ATCvet code: QM01AH91.

Robenacoxib is a non-steroidal anti-inflammatory drug (NSAID) of the coxib class. It is a potent and selective inhibitor of the cyclooxygenase 2 enzyme (COX-2). The cyclooxygenase enzyme (COX) is present in two forms. COX-1 is the constitutive form of the enzyme and has protective functions, e.g. in the gastrointestinal tract and kidneys. COX-2 is the inducible form of the enzyme and is responsible for the production of mediators including PGE2 which induce pain, inflammation or fever.

In cats, using an in vitro whole blood assay, robenacoxib was approximately 500 fold selective for COX-2 (IC50 0.058 μM) as compared to COX-1 (IC50 28.9 μM). In vivo, robenacoxib solution for injection produced marked inhibition of COX-2 activity and had no effect on COX-1 activity. At the recommended dosage (2 mg/kg), analgesic, anti-inflammatory and anti-pyretic effects were demonstrated in an inflammation model, and in clinical trials, robenacoxib reduced pain and inflammation in cats undergoing orthopaedic or soft tissue surgery.

In dogs, robenacoxib was in vitro approximately 140 fold selective for COX-2 (IC50 0.04 μM) as compared to COX-1 (IC50 7.9 μM). In vivo, robenacoxib solution for injection produced marked inhibition of COX-2 activity and had no effect on COX-1 activity. At dosages ranging from 0.25 to 4 mg/kg, robenacoxib had analgesic, anti-inflammatory and anti-pyretic effects in an inflammation model with a rapid onset of action (1 h). In clinical trials at the recommended dose (2 mg/kg), robenacoxib reduced pain and inflammation in dogs undergoing orthopaedic or soft tissue surgery, and reduced the need for rescue treatment in dogs undergoing soft tissue surgery

Peak blood concentrations of robenacoxib are attained rapidly after subcutaneous injection in cats and dogs. After a dosage of 2 mg/kg a Tmax of 1 h (cats and dogs), a Cmax of 1,464 ng/ml (cats) and 615 ng/ml (dogs), and an AUC of 3,128 ng·h/ml (cats) and 2,180 ng·h/ml (dogs) is obtained. After a subcutaneous administration of 1 mg/kg the systemic bioavailability is 69% in cats and 88% in dogs.

Robenacoxib has a relatively small volume of distribution (Vss of 190 ml/kg in cats and 240 ml/kg in dogs) and is highly bound to plasma proteins (>99%).

Robenacoxib is extensively metabolised by the liver in cats and dogs. Apart from one lactam metabolite, the identity of other metabolites is not known in cats or dogs.

After intravenous administration robenacoxib was rapidly cleared from blood (CL of 0.44 L/kg/h in cats and 0.81 L/kg/h in dogs) with an elimination t1/2 of 1.1 h in cats and 0.8 h in dogs.After subcutaneous administration, the terminal half-life from blood was 1.1 h in cats and 1.2 h in dogs. Robenacoxib persists longer and in higher concentrations at sites of inflammation than in blood. Robenacoxib is excreted predominantly via the biliary route in cats (around 70%) and dogs (around 65%) and the remainder via the kidneys. Repeated subcutaneous administration at dosages of 2–20 mg/kg produced no change in the blood profile, with neither bioaccumulation of robenacoxib nor enzyme induction. Bioaccumulation of metabolites has not been tested. The pharmacokinetics of robenacoxib injection do not differ between male and female cats and dogs, and are linear over the range of 0.25–4 mg/kg in dogs.