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

Pharmacokinetic/pharmacodynamic integration of tilmicosin against Pasteurella multocida in a piglet tissue cage model

Tilmicosin is a semi-synthetic macrolide for veterinary use with strong antibacterial effect on respiratory bacteria. In this study, the pharmacokinetic/pharmacodynamic (PK/PD) integration of tilmicosin against Pasteurella multocida (P. multocida) was evaluated by establishing a piglet tissue cage infection model. Concentration of tilmicosin and bacterial numbers of P. multocida in the tissue-cage fluid were monitered. After the population of P. multocida was equal to or greater than 107 CFU/mL in a tissue cage, piglets received an oral administration of tilmicosin at a dose of 30, 40, 50, and 60 mg/kg b.w., once daily for 3 days, respectively. Bacteria were counted every 24 h after drug administration and at 48 and 72 h after the last administration. A sigmoidal Emax model was used to fit the relationship between PK/PD parameters and the antibacterial effect. AUC24h/MIC was the best PK/PD index that correlated with effectiveness of tilmicosin against P. multocida. The magnitude of AUC24h/MIC required for continuous 1/3-log, 1/2-log, and 3/4-log reductions were 19.65 h, 23.86 h, and 35.77 h, respectively, during each 24 h treatment period. In this study, when the dosage was >50 mg/kg, the AUC24h/MIC was still >35.77 h in the period of 24-48 h after the last administration due to the slow elimination, that is, tilmicosin exhibited a potent antibacterial effect against P. multocida after three successive daily administrations. The data provide meaningful guidance to optimize regimens of tilmicosin to treat respiratory tract infections caused by P. multocida.

Population pharmacokinetics and pharmacokinetic/pharmacodynamic evaluation of marbofloxacin against Coagulase-negative staphylococci, Staphylococcus aureus and Mycoplasma agalactiae pathogens in goats

Marbofloxacin is a broad-spectrum fluoroquinolone, and an extra-label use has been reported in horse, sheep and goat. However, extrapolation of dosage regimens from cattle to horse and small ruminants could lead to incorrect dosing due to pharmacokinetic differences among species, increasing the risk of antimicrobial resistance or toxicity. Pharmacokinetic properties of marbofloxacin, including PK/PD analysis, have been studied by intravenous, intramuscular and subcutaneous administration in lactating and non-lactating goats. A population pharmacokinetic model of marbofloxacin in goats was built using 10 pharmacokinetic studies after intravenous, intramuscular, and subcutaneous administration at a dose of 2, 5 and 10 mg/kg. Serum or plasma and milk concentration-time profiles were simultaneously fitted with a non-linear mixed effect model with Monolix software. Level of milk production (lactating and non-lactating) and health status (healthy and un-healthy) were retained as covariates on volume of distribution and clearance. Marbofloxacin concentrations were well described in plasma/serum and milk by the population model. Simulated dose regimens of marbofloxacin administered at 2, 5 and 10 mg/kg by intramuscular route for five days were evaluated (n = 5000 per group). Steady-state fAUCs for each dose regimen were obtained. Probability of target attainment of fAUC/MIC ratios were determined and PK/PDco values (highest MIC for which 90% of individuals can achieve a prior numerical value of the fAUC/MIC index) were established using Monte Carlo simulations (n = 50,000). MIC values for wild type isolates of Staphylococcus aureus, coagulase negative staphylococci, and Mycoplasma agalactiae were determined and tentative epidemiological cutoff (TECOFF) were obtained at 1.0, 0.5 and 0.5 mg/L, respectively. The PK/PDco for the dose regimen of 2 mg/kg/24 h and 5 mg/kg/24 h (0.125 and 0.25 mg/L) were lower than TECOFF (0.5 and 1 mg/L). The dosage regimen of 10 mg/kg/24 h was adequate for intermediate MIC values of 0.125-0.50 mg/L and could be effective for a population with a target fAUC/MIC ratio ˂ 48 for Coagulase negative staphylococci and Mycoplasma agalactiae, but not for Staphylococcus aureus. Results obtained in this study could be taken as a starting point by committees that set the clinical breakpoints and justifies expert rules to optimize marbofloxacin dose regimens.

PK/PD Analysis by Nonlinear Mixed-Effects Modeling of a Marbofloxacin Dose Regimen for Treatment of Goat Mastitis Produced by Coagulase-Negative Staphylococci

Simple Summary

Coagulase-negative staphylococci are main pathogens that produce goat mastitis. Marbofloxacin is a third-generation fluoroquinolone approved to treat mastitis in animals. Since the efficacy of an antimicrobial is related with its concentration in the site of infection, and the latter depends of dose and biological processes that determine the distribution of the antimicrobial in different tissues and secretions, the objectives of this study were to evaluate the efficacy of a dose regimen of marbofloxacin (10 mg/kg/24 h) administered intramuscularly for five days in goats with mastitis induced by coagulase-negative staphylococci, by an evaluation of the concentrations of marbofloxacin achieved in blood and milk over time (called pharmacokinetics), and characterizing the concentration–effect relationship of marbofloxacin against coagulase-negative staphylococci in Mueller Hinton broth and goat milk, by time kill assays, in order to determine the concentrations of marbofloxacin related with an adequate bacterial count reduction (measured by efficacy index AUC/MIC). The proposed dose regimen was adequate for the treatment of goat mastitis produced by coagulase-negative staphylococci, resulting in a microbiological and clinical cure of all animals. The animal model used in this study provided important pharmacokinetic information about the effect of the infection on the pharmacokinetics of marbofloxacin. Pharmacodynamic modeling showed that marbofloxacin concentrations needed for antimicrobial efficacy were higher in goat milk compared with Mueller Hinton broth. Bacterial resistance to antimicrobials is a serious problem, since marbofloxacin is considered a critically important antimicrobial, and its rational and prudent use could extend its utility over time.

Abstract

Coagulase-negative staphylococci are main pathogens that produce goat mastitis. Marbofloxacin is a third-generation fluoroquinolone approved for treat mastitis in animals. The objectives of this study were: (i) to determine the pharmacokinetics of marbofloxacin (10 mg/kg/24 h) in serum and milk administered intramuscularly for five days in goats with mastitis induced by coagulase-negative staphylococci; (ii) to characterize the concentration–effect relationship of marbofloxacin against coagulase-negative staphylococci in Mueller Hinton broth and goat milk; (iii) to determine AUC/MIC cutoff values of marbofloxacin, and (iv) to perform a PK/PD analysis to evaluate the efficacy of the dose regimen for the treatment of goat mastitis produced by coagulase-negative staphylococci. Marbofloxacin presented context-sensitive pharmacokinetics, influenced by the evolution of the disease, which decreased marbofloxacin disposition in serum and milk. Marbofloxacin showed a median (95% CI) fAUC/MIC values for MIC of 0.4 and 0.8 µg/mL of 26.66 (22.26–36.64) and 32.28 (26.57–48.35) related with −2 log₁₀CFU/mL reduction; and 32.26 (24.81–81.50) and 41.39 (29.38–128.01) for −3 log₁₀CFU/mL reduction in Mueller Hinton broth. For milk, −2 log₁₀CFU/mL reduction was achieved with 41.48 (35.29–58.73) and 51.91 (39.09–131.63), and −3 log₁₀CFU/mL reduction with 51.04 (41.6–82.1) and 65.65 (46.68–210.16). The proposed dose regimen was adequate for the treatment of goat mastitis produced by coagulase-negative staphylococci, resulting in microbiological and clinical cure of all animals. The animal model used in this study provided important pharmacokinetic information about the effect of the infection on the pharmacokinetics of marbofloxacin. Pharmacodynamic modeling showed that fAUC/MIC cutoff values were higher in goat milk compared with Mueller Hinton broth.

PK/PD Analysis of Marbofloxacin by Monte Carlo Simulation against Mycoplasmaagalactiae in Plasma and Milk of Lactating Goats after IV, SC and SC-Long Acting Formulations Administration

Simple Summary

In some countries like Spain and France, contagious agalactia (CA) is a highly relevant issue. CA is a mycoplasmosis affecting small ruminants and it is associated with a relevant economic impact on dairy. The poor efficacy of vaccines and their inability to prevent disease transmission is conducive to the use of antibiotics to control CA. However, only a few groups of antimicrobial agents are effective against these species, and selecting an adequate antimicrobial agent following the categorization of antibiotics made by the different international organisms (European Medicine Agency, World Health Organization) in veterinary medicine becomes a difficult task. The PK/PD approach is a useful tool to guide veterinarians on the appropriate targets through a rational selection of the best dose regimen of antimicrobial agents. In this study, marbofloxacin pharmacokinetics was studied after three routes of administration with two long-acting formulations. The minimum inhibitory concentrations (MIC) values of Mycoplasma agalactia isolated from goats affected by CA in Spain were calculated. The results show that systemic exposure achieved in lactating goats following these formulations provides rate of drug release that could be adequate to maintain effective plasma concentrations against M. agalactiae. The PK/PD analysis by Monte Carlo simulation showed that a dosage regimen from 8.47 to 11.57 mg/kg every 24 h could effectively treat goats affected by CA.

Abstract

Contagious agalactia is a mycoplasmosis affecting small ruminants that have become an important issue in many countries. However, PK/PD studies of antibiotics to treat this problem in lactating goats affected by Mycoplasma (M.) agalactiae, the main CA-causing mycoplasma are almost non-existent. The aims of this study were to evaluate the plasma and milk disposition of marbofloxacin in lactating goats after intravenous (IV), subcutaneous (SC) and subcutaneous poloxamer P407 formulations with and without carboxy-methylcellulose (SC-P407-CMC and SC-P407) administration. Marbofloxacin concentrations were analysed by the High Performance Liquid Chromatography (HPLC) method. Minimum inhibitory concentrations (MIC) of M. agalactiae field isolates from mastitic goat’s milk were used to calculate surrogate markers of efficacy. Terminal half-lives of marbofloxacin after IV, SC, SC-P407 and SC-P407-CMC administration were 7.12, 6.57, 13.92 and 12.19 h in plasma, and the half-lives of elimination of marbofloxacin in milk were 7.22, 7.16, 9.30 and 7.74 h after IV, SC, SC-P407 and SC-P407-CMC administration, respectively. Marbofloxacin penetration from the blood into the milk was extensive, with Area Under the Curve (AUC_milk/AUC_plasma) ratios ranged 1.04–1.23, and maximum concentrations (C_max-milk/C_max-plasma) ratios ranged 0.72–1.20. The PK/PD surrogate markers of efficacy fAUC24/MIC and the Monte Carlo simulation show that marbofloxacin ratio (fAUC₂₄/MIC > 125) using a 90% of target attainment rate (TAR) need a dose regimen between 8.4 mg/kg (SC) and 11.57 mg/kg (P407CMC) and should be adequate to treat contagious agalactia in lactating goats.

Evaluation of the pharmacokinetic-pharmacodynamic integration of marbofloxacin in combination with methyl gallate against Salmonella Typhimurium in rats

Fluoroquinolone resistance in Salmonella Typhimurium is becoming a major concern. Hence, an intervention to limit the growth in resistance is inevitable. One way to combat this challenge is through combination therapy. The combination of antibiotics with phytochemicals has become an ideal means of preventing antimicrobial resistance. Recently, in an in vitro study, the combination of methyl gallate (MG) with marbofloxacin (MAR) has shown to prevent Salmonella Typhimurium invasion. It is also worth to study the effects of plant extracts on the pharmacokinetics of antibiotics. Hence, the objective of this study was to determine the effect of MG on the pharmacokinetics of MAR and pharmacokinetics/pharmacodynamics integration of MG and MAR. The micro-broth dilution method was used to obtain the minimum inhibitory concentration (MIC), and fractional inhibitory concentration (FIC) of MAR and MG. Whereas, the pharmacokinetic was conducted in rats by administering either MAR alone or combined with MG through oral and/or intravenous routes. The results indicated that the MIC of MAR and MG against standard strain Salmonella Typhimurium (ATCC 14028) was 0.031 and 500 μg/mL, respectively. The FIC_index of the combination of MAR and MG was 0.5. For orally administered drugs, the C_max and AUC_24h of MAR were 1.04 and 0.78 μg/mL and 5.98 and 6.11 h.μg/mL when MAR was given alone and in combination with MG, respectively. The intravenous administration of MAR showed a half-life of 3.8 and 3.9 h; a clearance rate of 1.1 and 0.73 L/h/kg and a volume of distribution of 5.98 and 4.13 L/kg for MAR alone and in combination with MG, respectively. The AUC₂₄/MIC for MAR alone and in combination with MG was 192.8 and 381.9 h, respectively. In conclusion, MG has shown to increase the antimicrobial activity of MAR in vitro and ex vivo experiments without affecting the pharmacokinetics of MAR in rats.

Tolfenamic acid on-line preconcentration strategy on carbon nanotubes minicolumn with fluorimetric detection

Nonsteroidal anti-inflammatory agents (NSAIDs) are a group of pharmaceuticals considered one of the most popular drugs used in clinical practice applied to the treatment of acute and chronic conditions. Some pharmaceuticals products are excreted reaching the environment and altering the balance of ecosystems. This work proposes a new fluorimetric flow injection (FI) methodology for the NSAID tolfenamic acid quantification based on the quenching effect of the analyte on fluorescent signal of bovine serum albumin fluorophore. Results put in evidence a mechanism of static quenching, with a Stern Volmer constant value of 1.8 × 10⁷ L mol^-1. To achieve the selective on-line preconcentration of analyte, a carbon nanotubes mini column was introduced in the FI configuration producing a beneficial effect on high sampling frequency, minimum sample and reagents consumption. The experimental factors that influence batch fluorescent signal and FI analysis have been studied and optimized. At optimal experimental conditions, an adequate tolerance to foreign species was shown. With the flow configuration, a LOD of 0.019 μg L^-1, a LOQ of 0.058 μg L^-1 were obtained with a sampling rate of 30 samples h^-1. The new methodology was successfully applied to analyte determination in tap water and pharmaceutical and factory waste samples with recuperation near to 100%.

Pharmacokinetics of marbofloxacin in Green sea turtles (Chelonia mydas) following intravenous and intramuscular administration at two dosage rates

Limited pharmacokinetic information to establish suitable therapeutic plans is available for green sea turtles. Therefore, the present study was conducted to evaluate the pharmacokinetic characteristics of marbofloxacin (MBF) in the green sea turtle, Chelonia mydas, following single intravenous (i.v.) or intramuscular (i.m.) administration at two dosages of 2 and 4 mg/kg body weight (b.w.). Blood samples were collected at assigned times up to 168 hr. MBF in plasma was extracted using liquid-liquid extraction and analyzed by a validated high-performance liquid chromatography (HPLC). MBF was quantifiable from 15 min to 96 hr after i.v. and i.m. administrations at two dose rates. A noncompartmental model was used to fit the plasma concentration of MBF versus time curve for each green sea turtle. The t_1/2λz value, similar for both the dosages (22-28 hr), indicated that the overall rate of elimination of MBF in green sea turtles is relatively slow. The average i.m. F% ranged 88%-103%. MBF is a concentration-dependent drug and the AUC/MIC ratio is the best PK/PD predictor for its efficacy. The MBF dosage of 4 mg/kg appeared to produce an appropriate value of the PK-PD surrogate that predicts antibacterial success for disease caused by susceptible bacteria. In contrast, i.m. administration of MBF at a dosage of 2 mg/kg b.w. was not found to produce a suitable PK-PD surrogate index. However, further studies of multiple doses and plasma binding proteins are warranted to confirm an appropriate dosage regimen.

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.

Effects of TNFR1 gene silencing on early apoptosis of marbofloxacin-treated chondrocytes from juvenile dogs

Quinolones (QNs)-induced cartilaginous lesions in juvenile animals by chondrocyte apoptosis is an important toxic effect, which results in the restriction of their use in pediatrics. However, limited data about QNs chondrotoxicity are available for evaluation of the potential toxicity in both animals and human cartilage. To explore whether tumor necrosis factor/its receptor (TNF/TNFR1) signaling pathway is involved in the early apoptosis of marbofloxacin-induced chondrocytes, canine juvenile chondrocytes were treated with 0, 20, 50 and 100 μg/mL marbofloxacin. Results showed that the apoptosis rates of the chondrocytes at 2, 8 and 24 h were significantly increased in a concentration- and time-dependent manner (P <  0.05). The mRNA levels of apoptosis-related factors in TNF/TNFR1 signaling pathways and the protein levels of TNFα and TNFR1 were increased in canine chondrocytes treated with 20-100 μg/mL marbofloxacin (P <  0.05) while TNFR1 gene silencing significantly decreased the chondrocyte apoptosis and inhibited the mRNA expression of TNF/TNFR1 downstream signaling molecules after 100 μg/mL marbofloxacin treatment at 8 h (P <  0.01). It was confirmed that activated TNF/TNFR1 signaling pathway may play a leading role in the early apoptosis of marbofloxacin-induced canine juvenile chondrocytes, which is helpful for clinical estimation or prevention of the risk of QNs.

Molecular mechanism of action responsible for carrageenan-induced inflammatory response

Carrageenan-induced inflammation has long been used as an in vivo model of local inflammation. We developed an in vitro model of inflammation using primary blood cells to characterize gene induction following carrageenan (λ-CGN) stimulation and identify the signal transduction pathway(s) through which λ-CGN worked, using swine whole blood cultures from Yorkshire barrows. Blood samples were divided into stimulated and unstimulated groups. Unstimulated blood was a control for λ-CGN treated cultures to delineate treatment effects from time-in-culture effects. All cultures were collected and separated into two fractions; supernatant for ELISA analyses and white blood cells for mRNA expression. Lambda (λ)-CGN induced MCP-1 at the proteomic and the genomic levels. Lambda-CGN increased IL-8 protein production but had no impact on serum amyloid A protein levels. Alveolar Macrophage-Derived Neutrophil Chemotactic Factor-II (AMCF-II), a swine-specific member of the IL8/GRO family, showed increased gene expression. TNF-α and IL-6 protein levels were not induced by λ-CGN stimulation. Stimulation of HEK-293 cells co-transfected with a single pattern recognition receptor and the secreted embryonic alkaline phosphatase (SEAP) read-out system demonstrated that λ-CGN signals through the TLR-2 and TLR-4 signal transduction pathways. Using silencing RNA to inhibit TLR6 expression in TLR2 transfected HEK-293 cells indicated that λ-CGN works through the TLR2/6 pathway. Silencing TLR6 expression in TLR4 transfected HEK-293 cells showed that λ-CGN stimulation of this cell line worked through a TLR4/6 heterodimer, as lipopolysaccharide (LPS) induced SEAP production through a TLR4 homodimer. These results demonstrate that although carrageenan can stimulate through TLR4 signaling pathways, it initiates an inflammatory response in these cells that differs from a typical endotoxin effect such as LPS stimulation, in terms of the pathways and gene products altered, suggesting that activation of TLR2/6 and TLR4/6 are the predominant pathways through which carrageenan induces inflammatory responses.

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.

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

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

Tolfenamic Acid

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

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

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

What is the true in vitro potency of oxytetracycline for the pig pneumonia pathogens Actinobacillus pleuropneumoniae and Pasteurella multocida?

The pharmacodynamics of oxytetracycline was determined for pig respiratory tract pathogens, Actinobacillus pleuropneumoniae and Pasteurella multocida. Indices of potency were determined for the following: (i) two matrices, broth and pig serum; (ii) five overlapping sets of twofold dilutions; and (iii) a high strength starting culture. For A. pleuropneumoniae, minimum inhibitory concentration (MIC) was similar for the two matrices, but for P. multocida, differences were marked and significantly different. MIC and minimum bactericidal concentration (MBC) serum: broth ratios for A. pleuropneumoniae were 0.83:1 and 1.22:1, respectively, and corresponding values for P. multocida were 22.0:1 and 7.34:1. For mutant prevention concentration (MPC) serum: broth ratios were 0.79:1 (A. pleuropneumoniae) and 20.9:1 (P. multocida). These ratios were corrected for serum protein binding to yield fraction unbound (fu) serum: broth MIC ratios of 0.24:1 (A. pleuropneumoniae) and 6.30:1 (P. multocida). Corresponding fu serum: broth ratios for MPC were almost identical, 0.23:1 and 6.08:1. These corrections for protein binding did not account for potency differences between serum and broth for either species; based on fu serum MICs, potency in serum was approximately fourfold greater than predicted for A. pleuropneumoniae and sixfold smaller than predicted for P. multocida. For both broth and serum and both bacterial species, MICs were also dependent on initial inoculum strength. The killing action of oxytetracycline had the characteristics of codependency for both A. pleuropneumoniae and P. multocida in both growth media. The in vitro potency of oxytetracycline in pig serum is likely to be closer to the in vivo plasma/serum concentration required for efficacy than potency estimated in broths.

Pharmacokinetic-pharmacodynamic integration and modelling of oxytetracycline for the calf pathogens Mannheimia haemolytica and Pasteurella multocida

A calf tissue cage model was used to study the pharmacokinetics (PK) and pharmacodynamics (PD) of oxytetracycline in serum, inflamed (exudate) and noninflamed (transudate) tissue cage fluids. After intramuscular administration, the PK was characterized by a long mean residence time of 28.3 hr. Based on minimum inhibitory concentrations (MICs) for six isolates each of Mannheimia haemolytica and Pasteurella multocida, measured in serum, integration of in vivo PK and in vitro PD data established area under serum concentration-time curve (AUC_0-∞ )/MIC ratios of 30.0 and 24.3 hr for M. haemolytica and P. multocida, respectively. Corresponding AUC_0-∞ /MIC ratios based on MICs in broth were 656 and 745 hr, respectively. PK-PD modelling of in vitro bacterial time-kill curves for oxytetracycline in serum established mean AUC_0-24 hr /MIC ratios for 3log₁₀ decrease in bacterial count of 27.5 hr (M. haemolytica) and 60.9 hr (P. multocida). Monte Carlo simulations predicted target attainment rate (TAR) dosages. Based on the potency of oxytetracycline in serum, the predicted 50% TAR single doses required to achieve a bacteriostatic action covering 48-hr periods were 197 mg/kg (M. haemolytica) and 314 mg/kg (P. multocida), respectively, against susceptible populations. Dosages based on the potency of oxytetracycline in broth were 25- and 27-fold lower (7.8 and 11.5 mg/kg) for M. haemolytica and P. multocida, respectively.

Prediction of marbofloxacin dosage for the pig pneumonia pathogens Actinobacillus pleuropneumoniae and Pasteurella multocida by pharmacokinetic/pharmacodynamic modelling

Background

Bacterial pneumonia in pigs occurs widely and requires antimicrobial therapy. It is commonly caused by the pathogens Actinobacillus pleuropneumoniae and Pasteurella multocida. Marbofloxacin is an antimicrobial drug of the fluoroquinolone class, licensed for use against these organisms in the pig. In recent years there have been major developments in dosage schedule design, based on integration and modelling of pharmacokinetic (PK) and pharmacodynamic (PD) data, with the objective of optimising efficacy and minimising the emergence of resistance. From in vitro time-kill curves in pig serum, PK/PD breakpoint Area under the curve (AUC) _24h /minimum inhibitory concentration (MIC) values were determined and used in conjunction with published PK, serum protein binding data and MIC distributions to predict dosages based on Monte Carlo simulation (MCS).

Results

For three levels of inhibition of growth, bacteriostasis and 3 and 4log₁₀ reductions in bacterial count, mean AUC_24h/MIC values were 20.9, 45.2 and 71.7 h, respectively, for P. multocida and 32.4, 48.7 and 55.5 h for A. pleuropneumoniae. Based on these breakpoint values, doses for each pathogen were predicted for several clinical scenarios: (1) bacteriostatic and bactericidal levels of kill; (2) 50 and 90% target attainment rates (TAR); and (3) single dosing and daily dosing at steady state. MCS for 90% TAR predicted single doses to achieve bacteriostatic and bactericidal actions over 48 h of 0.44 and 0.95 mg/kg (P. multocida) and 0.28 and 0.66 mg/kg (A. pleuropneumoniae). For daily doses at steady state, and 90% TAR bacteriostatic and bactericidal actions, dosages of 0.28 and 0.59 mg/kg (P. multocida) and 0.22 and 0.39 mg/kg (A. pleuropneumoniae) were required for pigs aged 12 weeks. Doses were also predicted for pigs aged 16 and 27 weeks.

Conclusions

PK/PD modelling with MCS approaches to dose determination demonstrates the possibility of tailoring clinical dose rates to a range of bacterial kill end-points.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-017-1128-y) contains supplementary material, which is available to authorized users.

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

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

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.

Pharmacokinetics, milk penetration and PK/PD analysis by Monte Carlo simulation of marbofloxacin, after intravenous and intramuscular administration to lactating goats

The main objectives of this study were (i) to evaluate the serum pharmacokinetic behaviour and milk penetration of marbofloxacin (MFX; 5 mg/kg), after intravenous (IV) and intramuscular (IM) administration in lactating goats and simulate a multidose regimen on steady-state conditions, (ii) to determine the minimum inhibitory concentration (MIC) and mutant prevention concentration (MPC) of coagulase negative staphylococci (CNS) isolated from caprine mastitis in Córdoba, Argentina and (iii) to make a PK/PD analysis by Monte Carlo simulation from steady-state pharmacokinetic parameters of MFX by IV and IM routes to evaluate the efficacy and risk of the emergence of resistance. The study was carried out with six healthy, female, adult Anglo Nubian lactating goats. Marbofloxacin was administered at 5 mg/kg bw by IV and IM route. Serum and milk concentrations of MFX were determined with HPLC/uv. From 106 regional strains of CNS isolated from caprine mastitis in herds from Córdoba, Argentina, MICs and MPCs were determined. MIC₉₀ and MPC₉₀ were 0.4 and 6.4 μg/ml, respectively. MIC and MPC-based PK/PD analysis by Monte Carlo simulation indicates that IV and IM administration of MFX in lactating goats may not be adequate to recommend it as an empirical therapy against CNS, because the most exigent endpoints were not reached. Moreover, this dose regimen could increase the probability of selecting mutants and resulting in emergence of resistance. Based on the results of Monte Carlo simulation, the optimal dose of MFX to achieve an adequate antimicrobial efficacy should be 10 mg/kg, but it is important take into account that fluoroquinolones are substrates of efflux pumps, and this fact may determine that assumption of linear pharmacokinetics at high doses of MFX may be incorrect.

Factors influencing the potency of marbofloxacin for pig pneumonia pathogens Actinobacillus pleuropneumoniae and Pasteurella multocida

For the pig respiratory tract pathogens, Actinobacillus pleuropneumoniae and Pasteurella multocida, Minimum Inhibitory Concentration (MIC) of marbofloxacin was determined in recommended broths and pig serum at three inoculum strengths. MICs in both growth matrices increased progressively from low, through medium to high starting inoculum counts, 10⁴, 10⁶ and 10⁸CFU/mL, respectively. P. multocida MIC ratios for high:low inocula were 14:4:1 for broth and 28.2:1 for serum. Corresponding MIC ratios for A. pleuropneumoniae were lower, 4.1:1 (broth) and 9.2:1 (serum). MIC high:low ratios were therefore both growth matrix and bacterial species dependent. The effect of alterations to the chemical composition of broths and serum on MIC were also investigated. Neither adjusting broth or serum pH in six increments over the range 7.0 to 8.0 nor increasing calcium and magnesium concentrations of broth in seven incremental steps significantly affected MICs for either organism. In time-kill studies, the killing action of marbofloxacin had the characteristics of concentration dependency against both organisms in both growth matrices. It is concluded that MIC and time-kill data for marbofloxacin, generated in serum, might be preferable to broth data, for predicting dosages of marbofloxacin for clinical use.

Pharmacokinetic/pharmacodynamic integration and modelling of oxytetracycline for the porcine pneumonia pathogens Actinobacillus pleuropneumoniae and Pasteurella multocida

Pharmacokinetic–pharmacodynamic (PK/PD) integration and modelling were used to predict dosage schedules of oxytetracycline for two pig pneumonia pathogens, Actinobacillus pleuropneumoniae and Pasteurella multocida. Minimum inhibitory concentration (MIC) and mutant prevention concentration (MPC) were determined in broth and porcine serum. PK/PD integration established ratios of average concentration over 48 h (C_av0–48 h)/MIC of 5.87 and 0.27 μg/mL (P. multocida) and 0.70 and 0.85 μg/mL (A. pleuropneumoniae) for broth and serum MICs, respectively. PK/PD modelling of in vitro time–kill curves established broth and serum breakpoint values for area under curve (AUC_0–24 h)/MIC for three levels of inhibition of growth, bacteriostasis and 3 and 4 log₁₀ reductions in bacterial count. Doses were then predicted for each pathogen, based on Monte Carlo simulations, for: (i) bacteriostatic and bactericidal levels of kill; (ii) 50% and 90% target attainment rates (TAR); and (iii) single dosing and daily dosing at steady‐state. For 90% TAR, predicted daily doses at steady‐state for bactericidal actions were 1123 mg/kg (P. multocida) and 43 mg/kg (A. pleuropneumoniae) based on serum MICs. Lower TARs were predicted from broth MIC data; corresponding dose estimates were 95 mg/kg (P. multocida) and 34 mg/kg (A. pleuropneumoniae).

Potency of marbofloxacin for pig pneumonia pathogens Actinobacillus pleuropneumoniae and Pasteurella multocida: Comparison of growth media

Pharmacodynamic properties of marbofloxacin were established for six isolates each of the pig respiratory tract pathogens, Actinobacillus pleuropneumoniae and Pasteurella multocida. Three in vitro indices of potency were determined; Minimum Inhibitory Concentration (MIC), Minimum Bactericidal Concentration (MBC) and Mutant Prevention Concentration (MPC). For MIC determination Clinical Laboratory Standards Institute guidelines were modified in three respects: (1) comparison was made between two growth media, an artificial broth and pig serum; (2) a high inoculum count was used to simulate heavy clinical bacteriological loads; and (3) five overlapping sets of two-fold dilutions were used to improve accuracy of determinations. Similar methods were used for MBC and MPC estimations. MIC and MPC serum:broth ratios for A. pleuropneumoniae were 0.79:1 and 0.99:1, respectively, and corresponding values for P. multocida were 1.12:1 and 1.32:1. Serum protein binding of marbofloxacin was 49%, so that fraction unbound (fu) serum MIC values were significantly lower than those predicted by correction for protein binding; fu serum:broth MIC ratios were 0.40:1 (A. pleuropneumoniae) and 0.50:1 (P. multocida). For broth, MPC:MIC ratios were 13.7:1 (A. pleuropneumoniae) and 14.2:1 (P. multocida). Corresponding ratios for serum were similar, 17.2:1 and 18.8:1, respectively. It is suggested that, for dose prediction purposes, serum data might be preferable to potency indices measured in broths.

Comparison of standardised versus non-standardised methods for testing the in vitro potency of oxytetracycline against Mannheimia haemolytica and Pasteurella multocida

The in vitro pharmacodynamics of oxytetracycline was established for six isolates of each of the calf pneumonia pathogens Mannheimia haemolytica and Pasteurella multocida. Minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and bacterial time-kill curves were determined in two matrices, Mueller Hinton broth (MHB) and calf serum. Geometric mean MIC ratios, serum:MHB, were 25.2:1 (M. haemolytica) and 27.4:1 (P. multocida). The degree of binding of oxytetracycline to serum protein was 52.4%. Differences between serum and broth MICs could not be accounted for by oxytetracycline binding to serum protein. In vitro time-kill data suggested a co-dependent killing action of oxytetracycline. The in vitro data indicate inhibition of the killing action of oxytetracycline by serum factor(s). The nature of the inhibition requires further study. The outcome of treatment with oxytetracycline of respiratory tract infections in calves caused by M. haemolytica and P. multocida may not be related solely to a direct killing action.

Application of PK/PD Modeling in Veterinary Field: Dose Optimization and Drug Resistance Prediction

Among veterinary drugs, antibiotics are frequently used. The true mean of antibiotic treatment is to administer dose of drug that will have enough high possibility of attaining the preferred curative effect, with adequately low chance of concentration associated toxicity. Rising of antibacterial resistance and lack of novel antibiotic is a global crisis; therefore there is an urgent need to overcome this problem. Inappropriate antibiotic selection, group treatment, and suboptimal dosing are mostly responsible for the mentioned problem. One approach to minimizing the antibacterial resistance is to optimize the dosage regimen. PK/PD model is important realm to be used for that purpose from several years. PK/PD model describes the relationship between drug potency, microorganism exposed to drug, and the effect observed. Proper use of the most modern PK/PD modeling approaches in veterinary medicine can optimize the dosage for patient, which in turn reduce toxicity and reduce the emergence of resistance. The aim of this review is to look at the existing state and application of PK/PD in veterinary medicine based on in vitro, in vivo, healthy, and disease model.

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

BACKGROUND

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

RESULTS

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

CONCLUSIONS

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

Pharmacokinetic/pharmacodynamic integration and modelling of amoxicillin for the calf pathogens Mannheimia haemolytica and Pasteurella multocida

The antimicrobial properties of amoxicillin were determined for the bovine respiratory tract pathogens, Mannheima haemolytica and Pasteurella multocida. Minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and time-kill curves were established. Pharmacokinetic (PK)/pharmacodynamic (PD) modelling of the time-kill data, based on the sigmoidal Emax equation, generated parameters for three levels of efficacy, namely bacteriostatic, bactericidal (3log10 reduction) and 4log10 reduction in bacterial counts. For these levels, mean AUC(0-24 h) /MIC serum values for M. haemolytica were 29.1, 57.3 and 71.5 h, respectively, and corresponding values for P. multocida were 28.1, 44.9 and 59.5 h. Amoxicillin PK was determined in calf serum, inflamed (exudate) and noninflamed (transudate) tissue cage fluids, after intramuscular administration of a depot formulation at a dosage of 15 mg/kg. Mean residence times were 16.5 (serum), 29.6 (exudate) and 29.0 h (transudate). Based on serum MICs, integration of in vivo PK and in vitro PD data established maximum concentration (Cmax )/MIC ratios of 13.9:1 and 25.2:1, area under concentration-time curve (AUC0-∞ )/MIC ratios of 179 and 325 h and T>MIC of 40.3 and 57.6 h for P. multocida and M. haemolytica, respectively. Monte Carlo simulations for a 90% target attainment rate predicted single dose to achieve bacteriostatic and bactericidal actions over 48 h of 17.7 and 28.3 mg/kg (M. haemolytica) and 17.7 and 34.9 mg/kg (P. multocida).

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

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

Pharmacokinetic and pharmacodynamic integration and modelling of marbofloxacin in calves for Mannheimia haemolytica and Pasteurella multocida

The pharmacokinetics (PK) and pharmacodynamics (PD) of marbofloxacin were established in calves for six strains of each of the pneumonia pathogens Mannheimia haemolytica and Pasteurella multocida. The distribution of marbofloxacin into inflamed (exudate) and non-inflamed (transudate) tissue cage fluids allowed comparison with the serum concentration-time profile. To establish the PD profile, minimum inhibitory concentration (MIC) was determined in Mueller-Hinton broth (MHB) and calf serum. Moderately higher MICs were obtained for serum compared to MHB. An initial integration of PK-PD data established C(max)/MIC ratios of 45.0 and AUC(24h)/MIC values of 174.7 h, based on serum MICs, for both bacterial species. Using bacterial time-kill curves, generated ex vivo for serum marbofloxacin concentrations, PK-PD modelling established three levels of growth inhibition: AUC(24 h)/MIC ratios for no reduction, 3 log(10) and 4 log(10) reductions in bacterial count from the initial inoculum count were 41.9, 59.5 and 68.0 h for M. haemolytica and 48.6, 64.9 and 74.8 h for P. multocida, on average respectively. Inter-strain variability for 3 log(10) and 4 log(10) reductions in bacterial count was smaller for P. multocida than for M. haemolytica. In conjunction with literature data on MIC(90) values, the present results allowed prediction of dosages for efficacy for each organism for the three levels of growth inhibition.

Influence of oxytetracycline on carprofen pharmacodynamics and pharmacokinetics in calves

A tissue cage model of inflammation in calves was used to determine the pharmacokinetic and pharmacodynamic properties of individual carprofen enantiomers, following the administration of the racemate. RS(±) carprofen was administered subcutaneously both alone and in combination with intramuscularly administered oxytetracycline in a four-period crossover study. Oxytetracycline did not influence the pharmacokinetics of R(-) and S(+) carprofen enantiomers, except for a lower maximum concentration (Cmax ) of S(+) carprofen in serum after co-administration with oxytetracycline. S(+) enantiomer means for area under the serum concentration-time curve (AUC0-96 h were 136.9 and 128.3 μg·h/mL and means for the terminal half-life (T(1/2) k10 ) were = 12.9 and 17.3 h for carprofen alone and in combination with oxytetracycline, respectively. S(+) carprofen AUC0-96 h in both carprofen treatments and T(1/2) k10 for carprofen alone were lower (P < 0.05) than R(-) carprofen values, indicating a small degree of enantioselectivity in the disposition of the enantiomers. Carprofen inhibition of serum thromboxane B2 ex vivo was small and significant only at a few sampling times, whereas in vivo exudate prostaglandin (PG)E2 synthesis inhibition was greater and achieved overall significance between 36 and 72 h (P < 0.05). Inhibition of PGE2 correlated with mean time to achieve maximum concentrations in exudate of 54 and 42 h for both carprofen treatments for R(-) and S(+) enantiomers, respectively. Carprofen reduction of zymosan-induced intradermal swelling was not statistically significant. These data provide a basis for the rational use of carprofen with oxytetracycline in calves and indicate that no alteration to carprofen dosage is required when the drugs are co-administered.