Pharmacokinetics, pharmacodynamics, toxicology and therapeutics of mavacoxib in the dog: a review

Treatment of Pain in Birds

This article provides an overview of the current understanding of evidence-based clinical analgesic use in birds. The field of avian analgesia has dramatically expanded during the last 20 years, affording more options for alleviating both acute and chronic pain. These options include opioids, nonsteroidal anti-inflammatory drugs, local anesthetics, and/or other drugs like gabapentin, amantadine, and cannabinoids, acting at different points in the nociceptive system thereby helping to provide greater pain relief while reducing the risk of adverse effects when combined.

Advances in the pharmaceutical treatment options for canine osteoarthritis

Canine osteoarthritis is a significant cause of pain in many dogs and can therefore compromise animal welfare. As the understanding of the biology and pain mechanisms underpinning osteoarthritis grows, so do the number of treatments available to manage it. Over the last decade, there have been a number of advances in the pharmaceutical treatment options available for dogs with osteoarthritis, as well as an increasing number of clinical trials investigating the efficacy of pre-existing treatments. This review aims to examine the current evidence behind pharmaceutical treatment options for canine osteoarthritis, including non-steroidal anti-inflammatory drugs, piprants, monoclonal antibodies, adjunctive analgesics, structure modifying osteoarthritis drugs and regenerative therapies.

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

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

Selective inhibition of cyclooxygenase-2 by enflicoxib, its enantiomers and its main metabolites in vitro in canine blood

Enflicoxib is approved for the treatment of pain and inflammation in canine osteoarthritis. The objective of this work was to assess the mechanistic basis of enflicoxib therapy investigating the COX inhibitory activity of enflicoxib (racemate), its enantiomers and its main metabolites using the canine whole blood assay. The (R)‐(+)‐Enflicoxib enantiomer and metabolite M8 (hydroxylated pyrazoline) did not induce significant COX inhibition. Enflicoxib and its (S)‐(‐)‐Enflicoxib enantiomer inhibited COX‐1 and COX‐2 with variable degree of preferential isoform inhibition, but no significant therapeutic effect is anticipated in vivo. The pyrazol metabolite showed the highest COX‐2 inhibition and was the most selective (IC₅₀ COX‐1/ COX‐2 ratio: 19.45). As the pyrazol metabolite shows saturable binding to red blood cells, its in vivo concentrations in plasma are lower than in whole blood. Accordingly, when applying the red blood cell partitioning, the respective IC₅₀ and IC₈₀ for COX‐2 inhibition decreased from 2.8 µM (1129 ng/ml) and 13.4 µM (5404 ng/ml) to 0.2 µM (80.7 ng/ml) and 1.2 µM (484 ng/ml) and the selectivity ratio increased to close to 55. The corrected pyrazol metabolite IC₅₀ and IC₈₀ are well within the plasma levels described in treated dogs.

Pharmacology of enflicoxib, a new coxib drug: Efficacy and dose determination by clinical and pharmacokinetic-guided approach for the treatment of osteoarthritis in dogs based on an acute arthritis induction model

Enflicoxib is a newly developed NSAID of the coxib class. The optimal therapeutic dose to be confirmed in the field studies was established using a combination of pharmacokinetic (PK) modelling and pharmacodynamic (PD) studies. First, a PK study was performed to determine the plasmatic profile of enflicoxib and its active pyrazol metabolite in dogs. Thereafter, two studies using a urate crystal‐induced acute arthritis model allowed to correlate efficacy with plasmatic concentrations. Finally, a population PK model was developed to establish the Minimum Effective Concentration (MEC) and the Maximum Tolerated Concentration (MTC). Enflicoxib plasma concentrations were highest for the first 48 h. Thereafter, pyrazol metabolite concentrations were higher and persisted up to the end of the study. No reduction on the lameness (CLS) or pain scores (PS) was observed in the first hours after enflicoxib administration so no MEC could be established for the parent compound. Both CLS and PS were greatly reduced when the pyrazol metabolite achieved concentrations of 411 ng/ml or higher, so this concentration was established as the MEC for the pyrazol metabolite. Enflicoxib MTC was established at 6723 ng/ml whereas for the pyrazol metabolite it was 4258 ng/ml. The population PK model showed that a loading enflicoxib dose of 8 mg/kg followed by weekly maintenance doses of 4 mg/kg would achieve stable concentrations of the pyrazol metabolite within the therapeutic window (between the MEC and the MTC), and it was considered the most adequate posology to be confirmed in the field clinical studies for the treatment of canine osteoarthritis.

Efficacy and safety of enflicoxib for treatment of canine osteoarthritis: A 6-week randomised, controlled, blind, multicentre clinical trial

BACKGROUND

Enflicoxib is a new COX-2 selective NSAID intended for the treatment of pain and inflammation associated with canine osteoarthritis.

METHODS

A prospective, multisite, blinded, randomised, controlled, parallel-group field study was performed to determine the efficacy and safety of enflicoxib in canine osteoarthritis. A total of 242 dogs were randomised to receive enflicoxib at 4 or 2 mg/kg, mavacoxib at 2 mg/kg or placebo, orally. Enflicoxib and placebo were administered once weekly from day 0 to day 35. Mavacoxib was administered on D0 and day 14. Veterinarians assessed efficacy with a numerical rating scale and owners used the Canine Brief Pain Inventory.

RESULTS

After 6 weeks, enflicoxib at 4 mg/kg showed the highest percentage of responders as assessed by the veterinarians (68%) and the owners (84%), followed by mavacoxib (62and 83%, respectively), and enflicoxib at 2 mg/kg (57 and 80%, respectively). All treatments reached statistical significance versus placebo, which obtained success rates of 37% and 53%, respectively. No differences in the incidence of adverse reactions were detected among the different groups.

CONCLUSIONS

Enflicoxib administered weekly for 6 weeks, at 4 mg/kg PO with an initial loading dose of 8 mg/kg, is efficacious and safe for the treatment of canine osteoarthritis.

Pharmacokinetics of enflicoxib in dogs: Effects of prandial state and repeated administration

The pharmacokinetics of enflicoxib were evaluated in both a bioavailability study and a multi‐dose safety study in Beagle dogs. When administered at 8 mg/kg, the oral bioavailability (F) of enflicoxib was 44.1% in fasted dogs, but F increased to 63.4% under post prandial conditions. Enflicoxib is rapidly metabolised. After the first 48 h, the plasma levels of its pyrazol metabolite were much higher and persistent than those of the parent compound. Following intravenous administration, the total body plasma clearance of enflicoxib was of 140 ml/h/kg and the volume of distribution based on the terminal phase was 4 L/kg. Plasma protein binding for both compounds was approximately 99%. The blood to plasma ratio for the pyrazol metabolite showed saturable kinetics with higher blood cell affinity at lower total blood concentrations which ranged from 2.49 to 0.95 for concentrations from 1 to 15 µg/ml. Enflicoxib and its pyrazol metabolite exhibited dose‐proportional pharmacokinetics for single oral doses of 8–40 mg⁄kg and for multiple oral doses of 4–20 mg⁄kg. After 7 months of repeated weekly administrations, pre‐dose plasma concentrations (C_min,ss) remained constant throughout the study, with no trend to any significant over‐accumulation. The mean terminal elimination half‐life (t_½) was 20 h for enflicoxib and 17 days for the pyrazol metabolite. The pharmacokinetic profile of enflicoxib and its pyrazol metabolite in dogs supports the proposed dosing regimen in which doses are separated by 1 week.

PHARMACOKINETICS OF ORAL MAVACOXIB IN CARIBBEAN FLAMINGOS (PHOENICOPTERUS RUBER RUBER)

Mavacoxib is a selective cyclooxygenase-2 nonsteroidal anti-inflammatory drug that has been used for management of osteoarthritis and other inflammatory conditions in dogs. The main advantage of mavacoxib over other nonsteroidal anti-inflammatory drugs is its longer plasma half-life, leading to decreased dosing frequency. This study determined the pharmacokinetics of mavacoxib in Caribbean flamingos (Phoenicopterus ruber ruber) after a single-dose oral administration of 6 mg/kg (n = 6). Plasma mavacoxib concentrations were determined using liquid chromatography with mass spectrometry, and pharmacokinetic analysis was performed using noncompartmental methods. Mean peak plasma concentration (C_max) was (mean; range) 2.97 (2.19--4.06) µg/ml; mean time to peak plasma concentration (T_max) was 18.68 (4.00-48.00) hr; mean area under the curve (AUC) was 455 (292-637) hr * µg/ml; and mean terminal half-life (T_1/2) was 74.47 (49.57-161.43) hr. Based on the results of this study, mavacoxib dosed at 6 mg/kg orally in Caribbean flamingos reaches plasma concentrations above the therapeutic concentration established for dogs, but further studies are needed to determine appropriate dosing recommendations in flamingos.

Pedobarography: a novel approach to test the efficacy of treatments for lameness; an experience with mavacoxib in dogs with elbow osteoarthritis

Background

Pedobarographic analyses detect pressure redistribution among limbs and within limbs in humans, equids and dogs. The main objective of this study was to assess the usefulness of a set of pedobarographic parameters for the detection of lameness, as well as for its suitability for assessing the effects of therapies against osteoarthritis in dogs. With this purpose, eleven large-breed lame dogs with unilateral osteoarthritis due to elbow dysplasia were evaluated using a pressure platform prior to (D0) and after 3 months (D90) of treatment with mavacoxib, a COX-2 selective NSAID. The obtained parameters were: pressure distribution between lame and sound limbs, as well as paw area, mean pressure, and peak pressure of both lame and sound limbs.

Results

The results showed statistical differences in all these parameters between lame and sound limbs at D0; however, at D90, differences were significantly decreased as result of the treatment, indicating a substantial functional recovery under the study design conditions.

Conclusions

The provided data prove the suitability of this novel technique in canine models for the quantitative and objective assessment of lameness, but also for the evaluation of treatments for lameness caused by articular pain.

Electronic supplementary material

The online version of this article (10.1186/s12917-019-1946-1) contains supplementary material, which is available to authorized users.

Six-month safety evaluation of robenacoxib tablets (Onsior™) in dogs after daily oral administrations

Background

Robenacoxib is a non-steroidal anti-inflammatory drug available for canine and feline use for the control of pain and inflammation marketed as Onsior™. The aim of this target animal safety study was to evaluate the 6-month safety profile of oral robenacoxib administration. It was a randomized, negative-controlled, parallel group study. Thirty-two healthy, young, experimentally naïve, purebred Beagle dogs were administered 0 (sham control, Group 1), 2, 6, and 10 mg/kg robenacoxib (corresponding to the upper end of the dosage range [1X, Group 2] and multiples thereof [3X and 5X, Group 3 and 4]), orally once daily for 6 months. Assessment of safety included general health and clinical observations, physical, neurological, ophthalmological and electrocardiographic examinations, gross and histopathological examinations and clinical pathology evaluations. Blood samples were collected for toxicokinetic assessment of robenacoxib.

Results

No serious adverse events were reported. When compared with control, no treatment effect was observed for body weight, feed or water consumption, clinical pathology, urinalysis and fecal examination parameters. There were no treatment-related changes in stifle joint tissues and microscopic/histopathology examinations of all tissues/organs were normal. Salivation and soft feces were noted in all groups but observed more frequently in the treated groups as compared with control. On Day 178, increased buccal mucosal bleeding times were observed in two treated animals (Group 3 and 4) and one dog in Group 4 displayed a retinal change. Decreased hopping and conscious proprioception was noted in four treated dogs. One dog in Group 2 had ventricular premature complexes. Post-mortem changes included mild, red foci on the cecum in one dog (Group 3) and minimal duodenal discoloration in one dog (Group 4), with no corresponding histological findings in either dog. Ovarian weights were decreased in females from Group 3 and 4 with no gross or histological changes in the ovaries. Blood concentrations of robenacoxib confirmed systemic exposure of treated dogs. Exposure increased with increasing doses and there were no accumulation of robenacoxib in blood.

Conclusions

Robenacoxib was well tolerated at doses from 2 to 10 mg/kg/day and this 6-month study supports the safe use of Onsior™ (robenacoxib) tablets in dogs for the intended dosing regimen.

Comparative population pharmacokinetics and absolute oral bioavailability of COX-2 selective inhibitors celecoxib, mavacoxib and meloxicam in cockatiels (Nymphicus hollandicus)

Selective COX-2 inhibitors are non-steroidal anti-inflammatory drugs which directly target cyclooxygenase-2 (COX-2), an enzyme mainly responsible for induction of inflammation, pyresis and pain. Although commonly used in avian medicine, limited pharmacokinetic (PK) data in domestic and companion birds are available. In this study, PK parameters and absolute oral bioavailability expressed as percentage (F%) of celecoxib (10 mg/kg BW), mavacoxib (4 mg/kg BW) and meloxicam (1 mg/kg BW) were determined following single oral (PO) and intravenous (IV) administration to cockatiels (Nymphicus hollandicus). The drugs were quantified in plasma by liquid chromatography-tandem mass spectrometry. Data were processed using the nonlinear mixed effects (NLME) approach. In contrast to celecoxib (T_1/2el = 0.88 h) and meloxicam (T_1/2el = 0.90 h), mavacoxib has a prolonged elimination half-life (T_1/2el = 135 h) following oral administration of a commercial formulation (CF). High to complete oral absorption was observed following oral administration of celecoxib (F% = 56-110%) and mavacoxib (F% = 111-113%), CF and standard solutions, respectively. In contrast, the F% of meloxicam was low (F% = 11%). Based on the presented results, a less frequent dosing of mavacoxib is proposed compared to celecoxib and meloxicam. However, pharmacodynamic and safety studies are necessary to further investigate the use of these NSAIDs in cockatiels.

Comparison of veterinary drugs and veterinary homeopathy: part 2

Part 2 of this narrative review outlines the theoretical and practical bases for assessing the efficacy and effectiveness of conventional medicines and homeopathic products. Known and postulated mechanisms of action are critically reviewed. The evidence for clinical efficacy of products in both categories, in the form of practitioner experience, meta-analysis and systematic reviews of clinical trial results, is discussed. The review also addresses problems and pitfalls in assessing data, and the ethical and negative aspects of pharmacology and homeopathy in veterinary medicine.

Role of enterohepatic recirculation in drug disposition: cooperation and complications

Enterohepatic recirculation (EHC) concerns many physiological processes and notably affects pharmacokinetic parameters such as plasma half-life and AUC as well as estimates of bioavailability of drugs. Also, EHC plays a detrimental role as the compounds/drugs are allowed to recycle. An in-depth comprehension of this phenomenon and its consequences on the pharmacological effects of affected drugs is important and decisive in the design and development of new candidate drugs. EHC of a compound/drug occurs by biliary excretion and intestinal reabsorption, sometimes with hepatic conjugation and intestinal deconjugation. EHC leads to prolonged elimination half-life of the drugs, altered pharmacokinetics and pharmacodynamics. Study of the EHC of any drug is complicated due to unavailability of the apposite model, sophisticated procedures and ethical concerns. Different in vitro and in vivo methods for studies in experimental animals and humans have been devised, each having its own merits and demerits. Involvement of the different transporters in biliary excretion, intra- and inter-species, pathological and biochemical variabilities obscure the study of the phenomenon. Modeling of drugs undergoing EHC has always been intricate and exigent models have been exploited to interpret the pharmacokinetic profiles of drugs witnessing multiple peaks due to EHC. Here, we critically appraise the mechanisms of bile formation, factors affecting biliary drug elimination, methods to estimate biliary excretion of drugs, EHC, multiple peak phenomenon and its modeling.