Patient variation in veterinary medicine: part I. Influence of altered physiological states

Pharmacokinetics, bioavailability and plasma protein binding of tolfenamic acid in rainbow trout (Oncorhynchus mykiss)

BACKGROUND

Although research on the mechanism and control of pain and inflammation in fish has increased in recent years, the use of analgesic drugs is limited due to the lack of pharmacological information about analgesic drugs. Tolfenamic acid is a non-steroidal anti-inflammatory drug and can be used in fish due to its low side effect profile and superior pharmacokinetic properties.

OBJECTIVES

The pharmacokinetics, bioavailability and plasma protein binding of tolfenamic acid were investigated following single intravascular (IV), intramuscular (IM) and oral administration of 2 mg/kg in rainbow trout at 13 ± 0.5°C.

METHODS

The experiment was carried out on a total of 234 rainbow trout (Oncorhynchus mykiss). Tolfenamic acid was administered to fish via IV, IM and oral route at a dose of 2 mg/kg. Blood samples were taken at 13 different sampling times until the 72 h after drug administration. The plasma concentrations of tolfenamic acid were quantified using high pressure liquid chromatography-ultraviolet (UV) and pharmacokinetic parameters were assessed using non-compartmental analysis.

RESULTS

The elimination half-life (t1/2ʎz) of tolfenamic acid for IV, IM and oral routes was 3.47, 6.75 and 9.19 h, respectively. For the IV route, the volume of distribution at a steady state and total body clearance of tolfenamic acid were 0.09 L/kg and 0.03 L/h/kg, respectively. The peak plasma concentration and bioavailability for IM and oral administration were 8.82 and 1.24 µg/mL, and 78.45% and 21.48%, respectively. The mean plasma protein binding ratio of tolfenamic acid in rainbow trout was 99.48% and was not concentration dependent.

CONCLUSIONS

While IM route, which exhibits both the high plasma concentration and bioavailability, can be used in rainbow trout, oral route is not recommended due to low plasma concentration and bioavailability. However, there is a need to demonstrate the pharmacodynamic activity of tolfenamic acid in rainbow trout.

Efficacy of eprinomectin 5 mg/mL topical solution administered pour on at 1 mg per kg body weight against Oestrus ovis myiasis in sheep and goats

The larvae of the nasal bot, Oestrus ovis, mainly parasitize sheep and goats and some species of wild Caprinae but other mammals and humans are also vulnerable to infestation. Eprinomectin 5 mg/mL topical solution (EPRINEX® Multi, Boehringer Ingelheim) administered at 1 mg eprinomectin per kg body weight pour on was recently authorized as an anthelmintic for sheep and goats with zero hours milk withdrawal in several countries in Europe. As the product in cattle has claims against a broad range of parasites including insect parasites and activity against O. ovis has previously been reported following extra-label use in sheep, its therapeutic efficacy against ovine and caprine O. ovis myiasis was evaluated in three regulatory compliant, masked clinical studies. Pre-study recovery of O. ovis larvae from five or six of six randomly selected animals per study site (Bulgaria, one site, sheep; Greece, two sites, sheep or goats) supported the inclusion of the animals from those sites into the studies. The study animals (34 animals per study) were ranked based on bodyweight and allocated randomly to remain untreated (control) or to be treated with eprinomectin 5 mg/mL topical solution at 1 mL per 5 kg body weight pour on. Treatment efficacy was determined based on O. ovis larval counts of eprinomectin 5 mg/mL topical solution-treated vs. untreated animals three weeks after treatment administration. Live O. ovis larvae, including all three instars in each study, were recovered from 13 or 16 of the 17 control animals in the sheep studies (range, 1 to 14 or 5 to 18 larvae, respectively) and from all 17 controls in the goat study (range, 7 to 18 larvae). In each study, eprinomectin 5 mg/mL topical solution-treated animals had significantly (p < 0.001) fewer live O. ovis larvae than the controls. Efficacy of the treatment was 100% and 91.3% against the combined parasitic O. ovis larval stages in sheep and in goats, respectively. The treatment was well accepted by all animals and no health problems were observed throughout the studies. The results of these studies demonstrated eprinomectin 5 mg/mL topical solution administered pour on at 1 mL per 5 kg body weight to be an efficacious and safe treatment of ovine and caprine oestrosis.

Pharmacokinetics of meloxicam in pre-ruminant calves after intravenous, oral, and subcutaneous administration

Meloxicam is routinely used for pain alleviation in pre-ruminant calves during husbandry procedures. The pharmacokinetics of a single dose (0.5 mg/kg) of meloxicam was investigated after intravenous (IV), subcutaneous (SC), and oral (PO) administration in 30 pre-ruminant calves. Each group included 10 calves. Oral meloxicam was administered at least 1 h after feeding. Plasma samples were collected for up to 168 h, and the meloxicam concentration was analysed with liquid chromatography and mass spectrometry, followed by a noncompartmental pharmacokinetic analysis. The maximum meloxicam concentrations in plasma were 1.91 ± 0.27 μg/mL and 1.77 ± 0.16 μg/mL after SC and PO routes, respectively. The time of maximum concentration was 7.6 ± 2.8 h after SC and 10.0 ± 5.7 h after PO administration. The approximate bioavailability of meloxicam was 97% for SC and PO routes. The elimination half-lives were 79.2 ± 12.4, 84.6 ± 24.8, and 84.8 ± 22.3 h after IV, SC, and PO routes, respectively. The results suggest that the therapeutic meloxicam concentrations in plasma that are required for pain relief in other species, such as horses, may be maintained for several days following a single dose (0.5 mg/kg) administered IV, SC, or PO in calves.

Linalool, 1,8-Cineole, and Eugenol Transfer from a Curry Dish into Human Urine

SCOPE

For most substances, there are several routes of excretion from the human body. This study focuses on urinary excretion of dietary odorants and compares the results with previously obtained results on excretion into milk.

METHODS AND RESULTS

Lactating mothers (n = 18) are given a standardized curry dish and donate urine samples before and after the intervention. The odorants 1,8-cineole, linalool, cuminaldehyde, cinnamaldehyde, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, sotolone, eugenol, vanillin, and γ-nonalactone are quantitatively analyzed. A significant transition of up to 6 µg g-1 creatinine into urine is observed for linalool, 1,8-cineole, and eugenol. Maximum concentrations are reached 1.5 h after the intervention for 1,8-cineole and eugenol as well as 2.5 h after the intervention for linalool. Comparison with previous results reveals that the excretion pattern of odorants into urine is divergent from the one into milk. In a second intervention study (n = 6), excretion of phase II metabolites into urine is studied using β-glucuronidase treatment. Linalool and eugenol concentrations are 23 and 77 times higher after treatment than before treatment with β-glucuronidase, respectively.

CONCLUSION

The study demonstrates transition of linalool, 1,8-cineole, and eugenol from the diet into urine and excretion of glucuronides in the case of linalool, eugenol, and vanillin.

First Investigation of the Physiological Distribution of Legacy and Emerging Perfluoroalkyl Substances in Raw Bovine Milk According to the Component Fraction

Bovine milk is a pillar of the human diet and plays a key role in the nutrition of infants. Perfluoroalkyl substances (PFASs) are well-recognized highly stable organic compounds that are able to pollute ecosystems persistently and threaten both human and animal health. The study aimed to analyze the distribution of 14 PFASs within the milk matrix by comparing their content in whole milk, and its skimmed and creamed fractions. Raw milk samples were individually collected from 23 healthy cows (10 primiparous and 13 multiparous) reared on a farm in Northern Italy not surrounded by known point sources of PFASs. Each sample was fractioned in whole, skim, and cream components to undergo PFAS analysis using liquid chromatography-high-resolution mass spectrometry. All samples contained at least one PFAS, with perfluorobutanoic acid (PFBA) being the primary contaminant in all three fractions, followed by perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA). PFOS was shown to be significantly (p < 0.001) more concentrated in cream than in raw and skimmed milk. Multiparous cows showed a higher frequency of positive samples in all analyzed fractions. Further research is necessary to assess the risk of dairy diets and high-fat dairy products and to investigate the toxicological effects of PFASs on cattle, even in environments without known PFAS sources.

Effects of a single transdermal administration of flunixin meglumine in early postpartum Holstein Friesian dairy cows: Part 1. Inflammatory and metabolic markers, uterine health, and indicators of pain

The objectives of this study were to assess the effects of a single transdermal administration of flunixin meglumine (FM) in early postpartum Holstein Friesian dairy cows on serum concentrations of inflammatory and metabolic markers, uterine health, and indicators of pain. The hypothesis was that the anti-inflammatory, antipyretic, and analgetic effects of the pharmaceutic agent would reduce systemic inflammation, resulting in improved metabolic and inflammatory profile, diminished incidence of metritis, and reduced expression of pain. A total of 500 cows (153 primiparous, 347 multiparous) from 3 different commercial dairy farms in the northeast of Germany were included in a randomized controlled clinical trial. Farms were preselected based on high haptoglobin concentrations in their fresh lactating cows. Cows were excluded if they had experienced dystocia, stillbirth, or twin birth, or if they showed any signs of milk fever, retained fetal membranes, or fever (>40°C). The cows were treated once with either FM (3.33 mg/kg) or a placebo as control (CON) through transdermal administration between 24 to 36 h postpartum (d 2). General health examinations were performed (daily from d 2-8 and additionally on d 15 postpartum), vaginal discharge was assessed using the Metricheck device (d 8 and 15 postpartum) and serum samples were analyzed for inflammatory and metabolic markers (d 2, 4, and 6 postpartum). Effects of treatment, parity, sampling day, and their interactions were evaluated using mixed effects models. Primiparous cows treated with FM showed lower serum haptoglobin concentrations (0.90 ± 0.08 vs. 1.17 ± 0.07 g/L; ± standard error of the mean) and higher serum albumin concentrations (35.5 ± 0.31 vs. 34.8 ± 0.31 g/L) on d 6 postpartum. They also had a lower risk for purulent vaginal discharge with or without a fever compared with CON cows on d 15 postpartum (odds ratio for CON vs. FM: 1.63, 95% CI: 1.26-2.00), and body temperature was lower throughout the first 15 d in milk (39.1 ± 0.11 vs. 39.2 ± 0.11°C). Multiparous cows treated with FM had lower serum β-hydroxybutyrate concentrations on d 4 postpartum (0.71 ± 0.05 vs. 0.78 ± 0.05 mmol/L) and d 6 postpartum (0.74 ± 0.05 vs. 0.80 ± 0.05 mmol/L). Regardless of parity, FM-treated cows were significantly less likely to abduct their tail from their body (14.3 vs. 23.6%) and show an arched back (27.9 vs. 39.7%) on the day after treatment compared with CON cows. It can be concluded that FM treatment slightly reduced inflammation and diminished the risk for metritis in primiparous cows, improved metabolic profile in multiparous cows, and reduced expressions of pain in all cows.

Pharmacokinetics and bioavailability of meloxicam in rainbow trout (Oncorhynchus mykiss) broodstock following intravascular, intramuscular, and oral administrations

The pharmacokinetics and bioavailability of meloxicam were investigated after single intravascular (IV), intramuscular (IM), and oral dose of 1 mg/kg in rainbow trout broodstock at 11 ± 1.2°C. A total of 36 healthy rainbow trout (Oncorhynchus mykiss) broodstock weighing 1.40 ± 0.26 kg was used for the investigation. Plasma concentrations of meloxicam were measured with high-performance liquid chromatography-ultraviolet detection, and pharmacokinetic parameters were calculated by non-compartmental analysis. The elimination half-life for IV, IM, and oral routes was 3.63, 4.55, and 2.95 h, respectively. The IV route for meloxicam showed the total clearance of 0.05 L/h/kg and volume of distribution at a steady state of 0.20 L/kg. The peak plasma concentration was 2.97 μg/ml for the IM route and 0.84 μg/ml for the oral route. The bioavailability was 78.45% for the IM route and 21.48% for the oral route. Meloxicam following IM and oral administration displayed short t_1/2ʎz . The short t_1/2ʎz could be an advantage for the short-term use in acute conditions. The IM route with the good bioavailability can be preferred for the treatment of various conditions. However, developing new oral formulations with the good bioavailability for meloxicam is necessary to minimize stress and trauma through minimal handling in rainbow trout broodstock.

Pharmacokinetic Behavior and Pharmacokinetic/Pharmacodynamic Integration of Danofloxacin Following Single or Co-Administration with Meloxicam in Healthy Lambs and Lambs with Respiratory Infections

The aim of this study was to determine the pharmacokinetics and pharmacodynamics of danofloxacin (DAN; 6 mg/kg) following subcutaneous administration alone or co-administration with meloxicam (MLX; 1 mg/kg) in healthy lambs and lambs with respiratory infections. The study was carried out using a total of four groups: HD (healthy; n = 6) and ID (infected; n = 7) groups who were administered DAN only, and HDM (healthy; n = 6) and IDM (infected; n = 7) groups who were administered DAN and MLX simultaneously. The plasma concentrations of DAN were determined using high-performance liquid chromatography–UV and analyzed by the non-compartmental method. DAN exhibited a similar elimination half-life in all groups, including both the healthy and infected lambs. The total clearance in the HDM, ID and IDM groups and volume of distribution in the HDM and IDM groups were significantly reduced. MLX in the IDM group significantly increased the area under the curve (AUC) and peak concentration (C_max) of DAN compared to the HD group. The Mannheimia haemolytica, Escherichia coli, and Streptococcus spp. strains were isolated from bronchoalveolar lavage fluid samples of the infected lambs. When co-administration with meloxicam, DAN at a 6 mg/kg dose can provide optimum values of ƒAUC_0–24/MIC (>56 h) and ƒC_max/MIC (>8) for susceptible M. haemolytica isolates with an MIC₉₀ value of 0.25 µg/mL and susceptible E. coli isolates with an MIC value of ≤0.125 µg/mL.

Pour-on administration of eprinomectin to lactating dairy goats: Pharmacokinetics and anthelmintic efficacy

Lactation is discussed as a physiological covariate which may influence the exposure characteristics of systemically acting drugs including macrocyclic lactones and potentially alter their pharmacological response. This study characterizes for the first time in the same study, the plasma profile and therapeutic anthelmintic efficacy of eprinomectin 5 mg/ml solution (EPRINEX^® Multi, Boehringer Ingelheim) administered as a pour-on at 1 mg per kg body weight to lactating dairy goats. The study was conducted in compliance with VICH GCP and anthelmintic efficacy evaluation guidelines and included 20 goats harboring induced adult gastrointestinal and pulmonary nematode infections. The goats were blocked on pre-treatment body weight and randomly allocated either to remain untreated (control) or to be eprinomectin-treated. Plasma samples to determine the plasma disposition kinetics of eprinomectin (B1a component) were obtained at intervals up to 14 days following treatment when the animals were necropsied for parasite enumeration and identification. Basic pharmacokinetic parameters of eprinomectin determined in the ten eprinomectin-treated goats were as follows: AUC_last , 23.8 ± 9.7 day*ng/ml and C_max , 5.35 ± 2.27 ng/ml; individual maximum plasma concentrations were observed from 8 to 48 h after treatment (median T_max , 0.5 days). Topical eprinomectin treatment efficacy, based on significant (p < .01) worm burden reductions in eprinomectin-treated animals relative to untreated controls, was ≥97% to 100% against adult Dictyocaulus filaria, Haemonchus contortus, Teladorsagia circumcincta(pinnata/trifurcata), Trichostrongylus axei, T. colubriformis, Cooperia curticei, Nematodirus battus, and Oesophagostomum venulosum. Both pharmacokinetic parameters and anthelmintic activity in lactating dairy goats were similar to those observed in parasitized young growing and adult female non-lactating dairy goats treated with eprinomectin administered as a pour-on.

Pharmacokinetics of meloxicam, carprofen, and tolfenamic acid after intramuscular and oral administration in Japanese quails (Coturnix coturnix japonica)

The aim of this study was to determine the pharmacokinetics of meloxicam (MLX), carprofen (CRP), and tolfenamic acid (TA) in Japanese quails (Coturnix coturnix japonica) following intramuscular (IM) and oral administration at doses of 1, 10, and 2 mg/kg, respectively. A total of 72 quails were randomly divided into 3 equal groups as MLX, CRP, and TA. Each group was separated into two sub-groups that received IM and oral administration of each drug. Plasma concentrations of MLX, CRP, and TA were determined using HPLC-UV and analyzed by non-compartmental method. The t_1/2ʎz and MRT of MLX, CRP, and TA after oral administration were similar to those after IM administration. The V_darea /F of MLX, CRP, and TA after IM administration was 0.28, 2.05, and 0.20 L/kg. The Cl/F of MLX, CRP, and TA after IM administration was 0.12, 0.19, and 0.09 L/h/kg. MLX, CRP, and TA after oral administration showed significantly lower C_max and longer T_max compared with IM administration. The relative bioavailability of MLX, CRP, and TA following oral administration in quails was 76.13%, 61.46%, and 57.32%, respectively. The IM and oral route of MLX, CRP, and TA can be used for the treatment of various conditions in quails. However, further research is necessary to determine the pharmacodynamics and safety of MLX, CRP, and TA before use in quails.

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.

Pharmacological considerations of antibiotic failures in bovine respiratory disease cases

Bovine respiratory disease (BRD) is one of the most common indications for antimicrobial therapy in beef cattle production and research trials demonstrate that antibiotic therapy greatly improves clinical outcome for BRD. These trials also show that BRD treatment success rates are less than 100% and that there are opportunities to optimize antimicrobial prescribing and improve clinical outcomes if the underlying cause(s) of BRD treatment failures can be identified and addressed. As the etiology of BRD in an individual animal is frequently multi-factorial in nature; it is likely that BRD treatment failures also result from complex interactions between the drug, drug administrator, animal host, pathogens, and the environment. This review will focus specifically on the pharmacological aspects, specifically the interactions between the host and the drug and the drug and the drug administrator, of BRD treatment failures and the actions that veterinary practitioners can take to investigate and mitigate therapeutic failures in future cases.

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.

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.

A Defined and Scalable Peptide-Based Platform for the Generation of Human Pluripotent Stem Cell-Derived Astrocytes

Astrocytes comprise the most abundant cell type in the central nervous system (CNS) and play critical roles in maintaining neural tissue homeostasis. In addition, astrocyte dysfunction and death has been implicated in numerous neurological disorders such as multiple sclerosis, Alzheimer’s disease, amyotrophic lateral sclerosis (ALS), and Parkinson’s disease (PD). As such, there is much interest in using human pluripotent stem cell (hPSC)-derived astrocytes for drug screening, disease modeling, and regenerative medicine applications. However, current protocols for generation of astrocytes from hPSCs are limited by the use of undefined xenogeneic components and two-dimensional (2D) culture surfaces, which limits their downstream applications where large-quantities of cells generated under defined conditions are required. Here, we report the use of a completely synthetic, peptide-based substrate that allows for the differentiation of highly pure populations of astrocytes from several independent hPSC lines, including those derived from patients with neurodegenerative disease. This substrate, which we demonstrate is compatible with both conventional 2D culture formats and scalable microcarrier (MC)-based technologies, leads to the generation of cells that express high levels of canonical astrocytic markers as well as display properties characteristic of functionally mature cells including production of apolipoprotein E (ApoE), responsiveness to inflammatory stimuli, ability to take up amyloid-β (Aβ), and appearance of robust calcium transients. Finally, we show that these astrocytes can be cryopreserved without any loss of functionality. In the future, we anticipate that these methods will enable the development of bioprocesses for the production of hPSC-derived astrocytes needed for biomedical research and clinical applications.

Impact of lactation on pharmacokinetics of meloxicam in goats

Use of drug in lactating animal should be carefully considered due to its possibility of changes in pharmacokinetics as well as drug penetration in milk. The aim of this study was to assess the effect of lactation on pharmacokinetics of meloxicam after IV and IM administrations in goats. A crossover design (2 × 2) was used for each lactating and nonlactating group of goats with a 3-week washout period. Meloxicam (0.5 mg/kg) was administered into the jugular vein and upper gluteal muscle by IV and IM routes, respectively. The plasma and milk drug concentrations were determined by high-performance liquid chromatography with diode array detector, and the pharmacokinetic analysis was carried out by noncompartmental analysis. The pharmacokinetic parameters of meloxicam in lactating and nonlactating goats were not significantly different. The IM bioavailability of meloxicam was relatively lower in lactating (75.3 ± 18.6%) than nonlactating goats (103.8 ± 34.7%); however, the difference was not statistically significant. Moreover, AUC ratio between milk and plasma, which represent drug milk penetration, for both IV and IM administrations was less than 1 (about 0.3). In conclusion, pharmacokinetic parameters of meloxicam are not significantly altered by lactation for either the IV or IM routes of administration and this drug does not require a different dosage regimen for lactating animals.

Impact of bovine respiratory disease on the pharmacokinetics of danofloxacin and tulathromycin in different ages of calves

Pneumonia is one of the most economically important respiratory diseases of calves and knowledge of the impact of clinical disease on pharmacokinetics (PK) in young calves is limited. This study was undertaken to investigate the efficacy and PK of two antibiotics, tulathromycin and danofloxacin, in two age groups of calves experimentally infected with Pasteurella multocida. Both danofloxacin, a fluoroquinolone antibiotic, and tulathromycin, a macrolide antibiotic is approved for the treatment of bovine respiratory disease (BRD). To evaluate potential influences of age and disease on drug distribution and elimination in calves, plasma, interstitial fluid (ISF), and pulmonary epithelial lining fluid (PELF) were analyzed for drug concentrations. Concentrations for both drugs in the PELF were estimated by a urea dilution assay of the collected bronchoalveolar lavage fluids. Age was determined to be a significant covariate for calves administered danofloxacin and tulathromycin for plasma PK parameters. For calves administered danofloxacin, the area under the curve (AUC) in the plasma was lower in 6-month old calves (18.9 ± 12.6 hr* μg/mL) vs. 3-week old calves (32.0 ± 8.2 hr* μg/mL). Clearance (CL/F) of danofloxacin was higher in 6-month old calves. In contrast, tulathromycin plasma concentrations were higher in 6 month old calves and CL/F was higher in 3-week old calves. Age did not significantly influence the ISF concentrations of danofloxacin or tulathromycin in calves with respiratory disease, unlike previous studies which reported higher ISF concentrations of danofloxacin and tulathromycin in 6-month old calves when compared to younger calves. PELF concentrations were higher than plasma and ISF for both danofloxacin and tulathromycin, but did not differ between age groups. Potential reasons for age-related differences on plasma concentration–time profiles and the impact of disease on the partitioning of the drug from the blood to the lungs and ISF as a function of age are explored.

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.

Pharmacokinetics of ceftiofur in healthy and lipopolysaccharide-induced endotoxemic newborn calves treated with single and combined therapy

The aim of this research was to compare plasma pharmacokinetics of ceftiofur sodium (CS) in healthy calves, and in calves with experimentally induced endotoxemia. Six calves received CS (2.2 mg/kg, IM) 2 hr after intravenous administration of 0.9% NaCl (Ceft group). After a washout period, the same 6 calves received CS 2 hr after intravenous injection of lipopolysaccharide (LPS+Ceft group). Another group of 6 calves received a combination of drug therapies that included CS 2 hr after administration of 0.9% NaCl (Comb group). A third group of 6 calves received the same combination therapy regimen 2 hr after intravenous injection of lipopolysaccharide (LPS+Comb group). Plasma concentrations of CS and all desfuroylceftiofur-related metabolites were determined using HPLC, and its pharmacokinetic properties were determined based on a two-compartment model. The peak concentration of CS in the LPS+Comb group occurred the earliest, and the clearance rate of CS was the highest in the Comb and LPS+Comb groups (P<0.05). The elimination half-life of CS in the LPS+Ceft group was longer than that in the Ceft and Comb groups (P<0.05). The results of this study indicate that combined therapies and endotoxemic status may alter the plasma pharmacokinetics of CS in calves.

Comparison of pharmacokinetics and milk elimination of flunixin in healthy cows and cows with mastitis

OBJECTIVE

To determine whether pharmacokinetics and milk elimination of flunixin and 5-hydroxy flunixin differed between healthy and mastitic cows.

DESIGN

Prospective controlled clinical trial.

ANIMALS

20 lactating Holstein cows.

PROCEDURES

Cows with mastitis and matched control cows received flunixin IV, ceftiofur IM, and cephapirin or ceftiofur, intramammary. Blood samples were collected before (time 0) and 0.25, 0.5, 1, 2, 4, 8, 12, 24, and 36 hours after flunixin administration. Composite milk samples were collected at 0, 2, 12, 24, 36, 48, 60, 72, 84, and 96 hours. Plasma and milk samples were analyzed by use of ultra-high-performance liquid chromatography with mass spectrometric detection.

RESULTS

For flunixin in plasma samples, differences in area under the concentration-time curve and clearance were detected between groups. Differences in flunixin and 5-hydroxy flunixin concentrations in milk were detected at various time points. At 36 hours after flunixin administration (milk withdrawal time), 8 cows with mastitis had 5-hydroxy flunixin concentrations higher than the tolerance limit (ie, residues). Flunixin residues persisted in milk up to 60 hours after administration in 3 of 10 mastitic cows.

CONCLUSIONS AND CLINICAL RELEVANCE

Pharmacokinetics and elimination of flunixin and 5-hydroxy flunixin in milk differed between mastitic and healthy cows, resulting in violative residues. This may partially explain the high number of flunixin residues reported in beef and dairy cattle. This study also raised questions as to whether healthy animals should be used when determining withdrawal times for meat and milk.

Metronidazole pharmacokinetics during rapid growth in turkeys - relation to changes in haemodynamics and drug metabolism

Whereas interspecies variation in pharmacokinetics is a commonly investigated issue, variations in drug kinetics within a species are less documented. The aim of the study was to assess the influence of age-related changes in haemodynamics on the pharmacokinetics of metronidazole (MTZ) and its hydroxy metabolite (MTZ-OH) in turkeys. MTZ was administered intravenously and orally at a dose of 25 mg/kg. Plasma drug and metabolite concentrations were assessed by high-performance liquid chromatography, and pharmacokinetic parameters were calculated by noncompartmental analysis. Haemodynamic parameters (heart rate, stroke volume, cardiac output) were assessed by echocardiography and extraction ratio for MTZ was calculated based on total body clearance (ClB ). Between the 5th and 15th week of age, ClB of MTZ decreased from 3.6 to 1.2 mL/min/kg causing a twofold increase in the mean residence time (MRT) and elimination half-life (T1/2el ). The MTZ-OH production decreased threefold and its MRT and T1/2el increased. Although heart rate significantly decreased with age, cardiac output increased. Extraction ratio was low in all age groups. It is concluded that significant age-dependent decrease in ClB of MTZ in turkeys resulted from decreased perfusion of the clearing organs and their reduced metabolic capacity. This phenomenon is probably species specific and may apply to other therapeutic agents.

Disposition of cimicoxib in plasma and milk of whelping bitches and in their puppies

BACKGROUND

Caesarean section of bitches is a well recognized painful condition in dogs and it can be classified as a soft tissue surgery. Cimicoxib, a newly registered NSAID in European Union has a claim for the relief of pain in peri-operative conditions. However, in case of caesarean section, the main concerns of using NSAIDs are the transfer of the drugs into milk and its impact on the suckling pups. Thus, the aim of the present work was to evaluate the transfer of cimicoxib into the milk of 6 lactating bitches after a single oral administration of the drug on day 0 (just after whelping) and on day 28 at the target dose of 2 mg/kg. Another aim of the study was to evaluate the transfer of the drug from the milk into the suckling pups. Blood and milk samples were collected from the bitches after each administration on day 0 and day 28 and blood samples were drawn from the pups after suckling on day 28.

RESULTS

All bitches whelped without any complication and gave birth to 38 pups. After administration on D0, the mean observed plasma Cmax in bitches was 0.5323 μg/mL and the mean area under the concentration-time curve extrapolated to the infinity, AUCINF, was 2.411 μg.h/mL. After administration on D28, only AUCINF was significantly higher with a value of 3.747 μg.h/mL. In milk, after administration on D0, the mean observed Cmax was 0.9974 μg/mL and the mean area under the concentration-time curve until the last measurable time point, AUClast, was 4.205 μg.h/mL. Out of 24 sampled pups on D28, only 2 animals had a sample with very low cimicoxib concentrations slightly above the limit of quantification (0.01 μg/mL).

CONCLUSION

The presented data show that cimicoxib given by oral route to lactating bitches at a single dose of 2 mg/kg had a high transfer rate into the milk with a milk to plasma ratio of 1.7 to 1.9. The transfer rate to the suckling pups was low and no clinical abnormalities were detected in both bitches and pups.

Use of Monte Carlo simulation to determine pharmacodynamic cutoffs of amoxicillin to establish a breakpoint for antimicrobial susceptibility testing in pigs

OBJECTIVE

To determine pharmacodynamic cutoffs with pharmacokinetic-pharmacodynamic principles and Monte Carlo simulation (MCS) for use of amoxicillin in pigs to set interpretive criteria for antimicrobial susceptibility testing.

SAMPLE

191 plasma disposition curves of amoxicillin obtained from 21 IV, 104 IM, and 66 PO administrations corresponding to 2,098 plasma concentrations.

PROCEDURES

A population model of amoxicillin disposition in pigs was developed for PO and IM administration. The MCS method was then used to determine, for various dosage regimens, the proportion of pigs achieving plasma amoxicillin concentrations greater than a selection of possible minimal inhibitory concentrations (MICs) ranging from 0.0625 to 4 mg/L for at least 40% of a 24-hour period.

RESULTS

A target attainment rate (TAR) of 90% was never achieved with the breakpoint recommended by the Clinical and Laboratory Standards Institute (0.5 mg/L) when the usual recommended dosage (20 mg/kg/d) was used. Only by dividing the orally administered daily dose into 12-hour administration intervals was a TAR > 90% achieved when the total dose was at least 40 mg/kg for a pathogen having an MIC ≤ 0.0625 mg/L. For the IM route, the TAR of 90% could only be achieved for MICs of 0.0625 and 0.125 mg/L with the use of 15 and 30 mg/kg doses, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Population kinetics and MCS are required to determine robust species-specific interpretive criteria (susceptible, intermediate, and resistant classifications) for antimicrobial susceptibility testing breakpoints (taking into account interanimal variability).

Development of a physiologically based pharmacokinetic model for flunixin in cattle (Bos taurus)

Frequent violation of flunixin residues in tissues from cattle has been attributed to non-compliance with the USFDA-approved route of administration and withdrawal time. However, the effect of administration route and physiological differences among animals on tissue depletion has not been determined. The objective of this work was to develop a physiologically based pharmacokinetic (PBPK) model to predict plasma, liver and milk concentrations of flunixin in cattle following intravenous (i.v.), intramuscular (i.m.) or subcutaneous (s.c.) administration for use as a tool to determine factors that may affect the withdrawal time. The PBPK model included blood flow-limited distribution in all tissues and elimination in the liver, kidney and milk. Regeneration of parent flunixin due to enterohepatic recirculation and hydrolysis of conjugated metabolites was incorporated in the liver compartment. Values for physiological parameters were obtained from the literature, and partition coefficients for all tissues but liver and kidney were derived empirically. Liver and kidney partition coefficients and elimination parameters were estimated for 14 pharmacokinetic studies (including five crossover studies) from the literature or government sources in which flunixin was administered i.v., i.m. or s.c. Model simulations compared well with data for the matrices following all routes of administration. Influential model parameters included those that may be age or disease-dependent, such as clearance and rate of milk production. Based on the model, route of administration would not affect the estimated days to reach the tolerance concentration (0.125 mg kg(-1)) in the liver of treated cattle. The majority of USDA-reported violative residues in liver were below the upper uncertainty predictions based on estimated parameters, which suggests the need to consider variability due to disease and age in establishing withdrawal intervals for drugs used in food animals. The model predicted that extravascular routes of administration prolonged flunixin concentrations in milk, which could result in violative milk residues in treated cattle.

Expression and subcellular localization of efflux transporter ABCG2/BCRP in important tissue barriers of lactating dairy cows, sheep and goats

Expression of efflux transporter ABCG2/BCRP in tissues barriers has shown to be associated with altered pharmaco- and toxicokinetics of xenobiotics. Until now, little is known about the functional expression of this transporter in dairy animals. We therefore systematically examined the expression and subcellular localization of ABCG2/BCRP in small intestine, colon, lung, liver, kidney and mammary gland in lactating cows, sheep and goats. Carrier expression was investigated by RT-PCR and Western blot analysis showing highest expression of ABCG2/BCRP in small intestine and mammary gland, high levels in liver and moderate amounts of protein in lung, colon and kidney. Regarding subcellular localization, BCRP was predominantly found at the apical plasma membrane of small intestine, colon, bronchial epithelium, bile ducts and overall in endothelial structures in all tested species. In the mammary gland, there was strong apical staining of the alveolar epithelial cells and most of the ducts in all dairy ruminants. We also detected significantly elevated protein expression in lactating mammary gland compared with nonlactating cows, sheep and goats. Our results contribute to the role of BCRP in cytoprotection and disposition in important tissue barriers and may have important implications for veterinary pharmacotherapy of dairy animals using drugs identified as BCRP substrates.

Bioavailability and pharmacokinetics of oral meloxicam in llamas

Background

South American camelids in the United States have rapidly developed into an important agricultural industry in need of veterinary services. Pain management is challenging in camelids because there are no drugs currently approved by the U.S. Food and Drug Administration for use in these species. Dosage regimens used for many therapeutic drugs have been extrapolated from other ruminants; however, the pharmacokinetics, in camelids, may differ from those of other species. Studies investigating the pharmacokinetics of cyclooxygenase-2 (COX-2) selective non-steroidal anti-inflammatory drugs in camelids are deficient in the published literature. Six adult llamas (121- 168 kg) were administered either a 1 mg/kg dose of oral or a 0.5 mg/kg dose of IV meloxicam in a randomized cross-over design with an 11 day washout period between treatments. Plasma samples collected up to 96 hours post-administration were analyzed by high pressure liquid chromatography and mass spectrometry detection (HPLC-MS) followed by non-compartmental pharmacokinetic analysis.

Results

A mean peak plasma concentration (C_MAX) of 1.314 μg/mL (Range: 0.826 – 1.776 μg/mL) was recorded at 21.4 hours (Range: 12.0 – 24.0 hours) with a half-life (T ½ λ_z) of 22.7 hours (Range: 18.0 – 30.8 hours) after oral meloxicam administration. In comparison, a half-life (T ½ λ_z) of 17.4 hours (Range: 16.2 – 20.7 hours) was demonstrated with IV meloxicam administration. The oral bioavailability (F) of meloxicam (dose normalized) was 76% (Range: 48 – 92%). No adverse effects associated with either treatment modality were observed in the llamas.

Conclusions

The mean bioavailability (F) of oral meloxicam was 76% indicating a high degree of gastrointestinal absorption. Plasma meloxicam concentrations >0.2 μg/mL were maintained for up to 72 h after oral administration; >0.2 μg/mL is considered to be the concentration of meloxicam required for analgesic effects in other species such as the horse. These data suggest that a single dosage of oral meloxicam at 1 mg/kg could potentially maintain therapeutic concentrations in plasma for up to 3 days in adult llamas.

Role of the cytochrome P450 enzyme system in veterinary pharmacokinetics: where are we now? Where are we going?

Drug metabolism is a core determinant of the dose-effectiveness-toxicity relationship of many compounds. It is also critical to the human food safety assessment of drug residues in the edible tissues of food-producing animals. This article describes the current state of knowledge regarding the role of the cytochrome P450 superfamily of enzymes in determining the metabolic profile of compounds administered to companion animals (e.g., dog and cat) and to food-producing animal species (e.g., cattle, swine, chickens). In turn, this knowledge reflects the collection of insights derived from the recognized population variability observed in human drug metabolism, our general understanding of the kinetics of various drug-metabolism pathways, emerging tools that enable the role of pharmacogenetics to be studied and the characterization of drug metabolism in individual veterinary species. Ultimately, by increasing our insights with regard to factors that can influence drug metabolism, our knowledge of metabolic pathways, sources of within- and between-species variability in pharmacokinetics and the development of in silico models that can be used to predict pharmacokinetic profiles from these diverse sources of information. We will improve our ability to generate the population inferences needed to insure the target animal safety, product effectiveness and the human food safety of veterinary pharmaceuticals.

Patient variation in veterinary medicine--part II--influence of physiological variables

In veterinary medicine, the characterization of a drug's pharmacokinetic properties is generally based upon data that are derived from studies that employ small groups of young healthy animals, often of a single breed. In Part I of the series, we focused on the potential influence of disease processes, stress, pregnancy and lactation on drug pharmacokinetics. In this Part II of the series, we consider other covariates, such as gender, heritable traits, age, body composition, and circadian rhythms. The impact of these factors with respect to predicting the relationship between dose and drug exposure characteristics within an animal population is illustrated through the use of Monte Carlo simulations. Ultimately, an appreciation of these potential influences will improve the prediction of situations when dose adjustments may be appropriate.