Pharmacodynamics and enantioselective pharmacokinetics of racemic carprofen in the horse

The effect of intravenous lipid emulsion (ILE) on the pharmacokinetic/toxicokinetic dispositions of ivermectin and carprofen in rabbits

Intravenous lipid emulsion (ILE) has been widely used as an effective antidote in both veterinary and human medicine for the treatment of acute intoxications caused by drugs and pesticides with high lipid solubility. This study was conducted to investigate the effect of ILE co-administration on the kinetic dispositions of ivermectin (IVM) and carprofen (CRP) following intravenous bolus administration at subtoxic doses in rabbits.Twenty-four male New Zealand rabbits weighing 2.78 ± 0.2 kg were used in this study. Rabbits were divided into four groups (Group 1: IVM and Group 2: IVM + ILE or Group 3: CRP and Group 4: CRP + ILE), each group consisting of 6 animals. In the IVM study, Group 1 received IVM (0.6 mg/kg) alone while Group 2 received IVM (0.6 mg/kg) and ILE (2.5 ml/kg). In the CRP study, Group 3 received CRP (12 mg/kg) alone while Group 4 received CRP (12 mg/kg) and ILE (2.5 ml/kg). In both drug groups, ILE was administered 3 times as an i.v. bolus at the 10th min and repeated 4th and 8th h after the drug administration. Blood samples were collected from the auricular vein at various times after drug administration. The drug concentrations in plasma samples were determined by high-pressure liquid chromatography. Kinetic parameters were calculated using a non-compartmental model for both CRP and IVM.The C0 and area under the concentration-time curve from zero up to ∞ (AUC0-∞) values were significantly greater with ILE co-administration (2136 ng/ml and 360.84 ng.d/ml) compared to the IVM alone (1340.63 ng/ml and 206 ng.d/ml), respectively. Moreover, the volume of distribution (Vdss) and clearance (Cl) of IVM were reduced by approximately 42% and 46% with ILE co-administration compared to IVM alone resulting in a reduction of the distribution and slower elimination, respectively. Similar differences in C0, and Vdss values were also observed in CRP with ILE co-administration compared to CRP alone. ILE co-administration changed significantly the kinetic profile of both IVM and CRP in rabbits, supporting the lipid sink theory in which highly lipid-soluble compounds are absorbed into the lipid phase of plasma from peripheral organs such as the heart and brain affected by the acute toxicity of the compounds.

The Clinical Pharmacology and Therapeutic Evaluation of Non-Steroidal Anti-Inflammatory Drugs in Adult Horses

This review firstly examines the underlying pathophysiology of pain and inflammation associated with orthopedic disease and endotoxemia. Then, it reviews the clinical pharmacology (pharmacokinetics and pharmacodynamics) of both conventional and non-conventional NSAIDs in the adult horse, and finally provides an overview of different modalities to evaluate the therapeutic efficacy of NSAIDs in research.

The Surface Area to Volume Ratio Changes the Pharmacokinetic and Pharmacodynamic Parameters in the Subcutaneous Tissue Cage Model: As Illustrated by Carprofen in Sheep

Introduction

Pharmacokinetic and pharmacodynamic models can be powerful tools for predicting outcomes. Many models are based on repetitive sampling of the vascular space, due to the simplicity of obtaining samples. As many drugs do not exert their effect in the vasculature, models have been developed to sample tissues outside the bloodstream. Tissue cages are hollow devices implanted subcutaneously, or elsewhere, that are filled with fluid allowing repetitive sampling to occur. The physical dimensions of the cage, namely, the diffusible surface area to volume ratio, would be expected to change the rate of drug movement into and out of tissue cages.

Methods

Seven sheep were implanted with five pairs of tissue cages, subcutaneously. Each pair of cages had a different length but a fixed diffusible surface area, so the surface area to volume ratio differed. Carrageenan was injected into half of the cages in each animal during one sampling period in a cross-over design. Samples from each cage and the bloodstream were obtained at 14-time points during two sampling periods. The concentration of carprofen was measured using LC–MS/MS and the results were modeled using nonlinear mixed-effects techniques. Prostaglandin metabolites were also measured and the change over time was analyzed using linear mixed effect modeling.

Results

The presence of carrageenan within an animal changed the systemic pharmacokinetics of carprofen. The rate of drug movement into and out of the tissue cages varied with the surface area to volume ratio. The concentration time curve for prostaglandin metabolites changed with cage size.

Conclusion

The surface area volume ratio of tissue cages will influence the calculated pharmacokinetic parameters and may affect calculated pharmacodynamics, thus, it is an important factor to consider when using tissue cage data for dosing regimes.

Pharmacokinetics and bioavailability of carprofen in sheep

The aim of this study was to determine the pharmacokinetics and bioavailability of carprofen in sheep following single intravenous (IV), intramuscular (IM), subcutaneous (SC), and oral (PO) administrations of a parenteral formulation at a dose of 4 mg/kg. A total of eight sheep were used for the investigation. The study comprised four periods, according to a crossover design with a 21-day washout period between treatments. Plasma concentrations of carprofen were measured using HPLC-UV. Pharmacokinetic parameters were estimated by non-compartmental model analysis. Following IV administration, t_1/2ʎz , Cl_T , and V_dss were 43.36 h, 1.98 ml/h/kg, and 121.36 ml/kg, respectively. The C_max(obs) was 26.57 mg/ml for the IM, 23.76 mg/ml for the SC, and 15.90 mg/ml for the PO. The bioavailability following IM, SC, and PO administrations was 75.47%, 82.00%, and 62.51%, respectively. Plasma creatine kinase activity increased significantly at 3, 6, and 12 h following IM administration of carprofen. Despite differences in plasma concentrations and bioavailability among administration routes, carprofen at 4 mg/kg dose may provide the plasma concentration (>1.5 μg/ml) needed for analgesic effect during 144 h in all routes. However, because of the slow absorption rate after SC and PO routes, the IV route may be preferred primarily for the rapid onset in the analgesic and anti-inflammatory effect of carprofen in sheep. Despite the favorable kinetics, the muscle damage caused by IM injection limits use of carprofen via IM route.

Swine as the Animal Model for Testing New Formulations of Anti-Inflammatory Drugs: Carprofen Pharmacokinetics and Bioavailability of the Intramuscular Route

Carprofen (CP) is a non-steroidal anti-inflammatory drug (NSAID) frequently used to treat respiratory diseases in numerous small animals, but also in large species. CP is a formidable candidate for further therapeutic research of human inflammatory diseases using the pig as an animal model. However, CP administration in swine is very uncommon and respective pharmacokinetics/bioavailability studies are scarce. A simultaneous population pharmacokinetic analysis after CP intravenous and intramuscular administrations in pigs has shown high extent and rate of absorption and a similar distribution profile with respect to man and other mammals. However, clearance and half-life values found in swine suggest a slower elimination process than that observed in man and some other animal species. Although not reported in other species, liver and kidney concentrations achieved at 48 h post-intramuscular administration in pigs were ten times lower than those found in plasma. Simulations pointed to 4 mg/kg every 24 h as the best dosage regimen to achieve similar therapeutic levels to those observed in other animal species. All these findings support the use of pig as an animal model to study the anti-inflammatory effects of CP in humans.

In vivo pharmacokinetic evaluation of carprofen delivery from intra-articular nanoparticles in rabbits: A population modelling approach

Osteoarthritis is treated with COX or fosfolipase A2 inhibitors such as carprofen, a propionic acid NSAID. The enhancement of its action over the articular cartilage is mandatory to facilitate its therapeutic application. Drug uptake into the cartilage requires high synovial fluid concentrations, anticipating its rapid distribution towards bloodstream. Thus, intraarticular administration improves local targeting of the drug, lining with the site of action. A pharmacokinetic study in rabbits has been performed to evaluate carprofen nanoparticles after intraarticular administration. Pharmacokinetic analysis of plasma profiles through a modelling approach, has demonstrated the rapid distribution of drug outside of synovial chamber but mainly remaining in plasma. The data modelling has demonstrated the existence of two release-absorption processes when the nanoparticles are administered in the synovial space. Additionally, results are predictive of the PK profile of some other species such as cat, dogs or humans.

Analgesia for Sheep in Commercial Production: Where to Next?

Simple Summary

Increasing societal and customer pressure to provide animals with ‘a life worth living’ continues to apply pressure on industry to alleviate pain associated with husbandry practices, injury and illness. Although a number of analgesic solutions are now available for sheep, providing some amelioration of the acute pain responses, this review has highlighted a number of potential areas for further research.

Abstract

Increasing societal and customer pressure to provide animals with ‘a life worth living’ continues to apply pressure on livestock production industries to alleviate pain associated with husbandry practices, injury and illness. Over the past 15–20 years, there has been considerable research effort to understand and develop mitigation strategies for painful husbandry procedures in sheep, leading to the successful launch of analgesic approaches specific to sheep in a number of countries. However, even with multi-modal approaches to analgesia, using both local anaesthetic and non-steroidal anti-inflammatory drugs (NSAID), pain is not obliterated, and the challenge of pain mitigation and phasing out of painful husbandry practices remains. It is timely to review and reflect on progress to date in order to strategically focus on the most important challenges, and the avenues which offer the greatest potential to be incorporated into industry practice in a process of continuous improvement. A structured, systematic literature search was carried out, incorporating peer-reviewed scientific literature in the period 2000–2019. An enormous volume of research is underway, testament to the fact that we have not solved the pain and analgesia challenge for any species, including our own. This review has highlighted a number of potential areas for further research.

BEVA primary care clinical guidelines: Analgesia

Primary care guidelines provide a reference point to guide clinicians based on a systematic review of the literature, contextualised by expert clinical opinion. These guidelines develop a modification of the GRADE framework for assessment of research evidence (vetGRADE) and applied this to a range of clinical scenarios regarding use of analgesic agents. Key guidelines produced by the panel included recommendations that horses undergoing routine castration should receive intratesticular local anaesthesia irrespective of methods adopted and that horses should receive NSAIDs prior to surgery (overall certainty levels high). Butorphanol and buprenorphine should not be considered appropriate as sole analgesic for such procedures (high certainty). The panel recommend the continuation of analgesia for 3 days following castration (moderate certainty) and conclude that phenylbutazone provided superior analgesia to meloxicam and firocoxib for hoof pain/laminitis (moderate certainty), but that enhanced efficacy has not been demonstrated for joint pain. In horses with colic, flunixin and firocoxib are considered to provide more effective analgesia than meloxicam or phenylbutazone (moderate certainty). Given the risk of adverse events of all classes of analgesic, these agents should be used only under the control of a veterinary surgeon who has fully evaluated a horse and developed a therapeutic, analgesic plan that includes ongoing monitoring for such adverse events such as the development of right dorsal colitis with all classes of NSAID and spontaneous locomotor activity and potentially ileus with opiates. Finally, the panel call for the development of a single properly validated composite pain score for horses to allow accurate comparisons between medications in a robust manner.

Pharmacokinetics of meloxicam after oral administration of a granule formulation to healthy horses

Background

Nonsteroidal anti‐inflammatory drugs are administered in horses for several systemic diseases. Selective cyclooxygenase‐2 inhibitors are preferred because of lower risk of adverse effects. Several meloxicam formulations have been tested in horses, but a recently marketed granule oral formulation has not been studied.

Objective

To characterize the pharmacokinetics of a novel granule meloxicam formulation in fasted and fed horses, and to compare pharmacokinetic features with oral suspension and tablets.

Animals

Seven healthy adult horses.

Methods

Meloxicam was administered at 0.6 mg/kg in fasted or fed horses. Blood samples were collected for pharmacokinetic analysis, and vital signs, hematology, and biochemistry variables were monitored for 72 hours.

Results

No adverse effects were detected. Volume of distribution and clearance after intravenous administration of meloxicam were 0.36 L/kg and 29.12 mL/h/kg, respectively, with a 12.39 hours of terminal half‐life. Protein binding was of 97%. Bioavailability was high for every oral formulation, ranging 70%‐110%, without feed effect. Because of a slower absorption, meloxicam after administration of granules had a longer half‐life (24 and 34 hours, fasted and fed, respectively) and mean residence time (31 and 47 hours), than suspension and tablets (ranging 10‐13 and 13‐15 hours, respectively). In addition, the time above therapeutic concentration was higher for the granule formulation than other formulations.

Conclusions and Clinical Importance

Granule formulation has different PK parameters compared to other oral formulations, which could enable this formulation to be used for different dosage regimens in order to reach a desired clinical effect or decrease the risk of adverse effects.

A study of the pharmacokinetics and thromboxane inhibitory activity of a single intramuscular dose of carprofen as a means to establish its potential use as an analgesic drug in white rhinoceros

The alleviation of pain and prevention of suffering are key aspects of animal welfare. Unfortunately, analgesic drugs are not available for all species. White rhinoceros (Ceratotherium simum), representing one of such species, which survive poaching attempts inflicted with severe facial injuries and gunshot wounds, nonetheless require analgesic support. To improve treatment conditions, this study explored the use of carprofen for the treatment of pain and inflammation in white rhinoceros. The pharmacokinetics of 1 mg/kg intramuscular carprofen was evaluated in six healthy white rhinoceros. The half-life of λ_z and mean residence time was 105.71 ± 15.67 and 155.01 ± 22.46 hr, respectively. The area under the curve and the maximum carprofen concentration were 904.61 ± 110.78 μg ml^-1  hr^-1 and 5.77 ± 0.63 μg/ml, respectively. Plasma TXB₂ inhibition demonstrated anti-inflammatory properties and indicated that carprofen may be effective for a minimum of 48 hr in most animals. With its long half-life further indicating that a single dose could be effective for several days, we suggest that carprofen may be a useful drug for the treatment of white rhinoceros.

Analysis of loxoprofen in tablets, patches, and equine urine as tert-butyldimethylsilyl derivative by gas chromatography-mass spectrometry

Loxoprofen is a non-steroidal anti-inflammatory drug of the 2-arylpropionic acid type, which has used to treat musculoskeletal disorders in the horse racing industry. However, it has also used illicitly to mask clinical signs of inflammation and pain in racehorses. Thus, its accurate analysis has become an important issue in horse doping laboratories. In this study, an analytical method of loxoprofen was developed as tert-butyldimethylsilyl (TBDMS) derivative by gas chromatography-mass spectrometry (GC-MS). Characteristic fragment ions of [M-15], [M-57], and [M-139] permitted the accurate and selective detection of loxoprofen. Under optimal conditions, this method showed good linearity (r ≥ 0.999) in the range of 10-500 ng/mL, repeatability (% relative standard deviation = 5.6-8.5), and accuracy (% relative error = - 0.3-0.9) with a detection limit of 1.0 ng. When applied to the analysis of loxoprofen in tablet and patch products, loxoprofen was positively identified as TBDMS derivative by GC-MS. The present method provided rapid and accurate determination of loxoprofen in patch and tablet products. Levels of loxoprofen were highest in equine urine at 0.5 and 1 h after oral administration with single dose (3 mg/kg) to three horses, and then rapidly reduced to below the lower limit of quantification at 24 h. Therefore, the present method will be useful for the pharmacokinetic study and doping tests for loxoprofen and other similar acidic drugs in horses.

The use of nonsteroidal anti-inflammatory drugs in critically ill horses

OBJECTIVE

To review the physiology of the cyclooxygenase (COX) enzymes with reference to the beneficial effects of nonsteroidal anti-inflammatory drugs (NSAIDs) related to their analgesic and antiendotoxic properties as well as the mechanisms responsible for adverse gastrointestinal, renal, and coagulation effects.

DATA SOURCES

Human and veterinary peer reviewed literature

VETERINARY DATA SYNTHESIS

NSAIDs are frequently administered to critically ill horses for their analgesic and anti-inflammatory effects. However, NSAIDs have significant side effects principally on the gastrointestinal mucosa and kidneys. These side effects may be exacerbated in critically ill horses if they have gastrointestinal damage or are volume depleted

CONCLUSIONS

This review provides important information for equine veterinarians and criticalists on the advantages and disadvantages of using traditional NSAIDs and newer equine COX-2 selective NSAIDs for the management of different conditions in critically ill horses.

Influence of oxytetracycline on carprofen pharmacodynamics and pharmacokinetics in calves

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

Potency and selectivity of carprofen enantiomers for inhibition of bovine cyclooxygenase in whole blood assays

Whole blood in vitro assays were used to determine the potency and selectivity of carprofen enantiomers for inhibition of the isoforms of cyclooxygenase (COX), COX-1 and COX-2, in the calf. S(+)-carprofen possessed preferential activity for COX-2 inhibition but, because the slopes of inhibition curves differed, the COX-1:COX-2 inhibition ratio decreased from 9.04:1 for inhibitory concentration (IC)10 to 1.84:1 for IC95. R(-) carprofen inhibited COX-2 preferentially only for low inhibition of the COX isoforms (IC10 COX-1:COX-2=6.63:1), whereas inhibition was preferential for COX-1 for a high level of inhibition (IC95 COX-1:COX-2=0.20:1). S(+) carprofen was the more potent inhibitor of COX isoforms; potency ratios S(+):R(-) carprofen were 11.6:1 for IC10 and 218:1 for IC90. Based on serum concentrations of carprofen enantiomers obtained after administration of a therapeutic dose of 1.4 mg/kg to calves subcutaneously, S(+)-carprofen concentrations exceeded the in vitro IC80 COX-2 value for 32 h and the IC20 for COX-1 for 33 h. The findings are discussed in relation to efficacy and safety of carprofen in calves.

Avian analgesia

Avian analgesia is now recognized as a critical component of avian medicine and surgery. The need to recognize pain and to provide pain relief is the first step, and many anecdotal therapeutic doses have been extrapolated from other companion animals. Several published research investigations, using several species of birds, have begun to provide avian analgesia therapeutic information for clinical application. The challenge is to continue pushing this research forward with appreciation that there are approximately 10,000 known species of birds, perhaps 200 species commonly kept as pets, and that each species has a range of behaviors as varied as their species-specific PKs and PDs to each analgesic drug.

Pharmacokinetics and metabolism of orally administered firocoxib, a novel second generation coxib, in horses

The primary objective of this study was to determine the pharmacokinetic profile of firocoxib, a novel second generation coxib, in horses. Horses were administered either a single oral or intravenous dose of firocoxib at 0.1 mg/kg in a two-period crossover study with 12 animals. The dosage was based on previously determined pharmacodynamic parameters. Oral firocoxib was well absorbed with an average bioavailability (absolute) of 79% and a Cmax of 75 ng/mL at 3.9 h. The average elimination half-life was 30 h. Following intravenous administration the average Cmax was 210 ng/mL and the elimination half-life was 34 h. The area under the curve [AUC(0-tlast)] was 1.8 microg.h/mL for the oral dose and 2.3 microg.h/mL for the intravenous dose. Firocoxib was widely distributed with a volume of distribution value of 1.7 L/kg for the intravenous dose. Biotransformation of firocoxib was via dealkylation and glucuronidation to inactive metabolites, namely descyclopropylmethylfirocoxib and its glucuronide conjugate. Urinary excretion was the major route of elimination, and the clearance rate was 37 mL/h/kg.

Drug distribution and stability in extemporaneous preparations of meloxicam and carprofen after dilution and suspension at two storage temperatures

OBJECTIVE

To determine dispersion uniformity and stability of meloxicam and carprofen in extemporaneous preparations stored for 28 days.

DESIGN

Prospective study.

SAMPLE POPULATION

Meloxicam and carprofen (commercial formulations) were compounded (day 0) with deionized water (DW), 1% methylcellulose gel (MCG), MCG and simple syrup (SS; 1:1 mixture), or a suspending and flavoring vehicle combination (SFVC; 1:1 mixture) to nominal drug concentrations of 0.25, 0.5, or 1.0 mg/mL and 1.25, 2.5, or 5.0 mg/mL, respectively.

PROCEDURES

Preparations were stored at approximately 4 degrees C (39.2 degrees F) or 22 degrees C (71.6 degrees F). For each preparation, drug concentrations were determined and drug stability was evaluated at intervals during storage; on days 0 and 28, pH values were measured and bacterial cultures were initiated.

RESULTS

In meloxicam-DW, meloxicam-MCG (0.25 mg/mL), and meloxicam-MCG (0.5 mg/mL) preparations, drug distribution was uniform (coefficient of variation < 10%); > 90% of the original drug concentration was maintained for 28 days. Despite uniform drug distribution of the carprofen-SFVC preparations, most retained > or = 90% of the original drug concentration for only 21 days. Use of the MCG-SS combination resulted in foamy preparations of unacceptable variability. After 28 days, pH decreased slightly in meloxicam-DW and meloxicam-MCG preparations (0.17 +/- 0.04 and 0.21 +/- 0.04, respectively). Carprofen-SFVC (2.5 mg/mL) and carprofen-MCG-SS (5.0 mg/mL) preparations stored at 22 degrees C for 28 days yielded bacterial growth.

CONCLUSIONS AND CLINICAL RELEVANCE

DW, MCG, and the SFVC can be used successfully for extemporaneous preparation of meloxicam and carprofen for administration to small exotic animals. Refrigeration is recommended for preparations of meloxicam-DW and carprofen-SFVC.

Pharmacokinetics of R(-) and S(+) carprofen after administration of racemic carprofen in donkeys and horses

OBJECTIVE

To compare plasma disposition of the R(-) and S(+) enantiomers of carprofen after IV administration of a bolus dose to donkeys and horses.

ANIMALS

5 clinically normal donkeys and 3 clinically normal horses.

PROCEDURE

Blood samples were collected from all animals at time 0 (before) and at 10, 15, 20, 30, and 45 minutes and 1, 1.5, 2, 2.5, 3, 4, 5, 6, 8, 10, 24, 28, 32, and 48 hours after IV administration of a bolus of carprofen (0.7 mg/kg). Plasma was analyzed in triplicate via high-performance liquid chromatography to determine the concentrations of the carprofen enantiomers. A plasma concentrationtime curve for each donkey and horse was analyzed separately to estimate noncompartmental pharmacokinetic variables.

RESULTS

In donkeys and horses, the area under the plasma concentration versus time curve (AUC) was greater for the R(-) carprofen enantiomer than it was for the S(+) carprofen enantiomer. For the R(-) carprofen enantiomer, the AUC and mean residence time (MRT) were significantly less and total body clearance (CIT) was significantly greater in horses, compared with donkeys. For the S(+) carprofen enantiomer, AUC and MRT were significantly less and CIT and apparent volume of distribution at steady state were significantly greater in horses, compared with donkeys.

CONCLUSIONS AND CLINICAL RELEVANCE

Results have suggested that the dosing intervals for carprofen that are used in horses may not be appropriate for use in donkeys.

Pharmacokinetics and synovial fluid concentrations of flurbiprofen enantiomers in horses: chiral inversion

Flurbirpofen (FBP), a member of the 2-aryl propionate nonsteroidal anti-inflammatory drug class, has potent anti-inflammatory and analgesic properties. The commercial preparation is a racemic mixture of the R(-) and S(+) enantiomers of FBP. In this study, R(-) and S(+) FBP were used to investigate the metabolic chiral inversion. Each enantiomer was administered separately (0.25 mg/kg) and in a racemic mixture (0.5 mg/kg) intravenously to horses. Plasma and synovial concentration of each enantiomer was determined and the disposition of each was analyzed. After intravenous administration of R(-) FBP and S(+) FBP to horses no chiral inversion was detected. After the administration of the FBP racemate and individual enantiomers no differences were observed between pharmacokinetic parameters [t(1/2beta) (h), Cl (L/h.kg), AUC (microg.h/mL), Vss (L/kg) and MRT (h)] for R(-) and S(+) FBF. Synovial fluid concentrations of both FBP enantiomers were lower than plasma concentrations and no stereoselective differences were detected. These data indicate that the disposition of FBF in horses is not enantioselective and demonstrate a difference in the pharmacokinetic behavior of the enantiomers as compared with other 2-aryl-propionic acids, such as carprofen, ketoprofen and vedaprofen in the horse.

Pharmacodynamics and pharmacokinetics of nonsteroidal anti-inflammatory drugs in species of veterinary interest

This review summarises selected aspects of the pharmacokinetics (PK) and pharmacodynamics (PD) of nonsteroidal anti-inflammatory drugs (NSAIDs). It is not intended to be comprehensive, in that it covers neither minor species nor several important aspects of NSAID PD. The limited objective of the review is to summarise those aspects of NSAID PK and PD, which are important to an understanding of PK-PD integration and PK-PD modelling (the subject of the next review in this issue). The general features of NSAID PK are: usually good bioavailability from oral, intramuscular and subcutaneous administration routes (but with delayed absorption in horses and ruminants after oral dosing), a high degree of binding to plasma protein, low volumes of distribution, limited excretion of administered dose as parent drug in urine, marked inter-species differences in clearance and elimination half-life and ready penetration into and slow clearance from acute inflammatory exudate. The therapeutic effects of NSAIDs are exerted both locally (at peripheral inflammatory sites) and centrally. There is widespread acceptance that the principal mechanism of action (both PD and toxicodynamics) of NSAIDs at the molecular level comprises inhibition of cyclooxygenase (COX), an enzyme in the arachidonic acid cascade, which generates inflammatory mediators of the prostaglandin group. However, NSAIDs possess also many other actions at the molecular level. Two isoforms of COX have been identified. Inhibition of COX-1 is likely to account for most of the side-effects of NSAIDs (gastrointestinal irritation, renotoxicity and inhibition of blood clotting) but a minor contribution also to some of the therapeutic effects (analgesic and anti-inflammatory actions) cannot be excluded. Inhibition of COX-2 accounts for most and possibly all of the therapeutic effects of NSAIDs. Consequently, there has been an intensive search to identify and develop drugs with selectivity for inhibition of COX-2. Whole blood in vitro assays are used to investigate quantitatively the three key PD parameters (efficacy, potency and sensitivity) for NSAID inhibition of COX isoforms, providing data on COX-1:COX-2 inhibition ratios. Limited published data point to species differences in NSAID-induced COX inhibition, for both potency and potency ratios. Members of the 2-arylpropionate sub-groups of NSAIDs exist in two enantiomeric forms [R-(-) and S-(+)] and are licensed as racemic mixtures. For these drugs there are marked enantiomeric differences in PK and PD properties of individual drugs in a given species, as well as important species differences in both PK and PD properties.

PK-PD integration and PK-PD modelling of nonsteroidal anti-inflammatory drugs: principles and applications in veterinary pharmacology

Much useful information relevant to elucidation of mechanism of action of nonsteroidal anti-inflammatory drugs (NSAIDs) at the molecular level can be obtained from integrating pharmacokinetic (PK) and pharmacodynamic (PD) data, such data being obtained usually, although not necessarily, in separate studies. Integrating PK and PD data can also provide a basis for selecting clinically relevant dosing schedules for subsequent evaluation in disease models and clinical trials. The principles underlying and uses of PK-PD integration are illustrated in this review for phenylbutazone in the horse and cow, carprofen and meloxicam in the horse, carprofen and meloxicam in the cat and nimesulide in the dog. In the PK-PD modelling approach for NSAIDs, the PK and PD data are generated (usually though not necessarily) in vivo in the same investigation and then modelled in silico, usually using the integrated effect compartment or indirect response models. Drug effect is classically modelled with the sigmoidal E(max) (Hill) equation to derive PD parameters which define efficacy, potency and sensitivity. The PK-PD modelling approach for NSAIDs can be undertaken at the molecular level using surrogates of inhibition of cyclooxygenase (COX) isoforms (or indeed other enzymes e.g. 5-lipoxygenase). Examples are provided of the generation of PD parameters for several NSAIDs (carprofen, ketoprofen, vedaprofen, flunixin and tolfenamic acid) in species of veterinary interest (horse, calf, sheep and goat), which indicate that all drugs investigated except vedaprofen were non-selective for COX-1 and COX-2 in the four species investigated under the experimental conditions used, vedaprofen being a COX-1 selective NSAID. In these studies, plasma concentration was linked to COX inhibitory action in the biophase using an effect compartment model. Data for S-(+)-ketoprofen have been additionally subjected to inter-species modelling and allometric scaling of both PK and PD parameters. For several species values of four PK parameters were highly correlated with body weight, whilst values for PD parameters based on COX inhibition lacked allometric relationship with body weight. PK-PD modelling of NSAIDs has also been undertaken using clinical end-points and surrogates for clinical end-points in disease models. By measurement of clinically relevant indices in clinically relevant models, data generated for PD parameters have been used to set dosages and dose intervals for evaluation and confirmation in clinical trials. PK-PD modelling of NSAIDs is likely to prove superior to conventional dose titration studies for dosage schedule determination, as it sweeps the whole of the concentration-effect relationship for all animals and therefore permits determination of genuine PD parameters. It also introduces time as a second independent variable thus allowing prediction of dosage interval. Using indirect response models and clinically relevant indices, PD data have been determined for flunixin, phenylbutazone and meloxicam in the horse, nimesulide in the dog and meloxicam in the cat.

Pharmacology of drugs used to treat osteoarthritis in veterinary practice

As in humans, pain in animals may be associated with a wide range of conditions and circumstances, ranging from acute trauma to joint diseases. Joint diseases are common in companion animal medicine (horse, dog, cat) and at least 80% of cases are classified as osteoarthritis (OA). Several drug classes are available for OA therapy, including corticosteroids, non-steroidal antiinflammatory drugs (NSAIDs), agents with potential disease modifying properties and nutraceuticals. For long-term maintenance OA treatment, particularly in the horse and dog, NSAIDs are routinely and extensively used. This review outlines the pharmacokinetics (PK) and pharmacodynamics (PD) of NSAIDs in companion and farm animal species. NSAID PK and PD have been studied in models of acute inflammation, which enable use of PK-PD modeling to facilitate (a) studies of mechanism of action at the molecular level and (b) prediction of dosages for clinical use. The PK-PD approach is a powerful but underutilized tool which also facilitates inter-species comparisons.

Clinical efficacy of carprofen as an adjunct to the antibacterial treatment of bovine respiratory disease

A clinical trial was undertaken to investigate the efficacy of a single dose of carprofen (CPF) in the treatment of bovine respiratory disease in cattle. Tilmicosin was used as a basal treatment in all animals. Six hours after dosing, body temperature and respiratory rates in animals treated with CPF-tilmicosin had decreased and were significantly lower than in the animals treated with tilmicosin alone (P < 0.05). Over the period of clinical observation, CPF-tilmicosin treatment produced a clinical resolution of the pneumonia similar to treatment with tilmicosin alone. However, it is significant from an animal welfare perspective that over the period of the study after treatment, CPF-tilmicosin therapy produced significantly greater symptomatic improvement than tilmicosin.

Effect of topical application of diclofenac liposomal suspension on experimentally induced subcutaneous inflammation in horses

OBJECTIVE

To determine whether 1% diclofenac liposomal suspension (DLS) ointment would be absorbed transdermally and attenuate experimentally induced subcutaneous inflammation in horses.

ANIMALS

7 healthy adult horses.

PROCEDURE

Inflammation was produced by injecting 1% sterile carrageenan into subcutaneously implanted tissue cages 8 hours before (time -8) and at the time of application of test ointment. A crossover design was used. Horses received 1 of 2 treatments (topically administered control or DLS ointments) during 48 hours of carrageenan-induced subcutaneous inflammation. A single application of test ointment (7.2 g) was applied over each tissue cage (time 0). Samples of transudate and blood were collected at -8, 0, 6, 12, 18, 24, 30, 36, and 48 hours. Plasma and transudate diclofenac concentrations were determined by use of high-performance liquid chromatography. Transudate concentrations of prostaglandin E2 (PGE2) were determined with a competitive enzyme immunoassay.

RESULTS

DLS was absorbed transdermally. The highest concentration (mean +/- SEM, 76.2 +/- 29 ng/mL) was detectable in tissue-cage fluid within 18 hours after application. Minimal concentrations of diclofenac were detectable in plasma. Application of DLS significantly decreased transudate concentrations of PGE2 at 6 and 30 hours. Decreases in PGE2 concentration were observed in the DLS group at all collection times.

CONCLUSIONS AND CLINICAL RELEVANCE

A single topical application of DLS resulted in concentrations of diclofenac in transudate within 6 hours and significantly attenuated carrageenan-induced local production of PGE2. Results of this study suggest that DLS is readily absorbed transdermally and may be efficacious for reducing subcutaneous inflammation in horses.