Importance of relative binding of bisphenol A and bisphenol S to plasma proteins for predicting their in vivo potencies.

Many studies suggest that the potential impact of bisphenol S (BPS) as an endocrine disruptor is comparable to that of bisphenol A (BPA). However, in vitro-to-in vivo and from animal to human extrapolations require knowledge of the plasma free fraction of the active endocrine compounds. The present study aimed to characterise BPA and BPS binding to plasma proteins both in humans and different animal species. The plasma protein binding of BPA and BPS was assessed by equilibrium dialysis in plasma from adult female mice, rats, monkeys, early and late pregnant women as well as paired cord blood, early and late pregnant sheep and foetal sheep. The fraction of free BPA was independent of plasma concentrations and ranged between 4% and 7% in adults. This fraction was 2 to 3.5 times lower than that of BPS in all species except sheep, ranging from 3% to 20%. Plasma binding of BPA and BPS was not affected by the stage of pregnancy, BPA and BPS free fractions representing about 4% and 9% during early and late human pregnancy, respectively. These fractions were lower than the free fractions of BPA (7%) and BPS (12%) in cord blood. Our results suggest that similarly to BPA, BPS is extensively bound to proteins, mainly albumin. The higher fraction of free BPS compared to BPA may have implications for human exposure assessment since BPS free plasma concentrations are expected to be 2 to 3.5 times higher than that of BPA for similar plasma concentration.

Rational determination of cefazolin dosage regimen in horses based on pharmacokinetics/pharmacodynamics principles and Monte Carlo simulations.

A pharmacokinetics/pharmacodynamics (PK/PD) approach was used to determine the best empirical dosage regimen of cefazolin (CEZ) after intramuscular (IM) administration of CEZ in horses. Seven horses received a single IM or intravenous (IV) administration of CEZ of 5 mg/kg bodyweight (BW) according to a crossover design. CEZ plasma concentrations were measured using LC-MS/MS. The plasma concentrations in these seven horses and those of six other horses obtained in a previous study with an IV CEZ dose of 10 mg/kg were modelled simultaneously using NonLinear Mixed-Effect modelling followed by Monte Carlo simulations to establish a rational dosage regimen. A 90% Probability of Target Attainment (PTA) for a PK/PD target of a free plasma concentration exceeding MIC90 (fT > MIC ) for 40% of the dosing interval was set for selecting an effective dosing regimen. The typical half-life of absorption and bioavailability after IM administration were 1.25 h and 96.8%, respectively. A CEZ dosage regimen of 5 mg/kg BW q12h IM administration achieved therapeutic concentrations to control both Streptococcus zooepidemicus and Staphylococcus aureus. For the same dose, the fT > MIC after IM administration was significantly longer than after IV administration, and the IM route should be favoured by clinicians for its efficiency and convenience.

Doxycycline serum protein binding in pigs reveals a relatively high free fraction.

Doxycycline is an antibiotic widely used in pig farming. As with all antibiotics, only the free concentrations are considered to be bacteriologically active. Historically, the free fraction (fu) in pig plasma has been estimated at 7%, which, given the effective dosage regime used in pigs, leads to free plasma concentrations of doxycycline largely lower than the minimum inhibitory concentrations of the target pathogens. This apparent inconsistency led us to reassess plasma protein binding of doxycycline in pigs. Using an equilibrium dialysis method, the extent of doxycycline binding was measured individually in 26 pigs for total doxycycline concentration ranging from 10 to 1000 µmol/L. Analysis of the data using a non-linear mixed-effects model demonstrated linearity of plasma protein binding with a mean fu value of 31% and a relatively low inter-subject variability of approximately 10%. This new data showing that the free fraction is four times greater than what could have been anticipated from historical data is discussed in particular for the calculation of the PK/PD cut-offs, which are used to establish the clinical breakpoints for antimicrobial susceptibility testing.

Quantitative Pharmacodynamic Characterization of Resistance versus Heteroresistance of Colistin in E. coli Using a Semimechanistic Modeling of Killing Curves.

Heteroresistance corresponds to the presence, in a bacterial isolate, of an initial small subpopulation of bacteria characterized by a significant reduction in their sensitivity to a given antibiotic. Mechanisms of heteroresistance versus resistance are poorly understood. The aim of this study was to explore heteroresistance in mcr-positive and mcr-negative Escherichia coli strains exposed to colistin by use of modeling killing curves with a semimechanistic model. We quantify, for a range of phenotypically (susceptibility based on MIC) and genotypically (carriage of mcr-1 or mcr-3 or mcr-negative) different bacteria, a maximum killing rate (Emax) of colistin and the corresponding potency (EC50), i.e., the colistin concentrations corresponding to Emax/2. Heteroresistant subpopulations were identified in both mcr-negative and mcr-positive E. coli as around 0.06% of the starting population. Minority heteroresistant bacteria, both for mcr-negative and mcr-positive strains, differed from the corresponding dominant populations only by the maximum killing rate of colistin (differences for Emax by a factor of 12.66 and 3.76 for mcr-negative and mcr-positive strains, respectively) and without alteration of their EC50s. On the other hand, the resistant mcr-positive strains are distinguished from the mcr-negative strains by differences in their EC50, which can reach a factor of 44 for their dominant population and 22 for their heteroresistant subpopulations. It is suggested that the underlying physiological mechanisms differ between resistance and heteroresistance, with resistance being linked to a decrease in the affinity of colistin for its site of action, whereas heteroresistance would, rather, be linked to an alteration of the target, which will be more difficult to be further changed or destroyed.

Pharmacology, safety, efficacy and clinical uses of the COX-2 inhibitor robenacoxib.

Robenacoxib is a veterinary-approved non-steroidal anti-inflammatory drug (NSAID) of the coxib group. It possesses anti-hyperalgesic, anti-inflammatory and anti-pyretic properties. Robenacoxib inhibits the cyclooxygenase (COX)-2 isoform of COX selectively (in vitro IC50 ratios COX-1:COX-2, 129:1 in dogs, 32:1 in cats). At registered dosages (2 mg/kg subcutaneously in dogs and cats, 1-4 mg/kg orally in dogs and 1-2.4 mg/kg orally in cats), robenacoxib produces significant inhibition of COX-2 whilst sparing COX-1. The pharmacokinetic (PK) profile of robenacoxib is characterized by a high degree of binding to plasma proteins (>98%) and moderate volume of distribution (at steady state, 240 ml/kg in dogs and 190 ml/kg in cats). In consequence, the terminal half-life in blood (<2 h) is short, despite moderate body clearance (0.81 L/kg/h) in dogs and low clearance (0.44 L/kg/h) in cats. Excretion is principally in the bile (65% in dogs and 72% in cats). Robenacoxib concentrates in inflamed tissues, and clinical efficacy is achieved with once-daily dosing, despite the short blood terminal half-life. In dogs, no relevant breed differences in robenacoxib PK have been detected. Robenacoxib has a wide safety margin; in healthy laboratory animals daily oral doses 20-fold (dog, 1 month), eight-fold (cat, 6 weeks) and five-fold (dog, 6 months) higher than recommended clinical doses were well tolerated. Clinical efficacy and safety have been demonstrated in orthopaedic and soft tissue surgery, and in musculoskeletal disorders in dogs and cats.

Evaluating a tylosin dosage regimen for treatment of Staphylococcus delphini infection in mink (Neovison vison): a pharmacokinetic-pharmacodynamic approach.

Staphylococcus delphini is one of the most common pathogens isolated from mink infections, especially dermatitis. Tylosin (TYL) is used frequently against these infections, although no evidence-based treatment regimen exists. This study aimed to explore the dosage of TYL for infections caused by S. delphini in mink. Two animal experiments with a total of 12 minks were conducted to study the serum pharmacokinetic (PK) characteristics of TYL in mink after 10 mg/kg IV and oral dosing, respectively. The concentration of TYL in serum samples collected before and eight times during 24 h after TYL administration was quantitated with liquid chromatography quadrupole time-of-flight mass spectrometry, and the TYL disposition was analyzed using non-linear mixed effect analysis. The pharmacodynamics (PD) of TYL against S. delphini were studied using semi-mechanistic modeling of in vitro time-kill experiments. PKPD modeling and simulation were done to establish the PKPD index and dosage regimen. The disposition of TYL was described by a two-compartmental model. The area under the free concentration-time curve of TYL over the minimum inhibitory concentration of S. delphini (fAUC/MIC) was determined as PKPD index with breakpoints of 48.9 and 98.7 h for bacteriostatic and bactericidal effect, respectively. The calculated daily oral dose of TYL was 2378 mg/kg, which is 238-fold higher than the currently used TYL oral dosage regimen in mink (10 mg/kg). Accordingly, sufficient TYL concentrations are impossible to achieve in mink plasma, and use of this drug for extra-intestinal infections in this animal species must be discouraged.

Dynamic interactions between cephalexin and macrophages on different Staphylococcus aureus inoculum sizes: a tripartite in vitro model.

BACKGROUND: The bactericidal activity of an antimicrobial drug is generally assessed by in vitro bacterial time-kill experiments which do not include any components of the immune system, even though the innate immunity, the primary host defence, is probably able to kill a large proportion of pathogenic bacteria in immunocompetent patients. We developed an in vitro tripartite model to investigate the joint action of C57Bl/6 murine bone-marrow-derived macrophages and cephalexin on the killing of Staphylococcus aureus. RESULTS: By assessing the bactericidal effects on four bacterial inoculum sizes, we showed that macrophages can cooperate with cephalexin on inoculum sizes lower than 106 CFU/mL and conversely, protect S. aureus from cephalexin killing activity at the highest inoculum size. Cell analysis by flow cytometry revealed that macrophages were rapidly overwhelmed when exposed to large inoculums. Increasing the initial inoculum size from 105 to 107 CFU/mL increased macrophage death and decreased their ability to kill bacteria from six hours after exposure to bacteria. The addition of cephalexin at 16-fold MIC to 105 and 106 CFU/mL inoculums allowed the macrophages to survive and to maintain their bactericidal activity as if they were exposed to a small bacterial inoculum. However, with the highest inoculum size of 107 CFU/mL, the final bacterial counts in the supernatant were higher with macrophages plus cephalexin than with cephalexin alone. CONCLUSIONS: These results suggest that if the bacterial population at the infectious site is low, as potentially encountered in the early stage of infection or at the end of an antimicrobial treatment, the observed cooperation between macrophages and cephalexin could facilitate its control.

A history of antimicrobial drugs in animals: Evolution and revolution.

The evolutionary process of antimicrobial drug (AMD) uses in animals over a mere eight decades (1940-2020) has led to a revolutionary outcome, and both evolution and revolution are ongoing, with reports on a range of uses, misuses and abuses escalating logarithmically. As well as veterinary therapeutic perspectives (efficacy, safety, host toxicity, residues, selection of drug, determination of dose and measurement of outcome in treating animal diseases), there are also broader, nontherapeutic uses, some of which have been abandoned, whilst others hopefully will soon be discontinued, at least in more developed countries. Although AMD uses for treatment of animal diseases will continue, it must: (a) be sustainable within the One Health paradigm; and (b) devolve into more prudent, rationally based therapeutic uses. As this review on AMDs is published in a Journal of Pharmacology and Therapeutics, its scope has been made broader than most recent reviews in this field. Many reviews have focused on negative aspects of AMD actions and uses, especially on the question of antimicrobial resistance. This review recognizes these concerns but also emphasizes the many positive aspects deriving from the use of AMDs, including the major research-based advances underlying both the prudent and rational use of AMDs. It is structured in seven sections: (1) Introduction; (2) Sulfonamide history; (3) Nontherapeutic and empirical uses of AMDs (roles of agronomists and veterinarians); (4) Rational uses of AMDs (roles of pharmacologists, clinicians, industry and regulatory controls); (5) Prudent use (residue monitoring, antimicrobial resistance); (6) International and inter-disciplinary actions; and (7) Conclusions.

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

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

Validating an empiric sulfadiazine-trimethoprim dosage regimen for treatment of Escherichia coli and Staphylococcus delphini infections in mink (Neovison vison).

Antimicrobial agents are used extensively off-label in mink, as almost no agents are registered for this animal species. Pharmacokinetic (PK) and pharmacodynamic (PD) data are required to determine antimicrobial dosages specifically targeting mink bacterial pathogens. The aims of this study were to assess, in a PKPD framework, the empirical dosage regimen for a combination of trimethoprim (TMP) and sulfadiazine (SDZ) in mink, and secondarily to produce data for future setting of clinical breakpoints. TMP and SDZ PK parameters were obtained experimentally in 22 minks following IV or oral administration of TMP/SDZ (30 mg/kg, i.e. 5 mg/kg TMP and 25 mg/kg SDZ). fAUC/MIC with a target value of 24 hr was selected as the PKPD index predictive of TMP/SDZ efficacy. Using a modeling approach, PKPD cutoffs for TMP and SDZ were determined as 0.062 and 16 mg/L, respectively. By incorporating an anticipated potentiation effect of SDZ on TMP against Escherichia coli and Staphylococcus delphini, the PKPD cutoff of TMP was revised to 0.312 mg/L, which is above the tentative epidemiological cutoffs (TECOFF) for these species. The current empirical TMP/SDZ dosage regimen (30 mg/kg, PO, once daily) therefore appears adequate for treatment of wild-type E. coli and S. delphini infections in mink.

Kinetic disposition of diazepam and its metabolites after intravenous administration of diazepam in the horse: Relevance for doping control.

In horses, the benzodiazepine diazepam (DIA) is used as sedative for pre-medication or as an anxiolytic to facilitate horse examinations. As the sedative effects can also be abused for doping purposes, DIA is prohibited in equine sports. DIA is extensively metabolized to several active metabolites such as nordazepam, temazepam and oxazepam (OXA). For veterinarians, taking into account the detection times of DIA and its active metabolites is needed for minimizing the risk of an anti-doping rule violation. Therefore, a pharmacokinetic study on 6 horses was conducted using a single intravenous (IV) dose of 0.2 mg/kg DIA Plasma and urine samples were collected at specified intervals until 16 and 26 days post-administration, respectively. Samples were analysed by a sensitive liquid chromatography-electrospray ionization/tandem mass spectrometry method. DIA showed a triphasic elimination pattern in the horse. The mean plasma clearance of DIA was 5.9 ml/min/kg, and the plasma elimination half-life in the terminal phase was 19.9 h. Applying the Toutain model approach, an effective plasma concentration of DIA was estimated at 24 ng/ml, and irrelevant plasma concentration (IPC) and irrelevant urine concentration (IUC) were computed to 0.047 and 0.1 ng/ml, respectively. The detection time according to the European Horserace Scientific Liaison Committee (EHSLC), that is the time for which observed DIA plasma concentrations of all investigated horses were below the IPC was 10 days. Using Monte Carlo Simulations, it was estimated that concentrations of DIA in plasma would fall below the IPC 18 days after the DIA administration for 90% of horses. However, in the present study, a single administration of DIA could be detected for 24 days in urine via the presence of OXA, its dominant metabolite.

Toxicokinetics of bisphenol S in rats for predicting human bisphenol S clearance from allometric scaling.

Previous data obtained in piglets suggested that despite structural analogy with Bisphenol A (BPA), Bisphenol S (BPS) elimination may proceed more slowly, resulting in a much higher systemic exposure to unconjugated BPS than to BPA. Interspecies allometric scaling was applied to predict the toxicokinetic (TK) parameters of BPS, namely plasma clearance in humans from values obtained in animals, and thus contribute to assessment of the human internal exposure to BPS. Allometric scaling was performed using mean BPS plasma clearance values measured in rats after intravenous administration of 5 mg BPS /kg body weight (BW) and those previously obtained in piglets and sheep using identical IV BPS dosing and analytical procedures. The BPS plasma clearance, evaluated at 0.92 L/kg.h in rats, was proportional to species body weight, enabling the prediction of human BPS plasma clearance by extrapolating to a BW of 70 kg. The estimated BPS plasma clearance in humans was thus 0.92 L/min (0.79 L/kg.h), i.e. about two times lower than the previously estimated BPA clearance (1.79 L/min). By increasing systemic exposure to the active moiety of an environmental estrogenic chemical, this less efficient clearance of BPS in humans, as compared with BPA, might worsen the harmful consequences of replacing BPA by BPS.

Differential susceptibility to tetracycline, oxytetracycline and doxycycline of the calf pathogens Mannheimia haemolytica and Pasteurella multocida in three growth media.

For clinical isolates of bovine Mannheimia haemolytica and Pasteurella multocida, this study reports minimum inhibitory concentration (MIC) differences for tetracycline, oxytetracycline and doxycycline between cation-adjusted Mueller-Hinton broth (CAMHB), foetal bovine serum (FBS) and Roswell Park Memorial Institute (RPMI) medium. MICs were determined according to CLSI standards and additionally using five overlapping sets of twofold dilutions. Matrix effect: (a) free drug MICs and minimum bactericidal concentrations (MBC) for all drugs were significantly higher in FBS than in CAMHB for both pathogens (p < 0.001); (b) MICs and MBCs were higher for CAMHB and FBS compared to RPMI for P. multocida only. Net growth rate for P. multocida in CAMHB was significantly slower than in FBS and higher than in RPMI, correlating to MIC and MBC ranking. Drug effect: doxycycline MICs and MBCs were significantly lower (p < 0.001) in both CAMHB and FBS than tetracycline and oxytetracycline for both pathogens. Only for M. haemolytica were oxytetracycline MIC and MBC significantly lower than tetracycline, precluding the use of tetracycline to predict oxytetracycline susceptibility in this species. Determining potencies of tetracyclines in a physiological medium, such as FBS, is proposed, when the objective is correlation with pharmacokinetic data for dosage determination.

Impact of Low and High Doses of Marbofloxacin on the Selection of Resistant Enterobacteriaceae in the Commensal Gut Flora of Young Cattle: Discussion of Data from 2 Study Populations.

In the context of requested decrease of antimicrobial use in veterinary medicine, our objective was to assess the impact of two doses of marbofloxacin administered on young bulls (YBs) and veal calves (VCs) treated for bovine respiratory disease, on the total population of Enterobacteriaceae in gut flora and on the emergence of resistant Enterobacteriaceae. In two independent experiments, 48 YBs from 6 commercial farms and 33 VCs previously colostrum deprived and exposed to cefquinome were randomly assigned to one of the three groups LOW, HIGH, and Control. In LOW and HIGH groups, animals received a single injection of, respectively, 2 and 10 mg/kg marbofloxacin. Feces were sampled before treatment, and at several times after treatment. Total and resistant Enterobacteriaceae enumerating were performed by plating dilutions of fecal samples on MacConkey agar plates that were supplemented or not with quinolone. In YBs, marbofloxacin treatment was associated with a transient decrease in total Enterobacteriaceae count between day (D)1 and D3 after treatment. Total Enterobacteriaceae count returned to baseline between D5 and D7 in all groups. None of the 48 YBs harbored marbofloxacin-resistant Enterobacteriaceae before treatment. After treatment, 1 out of 20 YBs from the Control group and 1 out of 14 YBs from the HIGH group exhibited marbofloxacin-resistant Enterobacteriaceae. In VCs, the rate of fluoroquinolone-resistant Enterobacteriaceae significantly increased after low and high doses of marbofloxacin treatment. However, the effect was similar for the two doses, which was probably related to the high level of resistant Enterobacteriaceae exhibited before treatment. Our results suggest that a single treatment with 2 or 10 mg/kg marbofloxacin exerts a moderate selective pressure on commensal Enterobacteriaceae in YBs and in VCs. A fivefold decrease of marbofloxacin regimen did not affect the selection of resistances among commensal bacteria.

Diagnostic microbiology in veterinary dermatology: present and future.

BACKGROUND: The microbiology laboratory can be perceived as a service provider rather than an integral part of the healthcare team. OBJECTIVES: The aim of this review is to discuss the current challenges of providing a state-of-the-art diagnostic veterinary microbiology service including the identification (ID) and antimicrobial susceptibility testing (AST) of key pathogens in veterinary dermatology. METHODS: The Study Group for Veterinary Microbiology (ESGVM) of the European Society of Clinical Microbiology and Infectious Diseases (ESCMID) identified scientific, technological, educational and regulatory issues impacting the predictive value of AST and the quality of the service offered by microbiology laboratories. RESULTS: The advent of mass spectrometry has significantly reduced the time required for ID of key pathogens such as Staphylococcus pseudintermedius. However, the turnaround time for validated AST methods has remained unchanged for many years. Beyond scientific and technological constraints, AST methods are not harmonized and clinical breakpoints for some antimicrobial drugs are either missing or inadequate. Small laboratories, including in-clinic laboratories, are usually not adequately equipped to run up-to-date clinical microbiologic diagnostic tests. CONCLUSIONS AND CLINICAL IMPORTANCE: ESGVM recommends the use of laboratories employing mass spectrometry for ID and broth micro-dilution for AST, and offering assistance by expert microbiologists on pre- and post-analytical issues. Setting general standards for veterinary clinical microbiology, promoting antimicrobial stewardship, and the development of new, validated and rapid diagnostic methods, especially for AST, are among the missions of ESGVM.

Conjugation and deconjugation reactions within the fetoplacental compartment in a sheep model: a key factor determining bisphenol A fetal exposure.

The widespread human exposure to bisphenol A (BPA), an endocrine disruptor targeting developmental processes, underlines the need to better understand the mechanisms of fetal exposure. Animal studies have shown that at a late stage of pregnancy BPA is efficiently conjugated by the fetoplacental unit, mainly into BPA-glucuronide (BPA-G), which remains trapped within the fetoplacental unit. Fetal exposure to BPA-G might in turn contribute to in situ exposure to bioactive BPA, following its deconjugation into parent BPA at the level of fetal sensitive tissues. The objectives of our study were 1) to characterize the BPA glucurono- and sulfoconjugation capabilities of the ovine fetal liver at different developmental stages, 2) to compare hepatic conjugation activities in human and sheep, and 3) to evaluate the extent of BPA conjugation and deconjugation processes in placenta and fetal gonads. At an early stage of pregnancy, and despite functional sulfoconjugation activity, ovine fetuses expressed low hepatic BPA conjugation capabilities, suggesting that this stage of development represents a critical window in terms of BPA exposure. Conversely, the late ovine fetus expressed an efficient detoxification system that metabolized BPA into BPA-G. Hepatic glucuronidation activities were quantitatively similar in adult sheep and humans. In placenta, BPA conjugation and BPA-G deconjugation activities were relatively balanced, whereas BPA-G hydrolysis was systematically higher than BPA conjugation in gonads. The possible reactivation of BPA-G into BPA could contribute to an increased exposure of fetal sensitive tissues to bioactive BPA in situ.

Allometric scaling for predicting human clearance of bisphenol A.

The investigation of interspecies differences in bisphenol A (BPA) pharmacokinetics (PK) may be useful for translating findings from animal studies to humans, identifying major processes involved in BPA clearance mechanisms, and predicting BPA PK parameters in man. For the first time, a large range of species in terms of body weight, from 0.02 kg (mice) to 495 kg (horses) was used to predict BPA clearance in man by an allometric approach. BPA PK was evaluated after intravenous administration of BPA in horses, sheep, pigs, dogs, rats and mice. A non-compartmental analysis was used to estimate plasma clearance and steady state volume of distribution and predict BPA PK parameters in humans from allometric scaling. In all the species investigated, BPA plasma clearance was high and of the same order of magnitude as their respective hepatic blood flow. By an allometric scaling, the human clearance was estimated to be 1.79 L/min (equivalent to 25.6 mL/kg.min) with a 95% prediction interval of 0.36 to 8.83 L/min. Our results support the hypothesis that there are highly efficient and hepatic mechanisms of BPA clearance in man.

Low or high doses of cefquinome targeting low or high bacterial inocula cure Klebsiella pneumoniae lung infections but differentially impact the levels of antibiotic resistance in fecal flora.

The combination of efficacious treatment against bacterial infections and mitigation of antibiotic resistance amplification in gut microbiota is a major challenge for antimicrobial therapy in food-producing animals. In rats, we evaluated the impact of cefquinome, a fourth-generation cephalosporin, on both Klebsiella pneumoniae lung infection and intestinal flora harboring CTX-M-producing Enterobacteriaceae. Germfree rats received a fecal flora specimen from specific-pathogen-free pigs, to which a CTX-M-producing Escherichia coli strain had been added. K. pneumoniae cells were inoculated in the lungs of these gnotobiotic rats by using either a low (10(5) CFU) or a high (10(9) CFU) inoculum. Without treatment, all animals infected with the low or high K. pneumoniae inoculum developed pneumonia and died before 120 h postchallenge. In the treated groups, the low-inoculum rats received a 4-day treatment of 5 mg/kg of body weight cefquinome beginning at 24 h postchallenge (prepatent phase of the disease), and the high-inoculum rats received a 4-day treatment of 50 mg/kg cefquinome beginning when the animals expressed clinical signs of infection (patent phase of the disease). The dose of 50 mg/kg targeting the high K. pneumoniae inoculum cured all the treated rats and resulted in a massive amplification of CTX-M-producing Enterobacteriaceae. A dose of 5 mg/kg targeting the low K. pneumoniae inoculum cured all the rats and averted an outbreak of clinical disease, all without any amplification of CTX-M-producing Enterobacteriaceae. These findings might have implications for the development of new antimicrobial treatment strategies that ensure a cure for bacterial infections while avoiding the amplification of resistance genes of human concern in the gut microbiota of food-producing animals.

Should oral gavage be abandoned in toxicity testing of endocrine disruptors?

For decades, hazard assessments for environmental chemicals have used intra-gastric gavage to assess the effects of 'oral' exposures. It is now widely used--and in some cases required--by US federal agencies to assess potential toxicity of endocrine disrupting chemicals (EDCs). In this review we enumerate several reasons why gavage is not appropriate for the assessment of EDCs using bisphenol A (BPA) as a main example. First, whereas human dietary exposures interact with the oral mucosa, gavage exposures avoid these interactions, leading to dramatic differences in absorption, bioavailability and metabolism with implications for toxicokinetic assumptions and models. Additionally, there are well acknowledged complications associated with gavage, such as perforation of the esophagus that diminish its value in toxicological experiments. Finally, the gavage protocol itself can induce stress responses by the endocrine system and confound the assessment of EDCs. These serious flaws have not been taken into account in interpreting results of EDC research. We propose the exploration of alternatives to mimic human exposures when there are multiple exposure routes/sources and when exposures are chronic. We conclude that gavage may be preferred over other routes for some environmental chemicals in some circumstances, but it does not appropriately model human dietary exposures for many chemicals. Because it avoids exposure pathways, is stressful, and thus interferes with endocrine responses, gavage should be abandoned as the default route of administration for hazard assessments of EDCs.

Why the racing industry and equestrian disciplines need to implement population pharmacokinetics: To learn, explain, summarize, harmonize, and individualize.

Population pharmacokinetics (POP PK) is a powerful pharmacokinetic tool, which measures quantitatively, and explains the variability in drug exposure and drug effect between individuals. POP PK uses an observational (nonexperimental) approach; it is conducted in the target population living in its normal environment (e.g., farm and race-track). The strength of the POP PK approach lies in its greater relevance for the population studied in its different natural environments than experimental studies carried out in more or less biased laboratory conditions. In clinical settings, it is commonly necessary to restrict the number of samples per subject collected for analysis and the derived data cannot be analyzed using traditional individual data analytical methods; rather data are merged and analyzed with an appropriate statistical tool: the nonlinear mixed effect model (NLMEM). POP PK modeling is frequently used with the objective of adjusting drug dosage, and hence drug exposure, not only for the whole population but also for subgroups of animals (e.g., for a given breed, sex, and age). It can also have application at the individual subject level, in the context of precision medicine. For horses, the use of the POP PK/PD model will allow prescribers to estimate an individual Withdrawal Time for a given horse whose treatment they are supervising. Another potential field of application will be meta-analysis of existing data to generate new knowledge on a drug or to collate and synthesize, in an objective and transparent manner, existing data; this will facilitate harmonization of screening limits at an international level.