Safety of a benazepril and pimobendan combination tablet in adult healthy dogs.

The objective of the study was to investigate the safety of a combination tablet of benazepril and pimobendan, Fortekor PLUS® , in a randomized, blinded, parallel-group design study in healthy adult beagle dogs. The test article, Fortekor PLUS® tablets, was administered orally twice daily for 6 months at one, two, and four times the highest recommended dosage of 0.5 mg/kg benazepril hydrochloride/0.25 mg/kg pimobendan (four males and four females per group). An additional control group was sham-dosed. Fortekor PLUS® did not induce any treatment-related effects on body weight, food consumption, neurological, ophthalmologic or physical assessments over the 6-month treatment period. The test article was possibly associated with an increased frequency of occasional vomiting. Fortekor PLUS® was associated with small, but significant, increases in heart rate and reductions in PR and QT intervals, which were assessed by electrocardiography. These effects were most probably related to reflex tachycardia secondary to reduced systemic blood pressure. Statistically significant changes in some clinical pathology variables were noted after test article administration, but were considered to be of no clinical relevance as values remained within reference ranges and/or were not dose-dependent. No treatment-related macroscopic or microscopic findings were observed. In conclusion, Fortekor PLUS® tablets were well tolerated in healthy adult dogs when administered at one, two, and four times the highest recommended dosage for 6 months.

Population pharmacokinetic analysis of blood concentrations of robenacoxib in dogs with osteoarthritis.

The purpose of this analysis was to investigate whether the recommended daily dosage of 1-2mg/kg robenacoxib provides consistent exposure when administered to dogs with chronic osteoarthritis (OA), and the need for dose adjustment in special patient populations. Data from three prospective, multi-center field studies in 208 OA dogs were analyzed using non-linear mixed effects modeling. A model based assessment was performed with stepwise inclusion and exclusion of population characteristics to explain between-subject variability, and assess the according necessity for dose adjustment. Only the influence of bodyweight on both apparent clearance and volume were found to be significant (p<0.01). No significant influence of sex, age and breed, or kidney and liver variables was identified in this representative sample of OA dogs. The population pharmacokinetic analysis performed showed that the 1-2mg/kg dosage chosen provided consistent robenacoxib exposure in a wide range of canine patients. No other dose adjustment seems necessary.

Capturing the dynamics of systemic Renin-Angiotensin-Aldosterone System (RAAS) peptides heightens the understanding of the effect of benazepril in dogs.

In dogs, activation of the Renin-Angiotensin-Aldosterone System (RAAS) is an important feature of congestive heart failure (CHF). Long-term increases in angiotensin II (AII) and aldosterone (ALD) lead to the progression of heart failure to its end stage. Angiotensin-converting enzyme inhibitors (ACEIs) are the foremost therapeutic option in the management of CHF. Recent literature has challenged the efficacy of ACEIs, based on modest reduction in urinary aldosterone (UALD) excretion despite marked inhibition of ACE activity. This study was designed to heighten the understanding of the effect of benazepril, a potent ACEI, on the RAAS, using a low-sodium diet as an experimental model of RAAS activation. Time course profiles of RAAS peptides and related areas under the curve (AUC) were used for comparison between benazepril and placebo groups. Results indicated substantial changes in the dynamics of these biomarkers. At presumed benazeprilat steady state, significant differences in AUC of plasma renin activity (+90%), angiotensin I (+43%), and AII (-53%) were found between benazepril and placebo-treated dogs. ALD decreased by 73% in plasma but only by 5% in urine. In conclusion, despite modest reduction in UALD excretion, benazepril markedly influences RAAS dynamics in dogs.

Paw inflammation model in dogs for preclinical pharmacokinetic/pharmacodynamic investigations of nonsteroidal anti-inflammatory drugs.

The goal of the present study was to develop and validate a new canine model of inflammation. The motivation was to make available a scientifically appropriate and ethically acceptable model to conduct pharmacokinetic/pharmacodynamic investigations for testing nonsteroidal anti-inflammatory drugs in dogs. A kaolin-induce paw inflammation model previously developed in cats was adapted to the dog. The paw inflammation developed within a few hours, reached maximum values 24 h and up to 3 days after kaolin administration, and then progressively resolved over 2 months. Five end points of clinical interest (body temperature, creeping time under a tunnel, paw withdrawal latency to a standardized thermal stimulus, lameness score, and vertical force developed during walking on a force plate) were measured regularly over the next 24 h and beyond to characterize the time development of the inflammation either in control conditions (placebo period) or after the administration of meloxicam (test period) according to a crossover design. Pharmacodynamic data were modeled using an indirect response pharmacokinetic/pharmacodynamic model. This model described three effects of meloxicam, namely, classic anti-inflammatory, analgesic, and antipyretic effects. The mean plasma meloxicam IC(50) values were 210 ng/ml for the antipyretic effect, 390 ng/ml for the analgesic effect, and 546 ng/ml for the vertical force exerted by the paw on the ground as measured by force plates. These in vivo IC(50) values require approximately 80 (antipyretic effect) to 90% (all other effects) cyclooxygenase-2 inhibition as calculated ex vivo whole-blood assay data.

Effect of route of administration on the efficacy and pharmacokinetics of an experimental formulation of the amino-acetonitrile derivative monepantel in sheep.

The effect of the route of administration (oral, intraruminal and intra-abomasal) on the efficacy and pharmacokinetics of the new anthelmintic monepantel in sheep was investigated. The target nematodes were fourth-stage Haemonchus contortus, Teladorsagia circumcincta, Trichostrongylus colubriformis and Cooperia curticei. A clear difference in efficacy was identified between the routes of administration, although the difference did not consistently reach statistical significance; oral treatment was most effective, followed by intraruminal and then intra-abomasal administration. The same pattern was observed in the pharmacokinetic analysis, with lambs treated orally having more favourable exposure to monepantel and its sulfone metabolite (albeit in all but one instance not significantly different) than the lambs treated by the other routes of administration, which were very similar for most parameters.

Pharmacokinetics of monepantel and its sulfone metabolite, monepantel sulfone, after intravenous and oral administration in sheep.

The pharmacokinetic properties of the developmental Amino-Acetonitrile Derivative (AAD), monepantel and its sulfone metabolite, monepantel sulfone were investigated in sheep following intravenous (i.v.) and oral administrations. The sulfone metabolite was rapidly formed and predominated over monepantel 4 h after dosing, irrespective of the route of administration. The steady-state volume of distribution, total body clearance and mean residence time of monepantel were 7.4 L/kg, 1.49 L/(kg x h) and 4.9 h, respectively and 31.2 L/kg, 0.28 L/(kg x h) and 111 h, respectively for monepantel sulfone. The overall bioavailability of monepantel was 31%, but it was demonstrated that approximately the same amount of monepantel sulfone was produced whether monepantel was given intravenously or orally (AUC((0-infinity)) oral/AUC((0-infinity)) i.v. of 94% for monepantel sulfone), making oral administration a very efficient route of administration for monepantel in terms of the amount of sulfone metabolite generated. Because monepantel sulfone is the main chemical entity present in sheep blood after monepantel administration and because it is also an active metabolite, its pharmacokinetic properties are of primary importance for the interpretation of future residue and efficacy studies. Overall, these pharmacokinetic data aid in the evaluation of monepantel as an oral anthelmintic in sheep.

Use of a pharmacokinetic/pharmacodynamic approach in the cat to determine a dosage regimen for the COX-2 selective drug robenacoxib.

This study investigated the analgesic, anti-inflammatory and antipyretic efficacy of the new COX-2 selective inhibitor robenacoxib in the cat and established pharmacodynamic (PD) parameters for these effects. Robenacoxib, at a dosage of 2 mg/kg administered subcutaneously, was evaluated in a kaolin-induced paw inflammation model in 10 cats, using both clinically relevant endpoints (lameness scoring, locomotion tests) and other indicators of inflammation (body and skin temperature, thermal pain threshold) to establish its pharmacological profile. A pharmacokinetic/pharmacodynamic (PK/PD) modelling approach, based on indirect response models, was used to describe the time course and magnitude of the responses to robenacoxib. All endpoints demonstrated good responsiveness to robenacoxib administration and both the magnitude and time courses of responses were well described by the indirect pharmacodynamic response models. Pharmacokinetic and clinically relevant pharmacodynamic parameters were used to simulate dosage regimens that will assist the planning of clinical trials and the selection of an optimal dosage regimen for robenacoxib in the cat.

Differential inhibition of cyclooxygenase isoenzymes in the cat by the NSAID robenacoxib.

Robenacoxib is a new nonsteroidal anti-inflammatory drug (NSAID) developed for use in companion animal medicine. The objectives of this study were: to quantify the inhibitory actions of robenacoxib on cyclooxygenase (COX) isoenzymes in feline whole blood assays; to establish blood concentration-time profiles of robenacoxib after intravenous and subcutaneous dosing in the cat and; to predict the time courses of inhibition of COX isoforms by robenacoxib. COX-1 and COX-2 activities in heparinized feline whole blood samples were induced with calcium ionophore and lipopolysaccharide, respectively. Inhibition of thromboxane B2 provided a marker of both COX-1 and COX-2 activities and a nonlinear parametric mixed effects modelling approach was used to establish the pharmacodynamic parameters describing this inhibition. Mean values (and prediction intervals) of IC50 were 28.9 (16.4-51.1) microM (COX-1) and 0.058 (0.010-0.340) microM (COX-2). These parameters were used to compute several selectivity indices. Selectivity IC ratios (COX-1:COX-2) were 502.3 (IC50/IC50), 451.6 (IC95/IC95) and 17.05 (IC20/IC80). Based on a clinically recommended dosage regimen of 2 mg/kg, it was predicted that the corresponding mean robenacoxib blood concentration over the first 12 h after drug administration corresponded to 5% inhibition of COX-1 and 90% inhibition of COX-2.

Development and validation of a new model of inflammation in the cat and selection of surrogate endpoints for testing anti-inflammatory drugs.

In laboratory animals many models of inflammation have been developed for preclinical evaluation of the pharmacological profiles of nonsteroidal anti-inflammatory drugs (NSAIDs). In contrast, in species of veterinary interest, including the cat, NSAIDs have been studied mainly using dose-titration or dose-confirmation studies in clinical subjects. This is due to the scarcity of appropriate animal models and to the associated lack of quantitative validated endpoints describing the magnitude and time course of drug response. Determination of pharmacokinetic/pharmacodynamic (PK/PD) relationships provides a powerful approach for the selection of effective and safe dosage regimens. In this study, a paw inflammation model in the cat was developed for the preclinical evaluation of NSAIDs using PK/PD modelling. Subcutaneous injection of 500 mg kaolin in the paw produced a well-defined and reproducible inflammatory response that lasted 4-5 days. Several endpoints were assessed for their clinical relevance and for their metrological performance (accuracy and reproducibility). Body temperature, lameness scoring, locomotion tests and possibly skin temperature were the most appropriate endpoints for testing the antipyretic, analgesic and anti-inflammatory effects of NSAIDs in the cat.