Long-term safety evaluation of Daxocox® tablets (enflicoxib) in dogs after weekly oral administrations for seven months

A blinded, randomized and controlled multicenter field study investigating the safety and efficacy of long-term use of enflicoxib in the treatment of naturally occurring osteoarthritis in client-owned dogs

Background

Enflicoxib is a COX-2 selective NSAID shown to be efficacious and safe in the treatment of pain and inflammation associated with canine osteoarthritis (OA) in clinical studies of 6 weeks duration.

Objective

This prospective, multisite, blinded, randomized, placebo-controlled, parallel-group field study aimed to confirm the safety and efficacy of enflicoxib in long-term canine OA treatments.

Animals

A total of 109 client owned dogs with clinical and radiographic signs of OA for at least 3 weeks were enrolled with 78 dogs completing all study visits.

Methods

Dogs were randomized at a 3:1 ratio to receive enflicoxib (n = 83) or placebo (n = 26) once weekly during 6 months. Dogs underwent veterinary assessments from Day 0 to Day 189 using a clinical sum score (CSS). Efficacy was also assessed by the owners using the Canine Brief Pain Inventory (CBPI). Safety was assessed clinically and by repeated blood and urine sample analysis. The efficacy outcome measure was the treatment response according to the CSS and secondarily the treatment response according to the CBPI. The primary safety outcome was the incidence of adverse events (AEs) and secondarily the evolution of the clinical pathology parameters.

Results

Percentages of CSS responders for enflicoxib were 71.6; 74.6 and 71.6% on Days 44, 135 and 189 respectively, always showing statistically significant differences (p < 0.05) vs. placebo (41.7, 33.3, and 20.8% respectively). Treatment response according to owner assessments followed the same pattern, achieving significant differences compared to placebo after 2 weeks of treatment. The incidence and type of AEs were as described in previous enflicoxib studies of shorter duration and as for other NSAIDs, with no tendency to increase over time. No relevant changes in hematology, biochemistry or urine parameters were observed.

Conclusions and clinical relevance

Enflicoxib safety and efficacy profile is maintained after a long-term treatment, which together with its weekly administration, makes it a good alternative for the chronic treatment of dogs with naturally occurring OA.

[New drugs for small animals in 2021]

In 2021, 8 novel pharmaceutical agents for small animals were released on the German market: The specific monoclonal antibodies bedinvetmab (Librela^®) and frunevetmab (Solensia^®), the cyclooxygenase-2 inhibitor enflioxib (Daxocox^®), the ectoparasitic esafoxolaner (NexGard^® Combo) of the isoxazoline group, the anti-haemorrhagic etamsylate (Hemosilate), the antidepressant mirtazapine (Mirataz^®), the alpha-selective sympathomimetic tetryzoline for ophthalmic use (Zolicep^®) and the cytostatic tigilanol tiglate (Stelfonta^®). No active substance received an animal species extension. In addition, for small animals, there were new releases of two agents in a novel pharmaceutical formulation (cefalexin, gentamicin), five drugs with a new content of the active ingredient (metronidazole, pimobendan, thiamazole, tramadol, trilostane), one veterinary drug with a new combination of active ingredients (lotilaner + milbemycin oxime), one drug with a new route of administration (propofol) and furthermore two temporarily non-available active ingredients for certain animal species were reapproved in new drugs (levothyroxine for cats and oxytetracycline for dogs and cats).

Evaluation of the Genotoxic Potential of the Selective COX-2 Inhibitor Enflicoxib in a Battery of in vitro and in vivo Genotoxicity Assays

Aim Enflicoxib, a selective COX-2 inhibitor approved for the treatment of pain and inflammation associated with osteoarthritis in dogs (Daxocox ^® [Ecuphar/Animalcare Group]) was assessed for its genotoxic potential in a battery of in vitro and in vivo genotoxicity assays. These comprised a bacterial reverse mutation assay (Ames test), an in vitro human lymphocyte chromosome aberration assay and an in vivo mouse bone marrow micronucleus assay.

Methods Relevant vehicle and positive control cultures and animals were included in all assays. In the Ames test, enflicoxib was tested at concentrations of up to 5000 μg/plate. Signs of cytotoxicity were observed at the highest tested concentrations for several of the bacterial strains, both in absence and presence of S9. In human lymphocytes, enflicoxib was assessed for the induction of chromosomal aberrations when exposed at concentrations of up to 62.5 (3 hours) and 29.6 µg/mL (20 hours) in the absence of S9, and up to 66.7 µg/mL (3 hours) in presence of S9. Signs of cell toxicity, evidenced as a decrease in the mitotic index, were observed at these concentrations. In the mouse micronucleus assay, enflicoxib dose levels of up to 2000 mg/kg were administered (single dose) to male and female animals, and bone marrow samples were taken 24 and 48 hours (high-dose animals only) after administration.

Results Enflicoxib was shown to lack genotoxic activity in the conducted assays.

Conclusions The administration of enflicoxib as a therapeutic analgesic agent would not pose a genotoxic risk to animals or humans.

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.