Dose regimen optimization of cephalothin for surgical prophylaxis against Staphylococcus aureus and coagulase negative staphylococci in dogs by pharmacokinetic/pharmacodynamic modeling.

First generation cephalosporins such cephalothin of cefazolin are indicated for antimicrobial prophylaxis for clean and clean contaminated surgical procedures because its antimicrobial spectrum, relative low toxicity and cost. Anesthesia and surgery could alter the pharmacokinetic behavior of different drugs administered perioperative by many mechanisms that affect distribution, metabolism or excretion processes. Intravenous administration of the antimicrobial within 30 and 60 min before incision is recommended in order to reach therapeutic serum and tissue concentrations and redosing is recommended if the duration of the procedure exceeds two half-life of the antimicrobial. To the author's knowledge there are no pharmacokinetic studies of cephalothin in dogs under anesthesia/surgery conditions. The aim of this study was (1) to evaluate the pharmacokinetics of cephalothin in anesthetized dogs undergoing ovariohysterectomy by a nonlinear mixed-effects model and to determine the effect of anesthesia/surgery and other individual covariates on its pharmacokinetic behavior; (2) to determine the MIC and conduct a pharmacodynamic modeling of time kill curves assay of cephalothin against isolates of Staphylococcus spp. isolated from the skin of dogs; (3) to conduct a PK/PD analysis by integration of the obtained nonlinear mixed-effects models in order to evaluate the antimicrobial effect of changing concentrations on simulated bacterial count; and (4) to determine the PK/PD endpoints and PK/PDco values in order to predict the optimal dose regimen of cephalothin for antimicrobial prophylaxis in dogs. Anesthesia/surgery significantly reduced cephalothin clearance by 18.78%. Based on the results of this study, a cephalothin dose regimen of 25 mg/kg q6h by intravenous administration showed to be effective against Staphylococcus spp. isolates with MIC values ≤2 µg/mL and could be recommended for antimicrobial prophylaxis for clean surgery in healthy dogs.

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.

Effects of Growth Medium and Inoculum Size on Pharmacodynamics Activity of Marbofloxacin against Staphylococcus aureus Isolated from Caprine Clinical Mastitis.

Staphylococcus aureus (S. aureus) is an important pathogen that causes clinical mastitis in goats and produces infections difficult to cure. Different antimicrobials as fluoroquinolones have been used against S. aureus. However, the studies developed to evaluate the bacterial drug interaction only have used the MIC as a single reference point with artificial growth media. The aims of this study were to describe the effect of marbofloxacin on S. aureus isolated from mastitis goats' milk by different approaches as the minimum inhibitory and bactericidal concentrations (MIC and MBC) in cation adjusted Mueller-Hinton broth (CAMHB), serum and milk of goats at two inoculum sizes of 105 and 108 CFU/mL, the determination and analysis of the time kill curves (TKC) by non-linear mixed effect models in each growth medium and inoculum size, as well as the estimation of their pharmacokinetics/pharmacodynamics (PK/PD) cutoff values. The results obtained indicate that MIC values were higher and increases 2,4-fold in serum and 3,6-fold in milk at high inoculum, as well as the EC50 values determined by each pharmacodynamics model. Finally, the PK/PD cutoff values defined as fAUC24/MIC ratios to achieve clinical efficacy were highly dependent on inoculum and growth medium, with median values of 60-180, especially at high inoculum in milk, suggesting that further studies are necessary to evaluate and optimize the best therapeutic strategies for treating S. aureus in lactating goats.

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

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.

Comparative pharmacokinetics and pharmacokinetic/pharmacodynamic analysis by nonlinear mixed-effects modeling of cefquinome in nonpregnant, pregnant, and lactating goats after intravenous and intramuscular administration.

Cefquinome is a fourth-generation cephalosporin that is used empirically in goats. Different physiologic factors like pregnancy or lactation could determine the pharmacokinetic behavior of drugs in the organism. The objectives of this study are to (a) compare the pharmacokinetics of cefquinome after intravenous and intramuscular administration in adult nonpregnant (n = 6), pregnant (n = 6), and lactating goats (n = 6), at a dose of 2 mg/kg, with rich sampling by nonlinear mixed-effects modeling, (b) conduct a pharmacokinetic/pharmacodynamic analysis to evaluate the efficacy of the recommended posology in goats with different physiological states, and (c) determine the optimal posology that achieve a PTA value ≥ 90%, taking into account a T > MIC ≥ 60% of a MIC value ≤ 0.25 µg/ml, in the different subpopulations of goats for both routes. Gestation significantly increased Ka and V1, while reduced F0, Cl, and Q. On the other hand, lactation significantly increased V1 and reduced Tk0. Cefquinome concentrations achieved in placental cotyledon, amniotic fluid, and fetal serum indicate a minimal penetration across the placental barrier. Moreover, milk penetration of cefquinome was minimal. The total body clearance of cefquinome for goats was 0.29 L kg-1  hr-1 , that is apparently higher than the reported for cows (0.13 L kg-1  hr-1 ) and pigs (0.16 L kg-1  hr-1 ). So, the optimal dose regimen for cefquinome after intravenous and intramuscular administration required higher dose and frequency of administration compared with recommendations for cows or pigs. Therefore, 2 mg kg-1  8 hr-1 and 5 mg kg-1  12 hr-1 could be used for IV and IM routes, respectively, for the treatment of respiratory infections caused by P. multocida and M. haemolytica, but only 5 mg kg-1  12 hr-1 by both routes should be recommended for Escherichia coli infections.

Anti-tuberculosis site-specific oral delivery system that enhances rifampicin bioavailability in a fixed-dose combination with isoniazid.

The in vivo release segregation of rifampicin (RIF) and isoniazid (INH) has been proposed as a strategy to avoid RIF acid degradation, which is known as one of the main factors for reduced RIF bioavailability and can result in drug-resistant tuberculosis. So far, this strategy has been scarcely explored. The aims of this study were to investigate the stability and bioavailability of RIF after combination of a very fast release matrix of RIF with a sustained delivery system of INH. A series of INH-alginic acid complexes (AA-INH) was obtained and characterized. Independent and sequential release profile of AA-INH at biorrelevant media of pH 1.20 and 6.80 was explored. In addition, AA-INH was combined with a RIF-carboxymethylcellulose very fast release complex (CMC-RIF) obtained previously and subjected to acid dissolution assays to evaluate RIF acid stability and determine RIF and INH dissolution efficiencies. Finally, a pharmacokinetic study in dogs was carried out. The AA-INH was easily obtained in solid-state. Their characterization revealed its ionic nature, with a loading capacity of around 30%. The dissolution efficiencies (15 min) confirmed release segregation in acid media with 7.8 and 65.6% for AA-INH and CMC-RIF, respectively. INH release rate from the AA-INH system was slow in acid media and increased in simulated intestinal media. The complete release of INH was achieved after 2 h in simulated intestinal media in the sequential release experiments. The acid degradation of RIF was significantly reduced (36.7%) when both systems were combined and oral administration to dogs revealed a 42% increase in RIF bioavailability. In conclusion, CMC-RIF and AA-INH may be useful for the formulation of a site-specific solid dosage form to overcome some of the main obstacles in tuberculosis treatment. Graphical abstract.

Pharmacokinetic evaluation of marbofloxacin after intravenous administration at different ages in llama crias, and pharmacokinetic/pharmacodynamic analysis by Monte Carlo simulation.

In llama crias (tekes), Escherichia coli and Staphylococcus aureus are major pathogens, and marbofloxacin could be a suitable choice. The objectives of this study were (a) to evaluate the serum pharmacokinetics of marbofloxacin (5 mg/kg) after intravenous administration in tekes and simulate a multidose regimen; (b) to emulate pharmacokinetic profiles after single dose and steady-state conditions by Monte Carlo simulation (c) to determine the MIC of regional strains of Escherichia coli and Staphylococcus aureus; (d) to perform a PK/PD analysis by Monte Carlo simulation. Pharmacokinetics of marbofloxacin was evaluated in six animals at 3, 10, 24, 50, and 80 days after birth. Marbofloxacin were determined by HPLC. A steady-state multi-dose simulation was carried out, and concentration-time profiles were generated by Monte Carlo simulation. MIC of marbofloxacin against regional E. coli and S. aureus strains were also determined. Finally, a PK/PD analysis was conducted by Monte Carlo simulation. After pharmacokinetic analysis, clearance showed a trend to increase (0.14 and 0.18 L kg-1  hr-1 ), and AUC (36.74 and 15.21 µg hr-1  ml-1 ) and Vss (3.06 and 3.37 L/kg) trended to decrease at 3 and 80 days-old, respectively, showing accumulation ~50% in animals with 3 days. All strains tested of E. coli (MIC90  = 0.06 µg/ml) and S. aureus (MIC90  = 0.25 µg/ml) were susceptible to marbofloxacin. PK/PD analysis suggests that the therapeutic regimen of marbofloxacin could be effective for infections caused by E. coli strains in animals between 3 and 80 days, with a CFR for Cmax /MIC > 10 of 100% and for AUC24 /MIC > 125 of 99.99%; and for infections produced by S. aureus in animals between 3 and 24 days old, with a CFR for Cmax /MIC > 10 of 93.08% and for AUC24 /MIC > 60 of 97.01%, but a higher dose should be used in older animals, because PK/PD endpoints were not met.