Perioperative pharmacokinetics and pharmacodynamics of meloxicam in emus (Dromaius novaehollandiae) of different age groups using nonlinear mixed effect modelling

Meloxicam is a widely used nonsteroidal anti-inflammatory drug in avian species. However, variability in pharmacokinetic (PK) and pharmacodynamic (PD) parameters in birds warrants species-specific studies for dose and dosing interval optimization. We performed a perioperative PK study of meloxicam (0.5 mg/kg, intravenously) on emus of three different age groups: 3 chicks (5 weeks old, 3.5 kg), 4 juveniles (26 weeks old, 18.8 kg) and 6 adults (66 weeks old, 38.8 kg). A two-compartment population PK model including weight as a significant covariate on clearance and central volume of distribution (V1) best fitted the data. The typical values (20 kg bird) for clearance and V1 were 0.54 L/kg/h and 0.095 L/kg. Both parameters significantly decreased with increasing weight/age. Meloxicam potency and selectivity for COX-1 and COX-2 were measured in whole blood assays (TxB₂ production endpoint). Meloxicam was partially selective in emus (IC₅₀ COX-1:COX-2 = 9.1:1). At the current empirical dose (0.5 mg/kg/24 hr), plasma meloxicam concentration is above IC₅₀ of COX-2 for only 2 hr. PK/PD predicted dose required for 80% COX-2 inhibition over 24 hr were 3.4, 1.4 and 0.95 L/kg/day in chicks, juveniles and adult emus, respectively. The safety, therapeutic efficacy and practicality of modifying the daily dose or dose interval should be considered for dose recommendations in emus.

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.

Analysis of teaching methods in anaesthesia in the undergraduate curriculum of four veterinary universities

OBJECTIVE

To design a holistic audit tool to assess the effectiveness of anaesthesia teaching strategies, and thereby to study veterinary undergraduate teaching methods in different geographical areas.

STUDY DESIGN

Qualitative study using interviews of university staff and students to identify common themes and differences in teaching veterinary anaesthesia.

METHODS

An audit was performed using an audit tool in four veterinary universities (École Nationale Vétérinaire d'Alfort, France; Royal Veterinary College, UK; University of Buenos Aires, Argentina; and Alma mater studiorum - Università di Bologna, Italy). First, an open-question interview of anaesthesia head of service (60-90 minutes) identified the pedagogical strategies in order to conceive a subsequent semi-directive interview formulated as a SWOT analysis (Strength/Weaknesses/Opportunity/Threats). Second, the SWOT reflection was conducted by a second staff member and focussed on: 1) general organization; 2) topics for pre-rotation teaching; 3) teaching methods for clinical rotation; and 4) assessment methods. Qualitative analysis of the interview responses was performed with semi-structured interviews. Finally, the students evaluated their teaching through a students' questionnaire generated from the output of both interviews.

RESULTS

A group of nine lecturers and 106 students participated in the study at four different sites. Preclinical teaching ranged from 13 to 24 hours (median 15 hours). Clinical teaching ranged from 4 to 80 hours (median 60 hours). Overall, all faculties perceived time as a limitation and attempted to design strategies to achieve the curriculum expectations and optimize teaching using more time-efficient exercises. Large animal anaesthesia teaching was found to be a common area of weakness. Internal feedback was delivered to each university, whereas generalized results were shared globally.

CONCLUSIONS

This preliminary study proved the generalizability of the protocol used. Recruiting a larger pool of universities would help to identify and promote efficient teaching strategies and innovations for training competent new graduates in an ever-expanding curriculum.

Patterns of Limb and Epaxial Muscle Activity During Walking in the Fire Salamander, Salamandra salamandra

Salamanders and newts (urodeles) are often used as a model system to elucidate the evolution of tetrapod locomotion. Studies range from detailed descriptions of musculoskeletal anatomy and segment kinematics, to bone loading mechanics and inferring central pattern generators. A further area of interest has been in vivo muscle activity patterns, measured through electromyography (EMG). However, most prior EMG work has primarily focused on muscles of the forelimb or hindlimb in specific species or the axial system in others. Here we present data on forelimb, hindlimb, and epaxial muscle activity patterns in one species, Salamandra salamandra, during steady state walking. The data are calibrated to limb stride cycle events (stance phase, swing phase), allowing direct comparisons to homologous muscle activation patterns recorded for other walking tetrapods (e.g., lizards, alligators, turtles, mammals). Results demonstrate that Salamandra has similar walking kinematics and muscle activity patterns to other urodele species, but that interspecies variation does exist. In the forelimb, both the m. dorsalis scapulae and m. latissimus dorsi are active for 80% of the forelimb swing phase, while the m. anconaeus humeralis lateralis is active at the swing–stance phase transition and continues through 86% of the stance phase. In the hindlimb, both the m. puboischiofemoralis internus and m. extensor iliotibialis anterior are active for 30% of the hindlimb swing phase, while the m. caudofemoralis is active 65% through the swing phase and remains active for most of the stance phase. With respect to the axial system, both the anterior and posterior m. dorsalis trunci display two activation bursts, a pattern consistent with stabilization and rotation of the pectoral and pelvic girdles. In support of previous assertions, comparison of Salamandra muscle activity timings to other walking tetrapods revealed broad-scale similarities, potentially indicating conservation of some aspects of neuromuscular function across tetrapods. Our data provide the foundation for building and testing dynamic simulations of fire salamander locomotor biomechanics to better understand musculoskeletal function. They could also be applied to future musculoskeletal simulations of extinct species to explore the evolution of tetrapod locomotion across deep-time.

Population Pharmacokinetics and Pharmacodynamics Modeling of Torasemide and Furosemide After Oral Repeated Administration in Healthy Dogs

Torasemide is a loop diuretic licensed in dogs for cardiogenic pulmonary oedema. The aim of this pharmacokinetic-pharmacodynamic (PK/PD) study was to define an optimally effective dosage regimen based on preclinical data. In a first study, 5 dogs received once-daily oral torasemide (0, 0.1, 0.2, 0.4, 0.8 mg/kg/day) for 14 days. A second study compared once-daily oral torasemide (0, 0.1, 0.2, 0.3, 0.4 mg/kg/day) to twice-daily furosemide (1, 2, 4, 8 mg/kg/day). For all doses of the second study, 11 dogs received a first day of treatment, followed by a 3 day washout and resumed daily treatment for 10 days (until Day 14). Blood and urine were collected to measure urinary torasemide excretion and plasma torasemide concentrations and daily diuresis and natriuresis. Torasemide PK was linear. After rapid absorption (T_max 0.5–1 h), 61% of the bioavailable torasemide was eliminated unchanged in urine. Diuresis and natriuresis observed with torasemide were similar to the ones obtained after furosemide (daily dose-ratios: 1/20 to 1/10). The average diuresis increased from baseline (220 ± 53 mL/day for 10 kg dogs) to 730 ±120 mL after the first torasemide administration and up to 1150 ± 252 mL after 10 administrations at the highest dose. At higher doses (≥0.3 mg/kg/day), daily diureses after 10 diuretic treatment-days were higher than Day 1 and variable between dogs; in contrast, diureses remained constant over time and less variable for doses up to 0.2 mg/kg/day. Natriuresis peaked after the first day and decreased dramatically after the 2nd treatment-day then stabilized to a value close to baseline, except for 0.4 mg/kg/day. Urinary torasemide excretion predicted pharmacodynamics better than plasma concentrations. The decrease in natriuresis observed was successfully modeled using a resistance mechanism; this is likely due to a reabsorption of sodium which did not seem however to affect the volume of urine excreted. For a daily target diuresis of 460 mL/dog/day in severe pulmonary oedema (net fluid loss 240 mL/dog/day), a computed dose of 0.26 mg/kg/day (3.5 mg/kg/day furosemide-equivalent) was selected for clinical studies. Due to high inter-individual variability in diureses at doses ≥0.3 mg/kg, higher doses should be limited to 3–5 days to avoid supra-clinical effects in high responders.

A multicenter randomized controlled trial of medium-chain triglyceride dietary supplementation on epilepsy in dogs

Background

Medium‐chain triglyceride (MCT) enriched diet has a positive effect on seizure control and behavior in some dogs with idiopathic epilepsy (IE).

Objective

To evaluate the short‐term efficacy of MCTs administered as an add‐on dietary supplement (DS) to a variable base diet to assess seizure control and antiseizure drug's (ASD) adverse effect profiles.

Animals

Twenty‐eight dogs with International Veterinary Epilepsy Task Force Tier II (IVETF) level diagnosis of treated IE with 3 or more seizures in the last 3 months were used.

Methods

A 6‐month multicenter, prospective, randomized, double‐blinded, placebo‐controlled crossover trial was completed, comparing an MCT‐DS with a control‐DS. A 9% metabolic energy‐based amount of MCT or control oil was supplemented to the dogs' diet for 3 months, followed by a control oil or MCT for another 3 months, respectively. Dogs enrolled in this study satisfied most requirements of IE diagnosis stated by the IVETF II level. If they received an oil DS or drugs that could influence the metabolism of the investigated DS or chronic ASD, the chronic ASD medication was adjusted, or other causes of epilepsy were found, the dogs were excluded from the study.

Results

Seizure frequency (median 2.51/month [0‐6.67] versus 2.67/month [0‐10.45]; P = .02) and seizure‐day frequency were significantly (1.68/month [0‐5.60] versus 1.99/month [0‐7.42], P = .01) lower when dogs were fed MCT‐DS in comparison with the control‐DS. Two dogs were free of seizures, 3 had ≥50% and 12 had <50% reductions in seizure frequency, and 11 dogs showed no change or an increase in seizure frequency.

Conclusions and Clinical Importance

These data show antiseizure properties of an MCT‐DS compared to a control oil and support former evidence for the efficacy of MCTs as a nutritive, management option for a subpopulation of drug‐resistant dogs with epilepsy.

Faculty's Perception of a Research Project Embedded in the Undergraduate Veterinary Curriculum

In this article, we describe faculty's perception of a research project embedded in the final year of the undergraduate veterinary curriculum and look at factors associated with overall perceptions of the project. We hypothesized that faculty would have a dichotomous attitude toward the research project, with faculty viewing it either positively or negatively, and that this opinion of the project would be largely influenced by the background of the faculty member-in particular, her or his role at the Royal Veterinary College. We explored this hypothesis via a questionnaire consisting of 26 questions in categorical format, Likert-scale format, and ranking format. The questions addressed faculty demographics, faculty's perceptions of the project, and generic skills. Faculty had an overall positive view of the project and found it to be a useful part of the undergraduate curriculum (83.3% found it to be useful or very useful). Faculty's perception of the project was influenced by their role at the college (p = .017), the species with which they primarily work (p = .05), and their opinion on the time spent supervising the final-year project (p = .003). We concluded that faculty view research as an important and useful part of the undergraduate veterinary curriculum.

Relationship between serum iohexol clearance, serum SDMA concentration, and serum creatinine concentration in non-azotemic dogs

BACKGROUND

Serum creatinine and symmetric dimethylarginine (SDMA) are used as surrogate markers of glomerular filtration rate (GFR) in clinical practice. Data pertaining to the correlations between GFR, SDMA, and serum creatinine in client-owned dogs are limited.

OBJECTIVES

To describe the relationship between GFR, SDMA, and serum creatinine in a population of client-owned dogs, and to compare clinical utility of SDMA to GFR estimation for detecting pre-azotemic chronic kidney disease.

ANIMALS

Medical records of 119 dogs that had GFR estimation performed via serum iohexol clearance between 2012 and 2017.

METHODS

Prospective study using archived samples. GFR, SDMA, and serum creatinine results were reviewed and submitting practices contacted for outcome data. All dogs included in the study population were non-azotemic. Correlations between GFR, SDMA, and serum creatinine were determined by regression analysis. Sensitivity, specificity, and positive and negative likelihood ratios of different cutoffs for SDMA and serum creatinine for detecting decreased GFR were calculated, using a 95% confidence interval.

RESULTS

Serum creatinine and SDMA were moderately correlated with GFR (R² = 0.52 and 0.27, respectively, P < .0001) and with each other (R² = 0.33, P < .0001). SDMA >14 μg/dL was sensitive (90%) but nonspecific (50%) for detecting a ≥40% decrease in GFR. Optimal SDMA concentration cutoff for detecting a ≥40% GFR decrease was >18 μg/dL (sensitivity 90%, specificity 83%).

CONCLUSIONS AND CLINICAL IMPORTANCE

In non-azotemic dogs being screened for decreased renal function, using a cutoff of >18 μg/dL rather than >14 μg/dL increases the specificity of SDMA, without compromising sensitivity.

A possible solution to model nonlinearity in elimination and distributional clearances with α2 -adrenergic receptor agonists: Example of the intravenous detomidine and methadone combination in sedated horses

The alpha(α)₂ -agonist detomidine is used for equine sedation with opioids such as methadone. We retrieved the data from two randomized, crossover studies where detomidine and methadone were given intravenously alone or combined as boli (STUDY 1) (Gozalo-Marcilla et al., 2017, Veterinary Anaesthesia and Analgesia, 2017, 44, 1116) or as 2-hr constant rate infusions (STUDY 2) (Gozalo-Marcilla et al., 2019, Equine Veterinary Journal, 51, 530). Plasma drug concentrations were measured with a validated tandem Mass Spectrometry assay. We used nonlinear mixed effect modelling and took pharmacokinetic (PK) data from both studies to fit simultaneously both drugs and explore their nonlinear kinetics. Two significant improvements over the classical mammillary two-compartment model were identified. First, the inclusion of an effect of detomidine plasma concentration on the elimination clearances (Cls) of both drugs improved the fit of detomidine (Objective Function Value [OFV]: -160) and methadone (OFV: -132) submodels. Second, a detomidine concentration-dependent reduction of distributional Cls of each drug further improved detomidine (OFV: -60) and methadone (OFV: -52) submodel fits. Using the PK data from both studies (a) helped exploring hypotheses on the nonlinearity of the elimination and distributional Cls and (b) allowed inclusion of dynamic effects of detomidine plasma concentration in the model which are compatible with the pharmacology of detomidine (vasoconstriction and reduction in cardiac output).

Clinical utility of estimation of glomerular filtration rate in dogs

Background

Glomerular filtration rate (GFR) estimation is the gold standard for assessment of renal function, although the clinical utility of this test is unclear.

Objectives

To describe the clinical utility of GFR estimation in dogs.

Animals

Medical records of 132 dogs that had serum iohexol clearance measured between 2012 and 2017.

Methods

Iohexol clearance and clinical records were reviewed and submitting practices contacted to obtain outcome data. Dogs were classified into 4 groups based on the reason for performing GFR estimation: A1 (screening for pre‐azotemic chronic kidney disease [CKD], n = 105), A2 (confirmation of azotemic CKD, n = 3), B (screening for pre‐azotemic acute kidney injury, n = 19), and C (miscellaneous causes, n = 5). Descriptive review of the clinical utility of GFR estimation is provided.

Results

For dogs in Group A1, renal disease was diagnosed in 9/9 dogs with a GFR ≥40% decreased below the mean GFR of their body weight category, in 5/6 dogs with a ≥30% but <40% reduction in GFR and in 7/9 dogs with a ≥20% but <30% reduction in GFR.

Conclusions and Clinical Importance

Glomerular filtration rate estimation is useful for the diagnosis of CKD before the onset of azotemia.

VetCAST Method for Determination of the Pharmacokinetic-Pharmacodynamic Cut-Off Values of a Long-Acting Formulation of Florfenicol to Support Clinical Breakpoints for Florfenicol Antimicrobial Susceptibility Testing in Cattle

The PK/PD cut-off (PK/PDCO) value of florfenicol for calf pathogens was determined for long acting formulations (MSD Nuflor® and a bioequivalent generic product). PK/PDCO is one of the three MICs considered by VetCAST, a sub-committee of the European Committee on Susceptibility Testing (EUCAST), to establish a Clinical Breakpoint for interpreting Antimicrobial Susceptibility Testing (AST). A population model was built by pooling three pharmacokinetic data sets, obtained from 50 richly sampled calves, receiving one of two formulations (the pioneer product and a generic formulation). A virtual population of 5,000 florfenicol disposition curves was generated by Monte Carlo Simulations (MCS) over the 96 h of the assumed duration of action of the formulations. From this population, the maximum predicted MIC, for which 90% of calves can achieve some a priori selected critical value for two PK/PD indices, AUC/MIC and T>MIC, was established. Numerical values were established for two bacterial species of the bovine respiratory disease (BRD) complex, Pasteurella multocida and Mannheimia haemolytica. It was concluded that the PK/PDCO of florfenicol for both AUC/MIC and T>MIC was 1 mg/L.

Semi-Mechanistic Modeling of Florfenicol Time-Kill Curves and in silico Dose Fractionation for Calf Respiratory Pathogens

An important application of time-kill curve (TKC) assays is determination of the nature of the best PK/PD index (fAUC/MIC or fT% > MIC) and its target value for predicting clinical efficacy in vivo. VetCAST (the veterinary subcommittee of EUCAST) herein presents semi-mechanistic TKC modeling for florfenicol, a long acting (96 h) veterinary antimicrobial drug licensed against calf pneumonia organisms (Pasteurella multocida and Mannheimia haemolytica) to support justification of its PK/PDbreakpoint and clinical breakpoint. Individual TKC assays were performed with 6 field strains of each pathogen (initial inoculum 107 CFU/mL with sampling at times at 0, 1, 2, 4, 8, and 24 h). Semi-mechanistic modeling (Phoenix NLME) allowed precise estimation of bacteria growth system (KGROWTH, natural growth rate; KDEATH, death rate; BMAX, maximum possible culture size) and florfenicol pharmacodynamic parameters (EMAX, efficacy additive to KDEATH; EC50, potency; Gamma, sensitivity). PK/PD simulations (using the present TKC model and parameters of a florfenicol population pharmacokinetic model) predicted the time-course of bacterial counts under different exposures. Of two licensed dosage regimens, 40 mg/kg administered once was predicted to be superior to 20 mg/kg administered at 48 h intervals. Furthermore, we performed in silico dose fractionation with doses 0 - 80 mg/kg administered in 1, 2 or 4 administrations over 96 h and for MICs of 0.5, 1, 2, 4 mg/L with 2 inoculum sizes 105 and 107 CFU/mL. Regression analysis (Imax model) demonstrated that i) fAUC/MIC outperformed fT% > MIC as PK/PD index and ii) maximum efficacy (IC90%) was obtained when the average free plasma concentration over 96 h was equal to 1.2 to 1.4 times the MIC of Pasteurella multocida and Mannheimia haemolytica, respectively.

Systemic glucocorticoid usage in dogs under primary veterinary care in the UK: prevalence and risk factors

Glucocorticoids are widely used in primary care veterinary practices. The study aimed to quantify the usage of systemic glucocorticoids (SGC) in dogs in the UK using primary care treatment records recorded during 2013 in the VetCompass Programme. From a study population of 455 557 dogs, 28 472 dogs (6.2 per cent, 95 per cent CI 6.2 to 6.3) received a total of 50 971 SGC therapy events in 2013. Prednisolone represented the most frequently used oral preparation (27 362 events, 90.0 per cent of oral events). Dexamethasone sodium phosphate was the most commonly used injectable agent (12 796 events, 62.7 per cent of injectable events). The most common breed treated was Staffordshire Bull Terriers (2236/28 472 dogs, 7.9 per cent, 95 per cent CI 7.5 to 8.2) and within-breed prevalence of SGC usage was 2236/32 635, 6.9 per cent, 95 per cent CI 6.6 to 7.1. The most commonly treated age group was dogs older than eight years (8931/28472, 31.4 per cent) and the most commonly treated bodyweight group was 10.01-20.0 kg (7918/28 472, 27.8 per cent). Dexamethasone and prednisolone were the most commonly prescribed SGC. Short-acting and intermediate-acting injectable SGC were more commonly used compared with long-acting injectable SGC. Older and medium size dogs were most likely to receive SGC and certain breeds appeared predisposed. These data can provide a useful benchmark for glucocorticoid usage and highlight the benefits from 'Big Data' analyses.

Sedative and antinociceptive effects of different detomidine constant rate infusions, with or without methadone in standing horses

BACKGROUND

Standing surgery avoids the risks of general anaesthesia in horses.

OBJECTIVES

To assess sedation, antinociception and gastrointestinal motility in standing horses after a detomidine loading dose and 2-h constant rate intravenous (i.v.) infusion, with or without methadone.

STUDY DESIGN

Blinded, randomised, crossover with seven healthy adult cross-bred horses, three geldings and four females (404 ± 22 kg).

METHODS

Five i.v. treatments were administered to all horses with 1-week washout period: saline (SAL), detomidine low (2.5 μg/kg bwt + 6.25 μg/kg bwt/h) (DL) and high doses (5 μg/kg bwt + 12.5 μg/kg bwt/h) (DH) alone or combined with methadone (0.2 mg/kg bwt + 0.05 mg/kg bwt/h), (DLM) and (DHM), respectively. Height of head above the ground (HHAG), electrical (ET), thermal (TT) and mechanical (MT) nociceptive thresholds and gastrointestinal motility were evaluated at predetermined times between 5 and 240 min. A mixed effect model and Kruskal-Wallis test were used to analyse normally and non-normally distributed data, respectively.

RESULTS

Sedation (<50% basal HHAG) was achieved for the duration of the infusion, and for an additional 15 min in DH and DHM groups. Nociceptive thresholds were higher than baseline, to the greatest degree and the longest duration, with DHM (ET and TT for 135 min and MT for 150 min). After DH, TT was significantly higher than baseline from 30 to 120 min and MT from 15 to 135 min. After DLM, ET was increased at 90 min, TT at 30 min and MT for 120 min. Gastrointestinal motility was reduced for up to 135 min after DL, 150 min after DLM and 210 min after DH and DHM.

MAIN LIMITATIONS

Nociceptive thresholds are not equivalent to surgical stimuli.

CONCLUSION

Methadone with the highest detomidine dose (DHM) may provide sufficient sedation and analgesia for standing surgical procedures and warrants further investigation.

Characterisation of the in vivo interactions between detomidine and methadone in horses: Pharmacokinetic and pharmacodynamic modelling

BACKGROUND

Pharmacokinetic (PK)/pharmacodynamic (PD) modelling offers new insights to design protocols for sedation and analgesia in standing horses.

OBJECTIVES

To evaluate the parameters and interactions between detomidine and methadone when given alone or combined in standing horses.

STUDY DESIGN

Randomised, placebo-controlled, blinded, crossover.

METHODS

Eight adult healthy horses were given six treatments intravenously: saline (SAL); detomidine (5 μg/kg bwt; DET); methadone (0.2 mg/kg bwt; MET) alone or combined with detomidine (2.5 [MLD], 5 [MMD] or 10 [MHD] μg/kg bwt). Venous blood samples were obtained at predetermined times between 0 and 360 min after drug administration. Plasma detomidine and methadone were measured using a single, liquid/liquid extraction technique by liquid chromatography coupled with a triple quadrupole mass spectrometer (LC-MS/MS). Sequential PK/PD modelling compared rival models, with and without PK and PD interaction between drugs, to fit the PD data including height of the head above the ground (HHAG), a visual analogue scale for sedation (VAS), electrical (ET), thermal (TT) and mechanical (MT) nociceptive thresholds and gastrointestinal motility (GIM) [1].

RESULTS

Two and three compartment models best described the PK of detomidine and methadone, respectively. Detomidine decreased its own clearance as well as the clearance of methadone. The interaction of methadone on the effect of detomidine revealed an infra-additive (partial antagonism) effect for HHAG (α = -1.33), VAS (α = -0.98) and GIM (α = -1.05), a positive potentiation for ET (pot = 0.0041) and TT (pot = 0.133) and a synergistic to additive effect for MT (α = 0.78).

MAIN LIMITATIONS

This is a small experimental study.

CONCLUSIONS

Different PK/PD interactions were demonstrated for each PD parameter and could be modelled in vivo. The modelling of our data will allow us to simulate and predict the effect of constant rate infusions of both drugs for future investigations.

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.

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

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

Mathematical modeling and simulation in animal health. Part III: Using nonlinear mixed-effects to characterize and quantify variability in drug pharmacokinetics

A common feature of human and veterinary pharmacokinetics is the importance of identifying and quantifying the key determinants of between-patient variability in drug disposition and effects. Some of these attributes are already well known to the field of human pharmacology such as bodyweight, age, or sex, while others are more specific to veterinary medicine, such as species, breed, and social behavior. Identification of these attributes has the potential to allow a better and more tailored use of therapeutic drugs both in companion and food-producing animals. Nonlinear mixed effects (NLME) have been purposely designed to characterize the sources of variability in drug disposition and response. The NLME approach can be used to explore the impact of population-associated variables on the relationship between drug administration, systemic exposure, and the levels of drug residues in tissues. The latter, while different from the method used by the US Food and Drug Administration for setting official withdrawal times (WT) can also be beneficial for estimating WT of approved animal drug products when used in an extralabel manner. Finally, NLME can also prove useful to optimize dosing schedules, or to analyze sparse data collected in situations where intensive blood collection is technically challenging, as in small animal species presenting limited blood volume such as poultry and fish.

Factors Influencing the Relationship Between the Dose of Amlodipine Required for Blood Pressure Control and Change in Blood Pressure in Hypertensive Cats

Background

Hypertension is a common problem in elderly cats. In most cats, systolic blood pressure (SBP) of <160 mmHg is achieved in response to amlodipine besylate at either 0.625 or 1.25 mg q24h. The individual cat factors determining dose requirement dose have not been explored.

Aims

To determine whether individual cat factors influence the dose of amlodipine required to achieve adequate blood pressure control and to determine whether factors other than the prescribed dose of drug alter the achieved plasma amlodipine concentrations.

Methods

Fifty‐nine hypertensive cats that required 0.625 mg (A) and 41 cats that required 1.25 mg (B) amlodipine to reach a target SBP of <160 mmHg were identified, and plasma amlodipine concentrations were determined. Comparisons were made between groups, and multivariable linear regression models were performed to investigate predictors of antihypertensive response.

Results

Cats that required a greater dose of amlodipine had significantly higher SBP at diagnosis of hypertension (A: (median [25th, 75th percentile]) 182 [175,192] mmHg; B: 207 [194,217] mmHg, P < .001), but comparable blood pressure was achieved after treatment. Plasma amlodipine concentrations were directly related to the dose of amlodipine administered. At diagnosis, cats in group B had significantly lower plasma potassium concentration (A: 4.1 [3.8,4.5]; B: 3.8 [3.6,4.2] mEq/L, P < .01). Weight did not differ between groups. The decrease in SBP was directly and independently associated with the SBP at diagnosis and the plasma amlodipine concentration.

Conclusions and Clinical Importance

Cats with higher blood pressure at diagnosis might require a greater dose of amlodipine to control their blood pressure adequately. Differences in amlodipine pharmacokinetics between cats do not seem to play a role in the antihypertensive response.

En Route towards European Clinical Breakpoints for Veterinary Antimicrobial Susceptibility Testing: A Position Paper Explaining the VetCAST Approach

VetCAST is the EUCAST sub-committee for Veterinary Antimicrobial Susceptibility Testing. Its remit is to define clinical breakpoints (CBPs) for antimicrobial drugs (AMDs) used in veterinary medicine in Europe. This position paper outlines the procedures and reviews scientific options to solve challenges for the determination of specific CBPs for animal species, drug substances and disease conditions. VetCAST will adopt EUCAST approaches: the initial step will be data assessment; then procedures for decisions on the CBP; and finally the release of recommendations for CBP implementation. The principal challenges anticipated by VetCAST are those associated with the differing modalities of AMD administration, including mass medication, specific long-acting product formulations or local administration. Specific challenges comprise mastitis treatment in dairy cattle, the range of species and within species breed considerations and several other variable factors not relevant to human medicine. Each CBP will be based on consideration of: (i) an epidemiological cut-off value (ECOFF) - the highest MIC that defines the upper end of the wild-type MIC distribution; (ii) a PK/PD breakpoint obtained from pre-clinical pharmacokinetic data [this PK/PD break-point is the highest possible MIC for which a given percentage of animals in the target population achieves a critical value for the selected PK/PD index (fAUC/MIC or fT > MIC)] and (iii) when possible, a clinical cut-off, that is the relationship between MIC and clinical cure. For the latter, VetCAST acknowledges the paucity of such data in veterinary medicine. When a CBP cannot be established, VetCAST will recommend use of ECOFF as surrogate. For decision steps, VetCAST will follow EUCAST procedures involving transparency, consensus and independence. VetCAST will ensure freely available dissemination of information, concerning standards, guidelines, ECOFF, PK/PD breakpoints, CBPs and other relevant information for AST implementation. Finally, after establishing a CBP, VetCAST will promulgate expert comments and/or recommendations associated with CBPs to facilitate their sound implementation in a clinical setting.

Evaluation of analgesic effect and absorption of buprenorphine after buccal administration in cats with oral disease

Objectives

The objective of this study was to evaluate the analgesic effect and absorption of buprenorphine after buccal administration in cats with oral disease.

Methods

Six adult client-owned cats with chronic gingivostomatitis (weighing 5.1 ± 1.1 kg) were recruited for a randomised, prospective, blinded, saline-controlled, crossover study. Pain scores, dental examination, stomatitis score and buccal pH measurement were conducted on day 1 under sedation in all cats. On day 2, animals were randomised into two groups and administered one of the two treatments buccally (group A received buprenorphine 0.02 mg/kg and group B received 0.9% saline) and vice versa on day 3. Pain scores and food consumption were measured at 30, 90 and 360 mins after the administration of buprenorphine. Blood samples were taken at the same time and plasma buprenorphine concentration was measured by liquid chromatography–mass spectrometry. Data were statistically analysed as non-parametric and the level of significance was set as P <0.05.

Results

There were no major side effects after buprenorphine administration. Buccal pH values ranged between 8.5 and 9.1 and the stomatitis disease activity index between 10 and 22 (17.8 ± 4.5), with the scale ranging from 0–30. The maximum buprenorphine plasma concentration (14.8 ng/ml) was observed 30 mins after administration and there was low inter-individual variability. There was a significant difference between baseline pain scores compared with pain scores after buprenorphine ( P <0.05), and between the saline and buprenorphine group at 30 mins ( P = 0.04) and 90 mins ( P = 0.04). There was also a significant effect of the stomatitis index on the pain score. Regarding the pharmacokinetic parameters, cats with stomatitis showed lower bioavailability and shorter absorption half-life after buccal administration of buprenorphine compared with normal cats in previous studies.

Conclusions and relevance

Buccal administration of buprenorphine in cats with gingivostomatitis produces an analgesic effect and low inter-individual variability in plasma concentration, and it can be incorporated in their multimodal analgesia plan.