/ml for ADP and 19.71 ± 3.68 µg/ml and 133.92 ± 17.14 µg·h/ml for SMZ, respectively. The minimum inhibitory concentrations (MICs) of combined ADP and SMZ (ADP/SMZ) against 185 strains of E. coli from pigs were determined. The MIC₅₀ and MIC₉₀ of ADP/SMZ were 0.5/2.5 and 4/20 µg/ml, respectively. The MIC of the selected pathogenic E. coli SHC28 was 0.5/2.5 µg/ml in Mueller-Hinton broth and 0.25/1.25 µg/ml in ileum fluid, respectively. In vitro, the mutant prevention concentration, the post-antibiotic effect, growth, and time-killing curves in vitro and ex vivo of ADP/SMZ against the isolate SHC28 were assayed for PD studies. The results showed that ADP/SMZ exhibited strong concentration-dependent antimicrobial activity against E. coli. After integrating the in vivo pharmacokinetic parameters of infected pigs and ex vivo PD data using the sigmoid E_max (Hill) equation, the AUC_24h /MIC values in ileum fluid for bacteriostatic, bactericidal, and bacterial eradication were 18.84, 65.39, and 110.68 h, respectively. In conclusion, a dosage of 3.45/17.25 mg/kg ADP/SMZ by intramuscular injection daily for 3 consecutive days may be sufficient to treat swine colibacillosis due to E. coli with a MIC of 0.5/2.5 µg/ml.

Co-formulation of ketoprofen with tulathromycin alters pharmacokinetic and pharmacodynamic profile of ketoprofen in cattle

The current studies aimed to evaluate the pharmacokinetic (PK) and pharmacodynamic (PD) profile and to establish a PK-PD model for ketoprofen in a new fixed combination product containing tulathromycin (2.5 mg/kg) and ketoprofen (3 mg/kg) to treat bovine respiratory disease associated with pyrexia in cattle. Firstly, the effect of different ketoprofen doses as mono-substance (1, 3, and 6 mg/kg subcutaneous) on lipopolysaccharide-induced fever was evaluated which indicated that rectal temperature reduction lasted longer in the calves receiving 3 and 6 mg/kg ketoprofen. Secondly, the PK profile of the combination product was compared with mono-substance products (3 mg/kg subcutaneous and intramuscular). The PK profile of ketoprofen in the combination product was characterized by longer t_1/2 , lower C_max and increased AUC in comparison with mono-substance products. Due to prolonged ketoprofen exposure in the combination product, the pyrexia reducing effect of the combination product lasted longer in a second lipopolysaccharide challenge study in comparison with mono-substance products. Finally, a PK-PD model for the anti-pyretic effect of ketoprofen was developed based on the data from the different studies. The PK-PD model eliminated the need for additional animal experiments and indicated that a 3 mg/kg ketoprofen dose in the combination product provided optimal efficacy.

Nonlinear Mixed-Effect Pharmacokinetic Modeling and Distribution of Doxycycline in Healthy Female Donkeys after Multiple Intragastric Dosing-Preliminary Investigation

Doxycycline (DXC) is a broad-spectrum antibacterial antimicrobial administered to horses for the treatment of bacterial infections which may also affect donkeys. Donkeys have a different metabolism than horses, leading to differences in the pharmacokinetics of drugs compared to horses. This study aimed to describe the population pharmacokinetics of DXC in donkeys. Five doses of DXC hyclate (10 mg/kg) were administered via a nasogastric tube, q12 h, to eight non-fasted, healthy, adult jennies. Serum, urine, synovial fluid and endometrium were collected for 72 h following the first administration. Doxycycline concentration was measured by competitive enzyme immunoassay. Serum concentrations versus time data were fitted simultaneously using the stochastic approximation expectation-maximization algorithm for nonlinear mixed effects. A one-compartment model with linear elimination and first-order absorption after intragastric administration, best described the available pharmacokinetic data. Final parameter estimates indicate that DXC has a high volume of distribution (108 L/kg) as well as high absorption (10.3 h^-1) in donkeys. However, results suggest that oral DXC at 10 mg/kg q12 h in donkeys would not result in a therapeutic concentration in serum, urine, synovial fluid or endometrium by comparison to the minimum inhibitory concentration of common equine pathogens. Further studies are recommended to identify appropriate dosage and dosing intervals of oral DXC in donkeys.

Pharmacokinetics and pharmacodynamics of enrofloxacin treatment of Escherichia coli in a murine thigh infection modeling

BACKGROUND

Enrofloxacin is an antibacterial drug with broad-spectrum activity that is widely indicated for veterinary use. We aim to develop the clinical applications of Enrofloxacin against colibacillosis by using the neutropenic mice thigh infection model.

RESULTS

The minimum inhibitory concentration (MIC) distribution of 67 isolated E. coli strains to ENR was calculated using CLSI guidelines. Whereas, the MIC₅₀ value calculation was considered as the population PD parameter for ENR against E. coli strains. The MIC values of 15 E. coli strains were found to be nearest to the MIC₅₀ i.e., 0.25 μg/mL. Of all the tested strains, the PK-PD and E. coli disease model was established via selected E. coli strain i.e., Heilong 15. We analyzed the PK characteristics of ENR and its metabolite ciprofloxacin (CIP) following a single subcutaneous (s.c.) injection of ENR (1.25, 2.5, 5, 10 mg/kg). The concentration-time profiling of ENR within the plasma specimens was determined by considering the non-compartmental analysis (NCA). The basic PK parameters of ENR for the peak drug concentration (C_max) and the area under the concentration-time curve (AUC) values were found to be in the range of 0.27-1.97 μg/mL and 0.62-3.14 μg.h/mL, respectively. Multiple s.c. injection over 24 h (1.25, 2.5, 5, 10 mg/kg at various time points i.e., 6, 8, 12, and 24 h respectively) were administered to assess the targeted PD values. The Akaike Information Criterion (AIC) was used to choose PD models, and the model with the lowest AIC was chosen. The inhibitory E_max model was employed to calculate the related PK-PD parameters. The results of our study indicated that there was a strong correlation between the AUC/MIC and various antibacterial activities (R² = 0.9928). The target values of dividing AUC/MIC by 24 h for bacteriostatic action were 1-log10 reduction, 2-log10 reduction, and 3-log10 reduction 0.325, 0.4375, 0.63, and 0.95 accordingly.

CONCLUSION

The identified pharmacodynamics targets for various antibacterial effects will be crucial in enhancing ENR clinical applications and serving as a key step in reducing bacterial resistance.

Pharmacokinetics and pharmacodynamics of doxycycline in a Streptococcusequi subsp. zooepidemicus infection model in horses

The objectives of this study were to investigate the pharmacokinetics (PK), pharmacodynamics (PD), and the efficacy of oral administration of doxycycline (DXC) in horses with Streptococcus zooepidemicus tissue infections. Tissue chambers (TC) were implanted subcutaneously in the cervical region of 7 horses and inoculated with a single S. zooepidemicus isolate with a minimum inhibitory concentration (MIC) of 0.25 µg/ml, determined by agar dilution. Doxycycline hyclate (10 mg/kg, orally, q 12 h, for 5 days) mixed with poloxamer gel was started following inoculation. The TC fluid was sampled prior to and following inoculation for cytology analysis, quantitative culture, and DXC determination. Plasma DXC concentrations were measured over 48 h following the last dose of DXC administered. The mean plasma peak concentration (C_max ) of DXC was 0.32 µg/ml, and concentrations above the MIC were only reached in 3 TC samples. In plasma, mean T > MIC was 2.4 h, mean C_max /MIC was 1.30, and mean AUC_last /MIC was 11.63 h. These PK/PD indices did not reach the suggested targets for DXC treatments of infections, and the TC abscessed in all horses. This is the first study to evaluate the recommended dose of DXC in horse in an infection model.

Pharmacokinetic evaluation of roxithromycin and ciprofloxacin in treating complicated avian mycoplasmosis in broiler chickens

The use of roxithromycin along with ciprofloxacin is having potential to be a promising antimicrobial therapy to treat complicated avian mycoplasmosis in broiler chickens. The present research was undertaken to study the influence of roxithromycin (20 mg/kg body weight) and ciprofloxacin (10 mg/kg body weight) on the oral pharmacokinetics of each other, when both drugs are concomitantly administered in eight healthy male broiler chickens (n=8) and to establish their therapeutic dosage regimens. Their plasma concentrations were assayed by validated ultra high performance liquid chromatography (UHPLC) methods using UV detector. Oral pharmacokinetic parameters were calculated from plasma concentration versus time data based on non-compartmental analysis. Statistically, plasma roxithromycin concentration was significantly higher at one time point only (0.5 h) and plasma ciprofloxacin concentration was significantly lower at the time point of 2 h only when used in combination, in comparison to their respective values obtained after their alone administrations. The pharmacokinetic parameters of roxithromycin and ciprofloxacin showed no significant effect on values of either drug when given in combination and there was a lack of pharmacokinetic interaction between the two antimicrobials. The predicted effective oral dose rate of roxithromycin was 20 mg/kg body weight, every 12 h, and that of ciprofloxacin was 10 mg/kg body weight, every 24 h, to treat complicated avian mycoplasmosis in broiler chickens.

Pharmacokinetics and Pharmacodynamics of Immediate- and Modified-Release Mycophenolic Acid Preparations in Healthy Beagle Dogs

Background: Mycophenolic acid (MPA) is a broad-acting immunomodulating agent that may be therapeutically beneficial for the treatment of immune-mediated diseases in canine patients.

Objectives: To determine the suppressive effects of MPA on T-cell proliferation, and to assess the feasibility of a canine-specific q24 h modified-release MPA formulation (OKV-1001b).

Animals: Fifteen healthy purpose-bred male beagle dogs.

Methods: Two nearly identical open-label fifteen-day studies were conducted in which dogs were randomized to receive mycophenolate mofetil (MMF; 10 mg/kg q12h), or two doses of OKV-1001b (270 mg and 180 mg; q24h). Serial pharmacokinetic (PK) and pharmacodynamic (PD) samples were collected on Days 1, 8, and 15. MPA plasma concentrations were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS), while an ex vivo T-cell proliferation assay assessed PD effects. Dogs were continuously monitored for evidence of side effects and gastrointestinal tolerability.

Results: MPA induced inhibition of T-cell proliferation was observed following administration of all MPA preparations in a clear concentration-dependent manner. The PK/PD relationship was maintained across all days and time-points. Data generated herein suggest that MPA plasma concentrations above 600 ng/mL achieve at least 50% inhibition of T-cell proliferation.

Conclusions and Clinical Importance: MPA holds therapeutic potential for treating dogs with immune-mediated disease, but clinical trials will be necessary to determine its safety and efficacy in naturally occurring disease. Likewise, q24h oral modified release MPA preparations that maintain MPA plasma concentrations between 600 and 1,000 ng/mL are warranted for further studies in client-owned dogs.

Pharmacokinetics of levofloxacin in non-lactating goats and evaluation of drug effects on resistance in coliform rectal flora

This study aimed to evaluate the pharmacokinetics/pharmacodynamics (PK/PD) of levofloxacin in non-lactating goats. Using a randomized cross-over study design, each group of animals (n = 7) received 2 mg/kg of levofloxacin intravenously (IV) and subcutaneously (SC). Plasma concentrations of levofloxacin were quantified by High Performance Liquid Chromatography with fluorescence detector (HPLC-FL). Rectal swabs were collected prior and after the treatment to identify the main bacterial population and to evaluate in vitro antimicrobial susceptibility using minimal inhibitory concentration (MIC) method. Mean values of terminal half-life for IV and SC groups were 4.56 and 5.14 h, respectively. After SC administration, the peak plasma concentration was achieved at 2 h, with a C_max of 3681 ng/mL. Mean bioavailability was 92.12%. Bacteria isolation showed the presence of Escherichia coli (E. coli) that quickly becomes resistant to levofloxacin potentially rendering the drug ineffective. Results seem to suggest that levofloxacin is able to reach considerable plasma concentrations after both IV and SC administration, but it must be considered that both routes of administration can lead to a reversible selection of resistance in gastro-intestinal bacteria.

Mathematical modeling of the 'inoculum effect': six applicable models and the MIC advancement point concept

Antimicrobial treatment regimens against bacterial pathogens are designed using the drug's minimum inhibitory concentration (MIC) measured at a bacterial density of 5.7 log₁₀(colony-forming units (CFU)/mL) in vitro. However, MIC changes with pathogen density, which varies among infectious diseases and during treatment. Incorporating this into treatment design requires realistic mathematical models of the relationships. We compared the MIC–density relationships for Gram-negative Escherichia coli and non-typhoidal Salmonella enterica subsp. enterica and Gram-positive Staphylococcus aureus and Streptococcus pneumonia (for n = 4 drug-susceptible strains per (sub)species and 1–8 log₁₀(CFU/mL) densities), for antimicrobial classes with bactericidal activity against the (sub)species: β-lactams (ceftriaxone and oxacillin), fluoroquinolones (ciprofloxacin), aminoglycosides (gentamicin), glycopeptides (vancomycin) and oxazolidinones (linezolid). Fitting six candidate mathematical models to the log₂(MIC) vs. log₁₀(CFU/mL) curves did not identify one model best capturing the relationships across the pathogen–antimicrobial combinations. Gompertz and logistic models (rather than a previously proposed Michaelis–Menten model) fitted best most often. Importantly, the bacterial density after which the MIC sharply increases (an MIC advancement-point density) and that density's intra-(sub)species range evidently depended on the antimicrobial mechanism of action. Capturing these dependencies for the disease–pathogen–antimicrobial combination could help determine the MICs for which bacterial densities are most informative for treatment regimen design.

Murine Thigh Microdialysis to Evaluate the Pharmacokinetic/Pharmacodynamic Integration of Cefquinome Against Actinobacillus pleuropneumoniae

This study aimed to explore the application of microdialysis in pharmacokinetic (PK)/pharmacodynamic (PD) integration of cefquinome against Actinobacillus pleuropneumoniae. After the A. pleuropneumoniae population reached 10⁶ CFU/thigh, the mice received 0.04, 0.16, 0.63, 2.5, and 10 mg/kg cefquinome by subcutaneous injection. Plasma samples were collected by retro-orbital puncture for 4 h, and thigh dialysate was obtained by microdialysis at a flow rate of 1.5 μL/min for 6 h for the PK study. For the PD experiment, the infected mice were treated with a 4-fold-increase in the total cefquinome dose, ranging from 0.01 to 10 mg/kg/24 h, divided into one, two, three, four, and eight doses. The number of bacteria was determined and an inhibitory sigmoid maximum effect (E_max) model was used to analyse the relationships between PK/PD parameters and efficacy. The mean penetration of cefquinome from plasma to the thigh was 0.591. The PK data for PK/PD integration were obtained by extrapolation. The fittest PK/PD parameter for efficacy evaluation was %fT>MIC (the percentage of time that free drug concentrations exceed the MIC). The magnitudes of %fT>MIC to achieve net bacterial stasis, 1-log₁₀ CFU reduction, 2-log₁₀ CFU reduction, and 3-log₁₀ CFU reduction were 19.56, 28.65, 41.59, and 67.07 % in plasma and 21.74, 36.11, 52.96, and 82.68% in murine thigh, respectively. Microdialysis was first applied to evaluate the PK/PD integration of cefquinome against A. pleuropneumoniae. These results would provide valuable references when we apply microdialysis to study the PK/PD integration model and use cefquinome to treat animal diseases caused by A. pleuropneumoniae.

Pharmacokinetics and tissue disposition of enrofloxacin in rainbow trout after different routes of administration

Plasma pharmacokinetics (PK) and tissue disposition of enrofloxacin (EFX) was studied in rainbow trout (Oncorhynchus mykiss) after a single oral administration of 10 mg/kg, and by immersion baths of 20 ppm during 2.5 h and 100 ppm during 0.5 h, at water temperature of 16.3 ± 0.3 °C.Concentrations of EFX in plasma and tissues (skin, muscle, liver, kidney and gut) were determined using high performance liquid chromatography (HPLC) with fluorescence detection.Pharmacokinetic parameters were analyzed with a non-compartmental model. After oral administration, t½β, AUC and AUC_tissues/AUC_plasma ratio were 42.98 h, 21.80μg-h/ml and ≤ 18.63, respectively.After immersion baths of 20 ppm during 2.5 h and 100 ppm during 0.5 h, the t½β, AUC and AUC_tissues/AUC_plasma were 42.77 and 44.67, 9.83 and 12.83 μg-h/ml and ≤ 9.81 and ≤ 7.13, respectively.Therefore, oral (10 mg/kg) and bath administration in rainbow trout can provide AUC/MIC of ≥125 and Cmax/MIC of ≥10 to treat diseases caused by susceptible bacteria with MIC ≤ 0.04 μg/ml. This information can be helpful for the right use of EFX in rainbow trout. Also, this is the first study that determines the antibiotic tissue disposition in rainbow trout by using different administration routes.

Effect of supportive therapy on the pharmacokinetics of intravenous marbofloxacin in endotoxemic sheep

The purpose of this study was to determine the influences of supportive therapy (ST) on the pharmacokinetics (PK) of marbofloxacin in lipopolysaccharide (LPS)-induced endotoxemic sheep. Furthermore, minimum inhibitory concentration (MIC) of marbofloxacin against Escherichia coli, Mannheimia haemolytica, Pasteurella multocida, Klebsiella pneumoniae, Salmonella spp., and Staphylococcus aureus was determined. The study was performed using a three-period cross PK design following a 15-day washout period. In the first period, marbofloxacin (10 mg/kg) was administered by an intravenous (IV) injection. In the second and third periods, marbofloxacin was co-administered with ST (lactated ringer + 5% dextrose + 0.45% sodium chloride, IV, 20 ml/kg, dexamethasone 0.5 mg/kg, SC) and ST + LPS (E. coli O55:B5, 10 µg/kg), respectively. Plasma marbofloxacin concentration was measured using HPLC-UV. Following IV administration of marbofloxacin alone, the t 1 / 2 λ z , AUC_0-∞ , Cl_T , and V_dss were 2.87 hr, 34.73 hr × µg/ml, 0.29 L hr^-1  kg^-1 , and 0.87 L/kg, respectively. While no change was found in the MBX + ST group in terms of the PK parameters of marbofloxacin, it was determined that the Cl_T of marbofloxacin decreased, AUC_0-∞ increased, and t 1 / 2 λ z and MRT prolonged in the MBX + ST + LPS group. MIC values of marbofloxacin were 0.031 to >16 µg/ml for E. coli, 0.016 to >16 µg/ml for M. haemolytica, 0.016-1 µg/ml for P. multocida, 0.016-0.25 µg/ml for K. pneumoniae, 0.031-0.063 µg/ml for Salmonella spp., and 0.031-1 µg/ml for S. aureus. The study results show the necessity to make a dose adjustment of marbofloxacin following concomitant administration of ST in endotoxemic sheep. Also, the PK and pharmacodynamic effect of marbofloxacin needs to be determined in naturally infected septicemic sheep following concomitant administration of single and ST.

Antibacterial activity of cyadox against Clostridium perfringens in broilers and a dosage regimen design based on pharmacokinetic-pharmacodynamic modeling

Necrotic enteritis is an intestinal disease caused by Clostridium perfringens (C. perfringens) that results in high economic losses to the poultry industry. The purpose of this study was to investigate the antibacterial activity of cyadox against C. perfringens and to formulate its dosage regimen based on pharmacokinetics/pharmacodynamics (PK/PD) modeling in broilers. The PK parameters of cyadox in ileum of healthy and infected broilers following oral administration at 30 mg/kg body weight (BW) were investigated and PD study the MIC, MBC, MPC, and PAE were determined. The time-killing curves were established in vitro and ex vivo to evaluate the antibacterial activity of cyadox against C. perfringens. The results revealed that the MIC of cyadox against C. perfringens was 1-16 μg/mL. After oral administration of cyadox, the peak concentration (C_max), maximum concentration time (T_max), and area under the concentration-time curve (AUC) in ileum content of broilers were 143.55-161.48 μg/mL, 1.08-1.25 h, and 359.51-405.69 μg h/mL respectively. After Integrating the in vivo PK and ex vivo PD data the AUC_24h/MIC values needed for bacteriostatic, bactericidal and bacterial eradication were 27.71 h, 78.93 h, and 165.14 h, respectively. By model validation, the cure rate was 85.71%. In conclusion, a dosage regimen of 14.02 mg/kg repeated after every 12 h for 3-5days was expected to be therapeutically effective in broilers against C. perfringens with MIC ≤2 μg/mL.

Pharmacokinetics and pharmacodynamics of olopatadine following administration via nasogastric tube to healthy horses

OBJECTIVE

To investigate the pharmacokinetics and antihistaminic effects (pharmacodynamics) of olopatadine in a small population of healthy horses after administration via nasogastric tube.

ANIMALS

4 healthy adult Thoroughbreds.

PROCEDURES

Olopatadine (0.1 mg/kg, once) was administered via nasogastric tube. Blood samples were collected at predetermined time points for pharmacokinetic analyses of the drug in plasma. Olopatadine effects were investigated by measurement of cutaneous wheals induced by ID histamine injection (0.1 mL [10 μg]/injection) at predetermined time points. Inhibition effect ratios were calculated on the basis of measured wheal size (area) after versus before olopatadine administration.

RESULTS

Mean ± SD maximum plasma olopatadine concentration was 48.8 ± 11.0 ng/mL approximately 1.5 hours after administration. Median terminal half-life was 6.11 hours. Mean ± SD maximal effect was 88.2 ± 4.9% inhibition approximately 3.5 hours after drug delivery, and the inhibition effect remained > 80% for 12.5 hours after treatment. No signs of adverse clinical effects were observed.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested olopatadine may have a strong, long-term inhibitory effect against histamine-induced wheals in the skin of horses. Clinical research with a larger number of horses is warranted.

Pharmacokinetic-pharmacodynamic modelling for the determination of optimal dosing regimen of florfenicol in Nile tilapia (Oreochromis niloticus) at different water temperatures and antimicrobial susceptibility levels

Optimized dosing regimen is key to the effective use of antibacterials and to minimizing drug-related side effects. The current study established a pharmacokinetic-pharmacodynamic (PK-PD) model for the determination of optimal antibacterial dosing regimen in fish taken into consideration the temperature-dependent PK and the pathogen-dependent antimicrobial susceptibility, using florfenicol (FF) in Nile tilapia as an example. The calculated optimal dosages significantly varied by temperature and target MIC levels, ranging from 2.23 (MIC 1 µg/ml at 24°C) to 34.88 mg kg^-1  day^-1 (MIC 4 µg/ml at 32°C). The appropriateness of the calculated dosages was successfully verified by the in vivo studies. After 5 days of oral administration of the calculated optimal dosage at 24°C, the predicted plasma drug values were in line with the mean observed C_min(ss) while at 28 and 32°C underestimation of the C_min(ss) in a dose-dependent manner was observed and likely due to the occurrence of non-linear PK at high dosages. The averaged serum protein binding of FF was 19.1%. Our results demonstrated the appropriateness and clinical applicability of the developed PK-PD approach for the determination of optimal dosing regimens at given temperatures and MICs. Saturation metabolism and PK non-linearity of FF in tilapia warrant further study.

Pharmacokinetics of the amoxicillin-clavulanic acid combination after intravenous and oral administration in cats

The pharmacokinetic properties of amoxicillin (AMX) and clavulanic acid (CLV) were studied in healthy cats following single intravenous and oral dosage of 10 mg/kg of AMX and 2.5 mg/kg of CLV. The drug concentrations in plasma were determined by a high-performance liquid chromatographic-tandem mass spectrometry (LC-MS-MS) method validated for canine plasma and further subjected to noncompartmental analysis. After intravenous injection, no significant difference (p > 0.05) was found in the volume of distribution of these two compounds. In addition, AMX and CLV were both rapidly eliminated from plasma with a clearance of 0.453 and 0.921 L hr^-1  kg^-1 , respectively; however, a quicker elimination was observed for CLV (p < 0.01). After oral administration, both drugs were characterized by rapid absorption with an absorption half-life of 1.10 and 0.70 hr for AMX and CLV, respectively. Significant differences were observed between their absorption rates (p < 0.05). However, the oral bioavailabilities of AMX and CLV (75.57% and 98.15%, respectively) were not statistically different (p > 0.05). A total intravenous or oral dose at 12.5 mg/kg of AMX and CLV (4:1) is predicted to be effective for treating those bacterial species isolated from cats with a minimum inhibitory concentration (MIC) of ≤0.25 μg/ml for 12 hr, based on a time above the MIC (T > MIC) of 40%.

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.

Benefits of a multimodal analgesia compared to local anesthesia alone to alleviate pain following castration in sheep: a multiparametric approach

Castration of male ruminants is a common livestock management practice, but induces pain. However, little is known about the effectiveness of multimodal analgesia compared to local anesthesia (LA) alone in reducing pain associated with burdizzo castration in sheep. This study aimed to monitor the pain response induced by castration in sheep and to assess the efficacy of analgesia strategies. Twenty-four 12-month-old male Texel sheep were burdizzo-castrated after administration of physiological serum (Burd), local anesthetic (Burd+LA) or LA plus non-steroidal anti-inflammatory drug (Burd+LA+NSAID). Sheep responses were monitored using behavioral and physiological indices of pain. Sampling occurred from 24 h pre-castration to 78 h post-castration, split into four periods based on the duration of analgesia: P0 (T-24 to T-1 h), P1 (T0 to T+2 h), P2 (T+3 to T+32 h) and P3 (T+36 to T+78 h). Behavioral indices were attention and head position, ear position, position of the eyelid, other facial expression, standing/lying postures, postures of the legs, clinical signs and abnormal activities. Physiological indices consisted in indicators of inflammation (haptoglobin, serum amyloid A (SAA), body temperature), hypothalamo-pituitary-adrenal axis (cortisol, non-esterified fatty acids, glucose), autonomous nervous system (heart rate variability (HRV)) and oxidative stress. The variables contributing most to discrimination of the period×treatment groups were analyzed by factorial discrimination analysis. Pre-castration (P0), there was no significant difference between treatments for all indicators (P > 0.05). Post-castration, eight indicators varied significantly according to period and treatment: cortisol, clinical signs, ratio of low frequency/high frequency (LF/HF) bands of the HRV, attention and head position, SAA, haptoglobin, body temperature and glucose. The treatment×periods groups were well discriminated by the 23 indicators. Burd in P0, Burd+LA in P0 and Burd+LA+NSAID in P0, P1 and P2 had low values for all indicators, likely reflecting absence of pain and discomfort. Burd in P1 and P2 and Burd+LA in P2 showed clinical signs and reduced attention, high LF/HF and high cortisol levels, reflecting acute pain. Burd and Burd+LA in P3 had high temperature, high haptoglobin, high glucose and high SAA, but no response from other pathways. These results suggest that (i) behavioral signs of pain were apparent up to 32 h post-castration, (ii) LA was partially effective, but only during its time of action (2 h) and (iii). multimodal analgesia (LA and NSAID) was effective for up to 3 days post-castration. These findings, and especially those related to sheep behavior, can help veterinarians and farmers better detect pain and refine their pain alleviation methods.

Optimization of Antimicrobial Treatment to Minimize Resistance Selection

Optimization of antimicrobial treatment is a cornerstone in the fight against antimicrobial resistance. Various national and international authorities and professional veterinary and farming associations have released generic guidelines on prudent antimicrobial use in animals. However, these generic guidelines need to be translated into a set of animal species- and disease-specific practice recommendations. This article focuses on prevention of antimicrobial resistance and its complex relationship with treatment efficacy, highlighting key situations where the current antimicrobial drug products, treatment recommendations, and practices may be insufficient to minimize antimicrobial selection. The authors address this topic using a multidisciplinary approach involving microbiology, pharmacology, clinical medicine, and animal husbandry. In the first part of the article, we define four key targets for implementing the concept of optimal antimicrobial treatment in veterinary practice: (i) reduction of overall antimicrobial consumption, (ii) improved use of diagnostic testing, (iii) prudent use of second-line, critically important antimicrobials, and (iv) optimization of dosage regimens. In the second part, we provided practice recommendations for achieving these four targets, with reference to specific conditions that account for most antimicrobial use in pigs (intestinal and respiratory disease), cattle (respiratory disease and mastitis), dogs and cats (skin, intestinal, genitourinary, and respiratory disease), and horses (upper respiratory disease, neonatal foal care, and surgical infections). Lastly, we present perspectives on the education and research needs for improving antimicrobial use in the future.

In vivo pharmacokinetic/Pharmacodynamic modeling of Enrofloxacin against Escherichia coli in broiler chickens

Background

Systemic Escherichia coli infections cause early mortality of commercial broiler chickens. Although enrofloxacin has long been used in poultry, the in vivo pharmacokinetic/pharmacodynamic (PK/PD) relationship of enrofloxacin against E. coli is unclear. The present study aimed to establish an in vivo PK/PD model of enrofloxacin against E. coli in seven-day-old chicks and to ascertain whether the selection of target organ for PD determination is critical for parameter magnitude calculation in enrofloxacin PK/PD modeling.

Results

The in vivo effectiveness of enrofloxacin against E. coli in different organs varied, with the E_max ranging from − 4.4 to − 5.8 Log₁₀ colony forming units (cfu)/mL or cfu/g. Both the surrogate AUC_0–24/MIC of enrofloxacin or AUC_0–24/MIC of the combination of enrofloxacin and ciprofloxacin correlated well with effectiveness in each organ. The AUC_0–24/MIC ratio of the combination of enrofloxacin and ciprofloxacin producing bactericidal and elimination effects were 21.29 and 32.13 in blood; 41.68, and 58.52 in the liver; and 27.65 and 46.22 in the lung, respectively.

Conclusions

The in vivo effectiveness of enrofloxacin against E. coli in different organs was not identical after administration of the same dosage. To describe the magnitude of PK/PD parameter exactly, bacterial loading reduction in different organs as PD endpoints should be evaluated and compared in PK/PD modeling. The selection of a target organ to evaluate PDs is critical for rational dosage recommendation.

Pharmacokinetic-pharmacodynamic integration of marbofloxacin after single and repeated intravenous administration in goats

The single dose pharmacokinetics (PK) of marbofloxacin was compared with repeated intravenous (IV) administrations in six healthy goats at the dose rate of 2 mg/kg body weight at 24 h interval for 5 days. Blood samples were collected at times: 5, 15, 30 min and 1, 2, 4, 6, 9, 12, 24, 36, 48 and 72 h post drug administration. Plasma drug concentrations were determined by High Performance Liquid Chromatography and concentration-time data were subjected to non-compartment analysis. The MIC and MBC of marbofloxacin against Escherichia (E.) coli and Pasteurella (P.) multocida in Mueller Hinton Broth were determined by broth microdilution method. The t_1/2elm = 4.37 ± 0.18 h and Cl_B = 0.29 ± 0.01 following single administration were not significantly different from t_1/2elm = 5.11 ± 0.22 h and Cl_B = 0.26 ± 0.01 mL/kg/h after repeated administrations of marbofloxacin. Accumulation index (AI = 1.1) indicated no accumulation of marbofloxacin following repeated IV administrations up to 5 days. The respective MICs of marbofloxacin against E. coli and P. multocida were 0.03 μg/mL and 0.4 μg/mL. The AUC_0-24h/MIC ratios were 226.64 ± 7.21 h for E. coli and 16.99 ± 0.541 h for P. multocida. PK/PD integration indicated that marbofloxacin daily dose of 2 mg/kg is appropriate for treating E. coli (MIC ≤ 0.03 μg/mL) infections. However, a higher dose of 6 mg/kg/day is suggested to obtain clinical cure against diseases caused by P. multocida having MIC₉₀ = 0.12 μg/mL in goat species.

Pharmacokinetic/Pharmacodynamic Integration to Evaluate the Changes in Susceptibility of Actinobacillus pleuropneumoniae After Repeated Administration of Danofloxacin

To evaluate the relationship between pharmacokinetic/pharmacodynamic (PK/PD) parameters and changes in susceptibility and resistance frequency of Actinobacillus pleuropneumoniae CVCC 259, a piglet tissue cage (TC) infection model was established. After A. pleuropneumoniae populations maintained at 10⁸ CFU/mL in TCs, piglets were treated with various doses of danofloxacin once daily for 5 consecutive days by intramuscular injection. Both the concentrations of danofloxacin and the population of vial cells were determined. Changes in susceptibility and resistance frequency were monitored. Polymerase chain reaction (PCR) amplification of quinolone resistance-determining regions (QRDRs) and DNA sequencing were performed to identify point mutations in gyrA, gyrB, parC, and parE genes. Furthermore, the susceptibility of mutants to danofloxacin and enrofloxacin was determined in the presence or absence of reserpine to assess whether the mutants were caused by efflux pumps. The MICs and resistant frequency of A. pleuropneumoniae both increased when danofloxacin concentrations fluctuated between MIC₉₉ (0.05 μg/mL) and MPC (mutant prevention concentration, 0.4 μg/mL). As for PK/PD parameters, the resistant mutants were selected and enriched when AUC_24h/MIC₉₉ ranged from 34.68 to 148.65 h or AUC_24h/MPC ranged from 4.33 to 18.58 h. Substitutions of Ser-83→Tyr or Ser-83→Phe in gyrA and Lys-53→Glu in parC were observed. The susceptibility of mutants obtained via danofloxacin treatment at 1.25 and 2.5 mg/kg were less affected by reserpine. These results demonstrate that maintaining the value of AUC_24h/MPC above 18.58 h may produce a desirable antibacterial effect and protect against A. pleuropneumoniae resistance to danofloxacin.

Pharmacokinetic and Pharmacodynamic Properties of Rosmarinic Acid in Rat Cholestatic Liver Injury

The objective of this study was to evaluate the hepatoprotective and metabolic effects of rosmarinic acid (RA) in rats. RA [100 mg/kg body weight (BW)] was intragastrically (i.g.) administered to Sprague-Dawley (SD) rats once a day for seven consecutive days. The rats were then i.g. administered α-naphthylisothiocyanate (ANIT) (80 mg/kg once on the 5th day) to induce acute intrahepatic cholestasis after the last administration of RA. Blood samples were collected at different time points (0.083 h, 0.17 h, 0.33 h, 0.5 h, 0.75 h, 1 h, 1.5 h, 3 h, 4 h, 6 h, 8 h, 12 h, 20 h) after administration, and the levels of RA were estimated by HPLC. Plasma and bile biochemical analysis, bile flow rate, and liver histopathology were measured to evaluate the hepatoprotective effect of RA. The PK-PD curves showed obviously clockwise (AST and ALT) or anticlockwise (TBA, TBIL). Pretreatment with RA at different doses significantly restrained ANIT-induced pathological changes in bile rate, TBA, TBIL, ALT, AST (p < 0.05 or p < 0.01). The relationship between RA concentration and its hepatoprotective effects on acute cholestasis responses was assessed by PK-PD modeling.

Population variability in animal health: Influence on dose-exposure-response relationships: Part II: Modelling and simulation

During the 2017 Biennial meeting, the American Academy of Veterinary Pharmacology and Therapeutics hosted a 1-day session on the influence of population variability on dose-exposure-response relationships. In Part I, we highlighted some of the sources of population variability. Part II provides a summary of discussions on modelling and simulation tools that utilize existing pharmacokinetic data, can integrate drug physicochemical characteristics with species physiological characteristics and dosing information or that combine observed with predicted and in vitro information to explore and describe sources of variability that may influence the safe and effective use of veterinary pharmaceuticals.

In vitro nematicidal effect of Chenopodium ambrosioides and Castela tortuosa n-hexane extracts against Haemonchus contortus (Nematoda) and their anthelmintic effect in gerbils

The in vitro nematicidal effect of Chenopodium ambrosioides and Castela tortuosa n-hexane extracts (E-Cham and E-Cato, respectively) on Haemonchus contortus infective larvae (L3) and the anthelmintic effect of these extracts against the pre-adult stage of the parasite in gerbils were evaluated using both individual and combined extracts. The in vitro confrontation between larvae and extracts was performed in 24-well micro-titration plates. The results were considered 24 and 72 h post confrontation. The in vivo nematicidal effect was examined using gerbils as a study model. The extracts from the two assessed plants were obtained through maceration using n-hexane as an organic agent. Gerbils artificially infected with H. contortus L3 were treated intraperitoneally with the corresponding extract either individually or in combination. The results showed that the highest individual lethal in vitro effect (96.3%) was obtained with the E-Cham extract at 72 h post confrontation at 40 mg/ml, followed by E-Cato (78.9%) at 20 mg/ml after 72 h. The highest combined effect (98.7%) was obtained after 72 h at 40 mg/ml. The in vivo assay showed that the individual administration of the E-Cato and E-Cham extracts reduced the parasitic burden in gerbils by 27.1% and 45.8%, respectively. Furthermore, the anthelmintic efficacy increased to 57.3% when both extracts were administered in combination. The results of the present study show an important combined nematicidal effect of the two plant extracts assessed against L3 in gerbils.

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

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

Translating Pharmacokinetic and Pharmacodynamic Data into Practice

Pharmacokinetic (PK) and pharmacodynamic (PD) publications provide scientific evidence for incorporation in evidence-based veterinary medicine, aiding the clinician in selecting doses and dosing intervals. PK and PD studies have reported wide variations within exotic species, due to physiologic differences in absorption, distribution, metabolism, and excretion. PK studies offer species-specific data to help tailor doses and dosing routes to individual patients, minimize toxicity, and provide a cornerstone for PD studies to determine drug efficacy. This article reviews the application of PK parameters and the challenges in determining the PD activity of drugs, with a particular emphasis on exotic species.

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.

Integration of a plasma protein binding factor to the Chemical-Specific Adjustment Factor (CSAF) for facilitating the estimation of uncertainties in interspecies extrapolations when deriving health-based exposure limits for active pharmaceutical ingredients: Investigation of recent drug datasets

The objective was to challenge cross-species extrapolation factors with which to scale animal doses to human by any route for non-carcinogenic endpoints. The conventional hypothesis of the toxicokinetics (TK)-toxicodynamics (TD) relationship was equal toxicity at equal plasma level of the total drug moiety in each species, but this should also follow the free drug assumption, which states that only the unbound drug moiety in plasma may elicit a TD effect in tissue. Therefore, a protein binding factor (PBF) was combined with the Chemical-Specific Adjustment Factor (CSAF) (i.e., CSAF x PBF). The value of PBF of each drug was set equal to the ratio between human and animals of the unbound fraction in plasma (fu_p). Recent drug datasets were investigated. Our results indicate that any CSAF value would be increased or decreased while PBF deviates to the unity, and this required more attention. Accordingly, further testing indicated that the CSAF values set equal to basic allometric uncertainty factors according to the conventional hypothesis (dog∼2, monkey∼3.1, rat∼7, mouse∼12) would increase by including PBF for 30% of the drugs tested that showed a superior fu_p value in human compared to animals. However, default uncertainty factors in the range of 10-100 were less frequently exceeded. Overall, PBF could be combined with any other uncertainty factor to get reliable estimate of CSAF for each bound drug in deriving health-based exposure limits.

The 3Rs Concept: Time to Change How We Evaluate the Efficacy of Anthelmintics in Companion Animals

Experimental infections are required by current guidelines for investigating the efficacy of anthelmintics in dogs and cats. Recently, alternatives to experimental infections and the sacrificing of research dogs and cats have been evaluated, and novel conceptual investigations and methods of examination have been explored. Several of these approaches could potentially be used in efficacy studies for anthelmintics in dogs and cats. Here, we provide food for thought towards using new tools for evaluating the efficacy of anthelmintics in companion animals, for promoting the value of field trials, and for updating the existing guidelines for the efficacy testing of anthelmintics in dogs and cats.

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.

Pharmacokinetics of a single intramuscular injection of cefquinome in buffalo calves

The objective of this study was to investigate the pharmacokinetics of cefquinome following single intramuscular (IM) administration in six healthy male buffalo calves. Cefquinome was administered intramuscularly (2 mg/kg bodyweight) and blood samples were collected prior to drug administration and up to 24 hr after injection. No adverse effects or changes were observed after the IM injection of cefquinome. Plasma concentrations of cefquinome were determined by high-performance liquid chromatography. The disposition of plasma cefquinome is characterized by a mono-compartmental open model. The pharmacokinetic parameters after IM administration (mean ± SE) were C_max 6.93 ± 0.58 μg/ml, T_max 0.5 hr, t_½kα 0.16 ± 0.05 hr, t_½β 3.73 ± 0.10 hr, and AUC 28.40 ± 1.30 μg hr/ml after IM administration. A dosage regimen of 2 mg/kg bodyweight at 24-hr interval following IM injection of cefquinome would maintain the plasma levels required to be effective against the bacterial pathogens with MIC values ≤0.39 μg/ml. The suggested dosage regimen of cefquinome has to be validated in the disease models before recommending for clinical use in buffalo calves.

Pharmacokinetic and Pharmacodynamic Evaluation of Marbofloxacin and PK/PD Modeling against Escherichia coli in Pigs

The aim of this study was to evaluate the activity of marbofloxacin and establish the optimal dose regimens for decreasing the development of fluoroquinolone resistance in pigs against Escherichia coli with ex vivo pharmacokinetic/pharmacodynamic (PK/PD) modeling. The recommended dose (2 mg/kg body weight) of marbofloxacin was orally administered in healthy pigs. The ileum content and plasma were both collected for the determination of marbofloxacin. The main parameters of C_max, AUC_{0-24 h}, AUC, Ke, t_1/2ke, MRT and Cl_b were 11.28 μg/g, 46.15, 77.81 μg⋅h/g, 0.001 h^-1, 69.97 h, 52.45 h, 0.026 kg/h in ileum content, and 0.55 μg/ml, 8.15, 14.67 μg⋅h/ml, 0.023 h^-1, 30.67 h, 34.83 h, 0.14 L/h in plasma, respectively In total, 218 E. coli strains were isolated from most cities of China. The antibacterial activity in vitro and ex vivo of marbofloxacin against E. coli was determined following CLSI guidance. The MIC₉₀ of sensitive strains (142) was calculated as 2 μg/ml. The minimum inhibitory concentration (MIC) of HB197 was 2 and 4 μg/ml in broth and ileum fluids, respectively. In vitro mutant prevention concentration, growth and killing-time in vitro and ex vivo of marbofloxacin against selected HB197 were assayed for pharmacodynamic studies. According to the inhibitory sigmoid E_max modeling, the value of AUC_{0-24 h}/MIC produced in ileum content was achieved, and bacteriostatic, bactericidal activity, and elimination were calculated as 16.26, 23.54, and 27.18 h, respectively. Based on Monte Carlo simulations to obtain 90% target attainment rate, the optimal doses to achieve bacteriostatic, bactericidal, and elimination effects were 0.85, 1.22, and 1.41 mg/kg.bw for 50% target, respectively, and 0.92, 1.33, and 1.53 mg/kg.bw for 90% target, respectively, after oral administration. The results in this study provided a more optimized alternative for clinical use and demonstrated that the dosage 2 mg/kg of marbofloxacin by oral administration could have an effect on bactericidal activity against E. coli.

Higher bioavailability of doxycycline in broiler chickens with a novel in-feed pharmaceutical formulation

Bioavailability of a new, long-acting (LA) pharmaceutical preparation for administering doxycycline as in-feed medication to broiler chickens was compared to the standard in-feed administration of doxycycline. A commercial poultry house harboring Ross-308 broiler chickens, weighing 450 g, was divided into 7 sections as follows: doxy-FOLA group (n = 6,000 chickens divided into 3 replicates) medicated with 10% doxycyline, long-acting pellets at a dose of 400 g of doxycycline HCl/ton of food, resulting in a calculated dose of 48 mg/kg for 5 d; doxy-ref group (n = 6,000, divided into 3 replicates) medicated as for doxy-FOLA, but using a 20% commercial preparation of doxycycline. A third group of 300 broiler chickens (divided into 3 replicates), received a single IV dose of 48 mg/kg from a 2.4% solution of doxycycline HCl under ketamine anesthesia. Blood samples were obtained at designated times, serum was harvested, and doxycycline concentrations determined by high-performance liquid chromatography (HPLC). Bioavailability values were 156% and 227% on d 1 and 5 for doxy-FOLA and 13% and 23% for doxy-ref, on the same days. Mean residence time (MRT) and elimination half-life (T½β) were statistically different (P < 0.05) in doxy-FOLA group as compared to doxy-ref group (MRT: 26 h and 5.2 h; and T½β: 18 h vs 3 h, on the first day for doxy-FOLA and doxy-ref, respectively). Based on 3 levels of bacterial sensitivity of E. coli derived from a small survey carried out (i.e., 1.0, 2.0, and 4.0 μg/mL) and considering pharmacokinetic/pharmacodynamic (PK/PD) ratios required for this time-dependent antibacterial drug, it is possible to postulate that doxy-FOLA outstrips the reference preparation maintaining higher and more prolonged serum concentrations of doxycycline and consequently complying better with PK/PD ratios regarded as optimal for this drug. The advantages of using doxy-FOLA in poultry medicine include a more comprehensive use of the active principle, which in turn should have a better impact on bacterial diseases. Yet, a longer withdrawal time is anticipated based on an almost 4-fold increment in the MRT value.

Pharmacokinetics, bioavailability and dose assessment of Cefquinome against Escherichia coli in black swans (Cygnus atratus)

BACKGROUND

The objective of this study is to investigate pharmacokinetics and dose regimens of cefquinome in black swans following intravenous (IV) and intramuscular (IM) administration at a single dose of 2 mg/kg. The MICs of cefquinome against 49 Escherichia coli isolates from black swans were determined. Monte Carlo simulation was applied to conduct the dose regimen assessment and optimization of cefquinome against E. coli in black swans, and a pharmacokinetic/pharmacodynamic (PK/PD) cutoff was established for E. coli isolates obtained in this study.

RESULTS

The PK parameters of T_1/2α (0.31 h), T_1/2β (1.69 h) and Cl_B (0.13 L/kg·h) indicated a rapid distribution and elimination of cefquinome in black swans after IV administration. After IM injection, the corresponding PK parameters of T_1/2Ka, T_1/2Ke, T_max, C_max, and F were 0.12 h, 1.62 h, 0.39 h, 5.71 μg/mL and 74.2%, respectively. The MICs of cefquinome against black swans E. coli ranged from 0.03 to 8 μg/mL, with MIC₅₀ and MIC₉₀ of 0.06 and 0.5 μg/mL, respectively. The PK/PD cutoff of cefquinome against E. coli was determined to be 0.2 μg/mL. Monte Carlo simulation showed that the nominal dose regimen (2 mg/kg/24 h) could not achieve a satisfactory probability of target attainment (PTA) for %T_MIC ≥ 50%, indicating a risk of treatment failure and the development of potential drug resistance.

CONCLUSIONS

The current daily dosage of cefquinome when divided into 12-h interval (1 mg/kg/12 h) may be effective for the treatment of E. coli infections with an MIC ≤0.5 μg/mL.