Robenacoxib

BRAND NAMES

• Onsior – the primary brand name for both tablets and injectable forms for cats and dogs. 

• Onsior Injectable – specifically for veterinary injection use.

MECHANISM OF ACTION

Robenacoxib is a selective nonsteroidal anti-inflammatory drug (NSAID) that exerts its effects by specifically inhibiting the cyclooxygenase-2 (COX-2) enzyme, which is primarily responsible for producing prostaglandins involved in pain and inflammation. By targeting COX-2 while sparing COX-1, robenacoxib effectively reduces postoperative pain and inflammation in cats and dogs with a lower risk of gastrointestinal and renal side effects compared to non-selective NSAIDs. Its mechanism allows for precise control of inflammatory processes, providing analgesic and anti-inflammatory benefits in veterinary patients while maintaining the protective functions of COX-1.

PHARMACOKINETICS

Absorption

Robenacoxib is rapidly absorbed after oral or subcutaneous administration in cats and dogs, with peak plasma concentrations typically reached within 1 to 2 hours. Its absorption is not significantly affected by food, allowing flexibility in dosing. The drug exhibits good bioavailability, ensuring effective systemic exposure for managing postoperative pain and inflammation.

Distribution

Robenacoxib has a relatively low volume of distribution (Vd), reflecting its high plasma protein binding and limited penetration into non-inflamed tissues. This property allows the drug to remain largely in the circulation and preferentially reach inflamed sites, where it exerts its analgesic and anti-inflammatory effects, while minimizing systemic exposure and reducing the risk of adverse effects.

Metabolism

It is rapidly absorbed and metabolized in the liver through oxidation and conjugation, producing mostly inactive metabolites. These are mainly excreted in bile, with a small amount in urine. Despite a short plasma half-life, it remains effective at inflamed tissues, making it safe with minimal accumulation.

Elimination 

Robenacoxib is eliminated rapidly from the body, primarily through biliary excretion into feces, with a smaller proportion excreted via the urine. It has a short plasma half-life (about 1–2 hours), but due to its selective accumulation in inflamed tissues, its therapeutic effect lasts longer than its presence in plasma. The rapid elimination reduces the risk of drug accumulation and contributes to its overall safety profile.

PHARMACODYNAMICS

Robenacoxib is a selective COX-2 inhibitor that works by blocking the cyclooxygenase-2 (COX-2) enzyme responsible for producing prostaglandins involved in pain and inflammation. By selectively inhibiting COX-2 while sparing COX-1, it reduces inflammation, pain, and fever with fewer gastrointestinal and renal side effects. It also shows preferential action at inflamed tissues, enhancing its therapeutic effectiveness.

ADMINISTRATION

Robenacoxib is administered primarily by the oral route as tablets, and it is also available as an injectable formulation for subcutaneous use in veterinary practice. It is usually given once daily, with or without food depending on the formulation and species. The dosage and duration depend on the animal (commonly dogs and cats) and the condition being treated, such as postoperative pain or inflammation.

DOSAGE AND STRENGTH

Robenacoxib is given once daily, with doses of 1–2 mg/kg in dogs and about 1 mg/kg in cats. It is available in tablet strengths of 5 mg, 10 mg, 20 mg, and 40 mg, as well as injectable forms.

DRUG INTERACTIONS

Robenacoxib should not be used with other NSAIDs or corticosteroids due to increased risk of toxicity. Caution is needed with diuretics, ACE inhibitors, and other protein-bound drugs, as they may increase the risk of kidney damage or side effects.

FOOD INTERACTIONS

Robenacoxib can be given with or without food, but food may slightly reduce its absorption rate. However, this does not significantly affect its overall effectiveness, and administering it with food may help reduce the risk of gastrointestinal irritation.

CONTRAINDICATIONS

Robenacoxib should not be used in animals with hypersensitivity to NSAIDs, active ulcers, severe liver or kidney disease, or in pregnant and lactating animals. It is also contraindicated with other NSAIDs or corticosteroids.

SIDE EFFECTS

• Vomiting and diarrhea 

• Loss of appetite 

• Lethargy or weakness 

• Gastrointestinal ulcers or bleeding 

• Kidney or liver function abnormalities 

• Rare allergic reactions (swelling, itching, hives)

OVER DOSE

Overdose may cause vomiting, diarrhea, lethargy, or kidney and liver problems. Treatment is supportive with fluids, gastric protection, and veterinary monitoring.

TOXICITY

Robenacoxib toxicity is rare but can occur with overdose or prolonged use. It may lead to gastrointestinal ulcers, kidney or liver damage, vomiting, diarrhea, and lethargy. Early detection and supportive veterinary care, including fluids and gastric protection, are essential to prevent serious complications.