Onsior (Robenacoxib) — Veterinary Vademecum Drug Reference

Dosage & Administration Guidelines

Species	Route	Dose	Frequency	Duration & Clinical Notes
Dog	PO	1-2 mg/kg	q24h	Duration: For osteoarthritis: up to 6 months; for post-operative pain: 3-7 days Notes: Administer with food to enhance absorption. For post-operative pain, administer 1-2 hours before surgery or at the time of induction.
Cat	PO	1-2.4 mg/kg	q24h	Duration: For musculoskeletal pain: up to 6 months; for post-operative pain: 3-5 days Notes: Administer with food. For post-operative pain, administer 1-2 hours before surgery or at the time of induction.
Horse	IV	0.5-1 mg/kg	q24h	Duration: Up to 5 days Notes: Not approved in all countries; use under veterinary discretion. For acute pain management.

Clinical Indications & Species Uses

General Indications

Management of acute and chronic pain and inflammation in dogs and cats

Dog (Canine)

Pain and inflammation associated with osteoarthritis
Post-operative pain and inflammation following orthopedic and soft tissue surgery

Cat (Feline)

Pain and inflammation associated with musculoskeletal disorders (e.g., osteoarthritis)
Post-operative pain and inflammation following ovariohysterectomy, castration, and soft tissue surgery

Horse (Equine)

Pain and inflammation associated with acute musculoskeletal disorders (e.g., colic, laminitis) - not approved in all countries

Pharmacology & Mechanism of Action

Drug Class: Nonsteroidal Anti-inflammatory Drug (NSAID) | Pharmacological Group: Coxib (selective COX-2 inhibitor)

Mechanism of Action: Robenacoxib is a nonsteroidal anti-inflammatory drug (NSAID) that selectively inhibits cyclooxygenase-2 (COX-2) over cyclooxygenase-1 (COX-1). By selectively blocking COX-2, robenacoxib reduces the synthesis of pro-inflammatory prostaglandins (e.g., PGE2) at sites of inflammation while sparing COX-1-derived prostaglandins that are important for gastrointestinal mucosal protection, renal blood flow, and platelet function. This selectivity is dose-dependent and species-specific, with higher selectivity in cats and dogs compared to other NSAIDs. The anti-inflammatory, analgesic, and antipyretic effects are mediated through this inhibition of prostaglandin synthesis.

Pharmacodynamics: Robenacoxib exhibits potent anti-inflammatory, analgesic, and antipyretic activity. In animal models, it has been shown to reduce inflammation and pain associated with acute and chronic musculoskeletal disorders. Its COX-2 selectivity is high, with a selectivity ratio (COX-1/COX-2) of approximately 100-fold in dogs and cats, which contributes to a favorable gastrointestinal safety profile compared to non-selective NSAIDs. The onset of analgesia occurs within 1-2 hours after oral administration, and the duration of action supports once-daily dosing. Robenacoxib also has a long duration of action in cats, allowing for extended dosing intervals in some cases.

⚡ Pharmacokinetics Summary

Absorption: Robenacoxib is well absorbed after oral administration in dogs and cats. In dogs, oral bioavailability is approximately 70-80% when given with food, but may be reduced when given on an empty stomach. In cats, oral bioavailability is approximately 50-60% and is also affected by food. Peak plasma concentrations are reached within 1-2 hours in dogs and 1-3 hours in cats. In horses, oral absorption is variable, and the drug is often administered intravenously for acute pain management.

Distribution: Robenacoxib is highly protein-bound (>99%) in plasma, primarily to albumin. It distributes widely into tissues, with high concentrations found in inflammatory exudate, synovial fluid, and other target tissues. The volume of distribution is relatively small, consistent with its high protein binding. In cats, the drug accumulates in inflamed tissues, contributing to its prolonged duration of action.

Metabolism: Robenacoxib is extensively metabolized in the liver, primarily via hydroxylation and conjugation. The major metabolic pathways involve cytochrome P450 enzymes (CYP) and glucuronidation. In dogs, the primary metabolites are hydroxylated derivatives, while in cats, glucuronide conjugates are more prominent. The metabolism is species-specific, and the drug does not undergo significant enterohepatic recirculation.

Excretion: Robenacoxib is eliminated primarily via the biliary route, with a significant portion excreted in feces. Renal excretion is a minor pathway, with less than 10% of the dose recovered in urine. The elimination half-life is approximately 1-2 hours in dogs and 1-3 hours in cats, but the pharmacodynamic effect lasts longer due to tissue distribution. In horses, the half-life is approximately 1-2 hours after intravenous administration.

Half-Life: Dog: 1-2 hours; Cat: 1-3 hours; Horse: 1-2 hours (IV)

Bioavailability: Dog: ~70-80% (with food); Cat: ~50-60% (with food); Horse: variable after oral administration

Protein Binding: >99% (primarily to albumin)

Available Formulations & Strengths

Oral Tablet 5 mg, 10 mg, 20 mg, 40 mg (PO)

Injectable Solution 20 mg/mL (SC or IV)

Contraindications & Clinical Warnings

Contraindications:

Hypersensitivity to robenacoxib or any other NSAID
Gastrointestinal ulceration or bleeding
Renal or hepatic impairment
Dehydration, hypovolemia, or hypotension
Concurrent use of other NSAIDs or corticosteroids
Pregnancy or lactation (unless specifically indicated by a veterinarian)
Use in animals less than 10 weeks of age (safety not established)

Warnings & Clinical Precautions:

Use with caution in animals with pre-existing renal, hepatic, or cardiac disease.
Monitor for signs of gastrointestinal toxicity (vomiting, diarrhea, melena) during therapy.
In cats, long-term use may be associated with renal toxicity; monitor renal function periodically.
Do not exceed the recommended dose or duration.
Administer with food to reduce gastrointestinal upset.
In horses, use only when approved and under veterinary supervision.
Avoid use in animals that are dehydrated, hypovolemic, or hypotensive.
Safety in breeding, pregnant, or lactating animals has not been fully established.

Adverse Effects & Reactions

Common:

Vomiting
Diarrhea
Decreased appetite
Lethargy

Serious / Severe:

Gastrointestinal ulceration or perforation
Renal toxicity (acute renal failure)
Hepatic toxicity
Bleeding disorders

Rare:

Allergic reactions (skin rash, anaphylaxis)
Neurological signs (ataxia, seizures)
Blood dyscrasias

Key Drug Interactions

Interacting Drug / Class	Clinical Effect & Mechanism	Severity
Other NSAIDs (e.g., carprofen, meloxicam)	Increased risk of gastrointestinal ulceration and renal toxicity	High
Corticosteroids (e.g., prednisone, dexamethasone)	Increased risk of gastrointestinal ulceration and renal toxicity	High
Anticoagulants (e.g., warfarin, heparin)	Increased risk of bleeding	Moderate
ACE inhibitors (e.g., enalapril, benazepril)	Reduced renal function and increased risk of renal toxicity	Moderate
Diuretics (e.g., furosemide)	Increased risk of renal toxicity and reduced diuretic efficacy	Moderate
Aminoglycoside antibiotics	Increased risk of renal toxicity	Moderate

Overdose & Toxicity Management

Signs of Toxicity:

Vomiting
Diarrhea (possibly with blood)
Lethargy
Loss of appetite
Abdominal pain
Renal failure (in severe cases)
Seizures (in extreme cases)

Emergency Treatment Protocol: Treatment of overdose is symptomatic and supportive. Induce vomiting if ingestion is recent (within 2 hours) and the animal is conscious. Administer activated charcoal to reduce absorption. Provide intravenous fluids to maintain renal perfusion and correct dehydration. Monitor renal and hepatic function. Use gastroprotective agents (e.g., sucralfate, H2 antagonists, proton pump inhibitors) if gastrointestinal signs occur. In severe cases, consider hemodialysis or peritoneal dialysis. There is no specific antidote for robenacoxib overdose.

Food Animal Withdrawal Times

Robenacoxib is not approved for use in food-producing animals in most countries. Therefore, withdrawal times are not established. If used off-label in food animals, consult regulatory guidelines and ensure adequate withdrawal periods to avoid residues.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature 20-25°C (68-77°F), with excursions permitted between 15-30°C (59-86°F).

Handling & Special Conditions: Protect from moisture. Keep in original container. Do not remove desiccant.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Approved by FDA for use in dogs and cats (Onsior).

Extra-Label (Off-Label) Use: In the US, robenacoxib is approved for use in dogs and cats. Extra-label use in other species or for other indications must comply with AMDUCA regulations. In the EU, robenacoxib is approved for use in dogs and cats, and in some countries for horses. Use in food-producing animals is prohibited or requires a long withdrawal period.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Robenacoxib (Onsior) is a highly selective COX-2 inhibitor NSAID used primarily in dogs and cats for the management of acute and chronic pain and inflammation. It is particularly useful for post-operative pain control and osteoarthritis. Its selectivity for COX-2 provides a favorable safety profile compared to non-selective NSAIDs, but it is not without risks. Clinicians should use the lowest effective dose for the shortest duration necessary. Administer with food to enhance absorption and reduce gastrointestinal upset. Monitor renal and hepatic function in animals on long-term therapy, especially in cats. Avoid concurrent use with other NSAIDs or corticosteroids. In horses, robenacoxib is used off-label in some countries for acute pain; however, its use is not universally approved. Always follow label instructions and local regulations. For food animals, robenacoxib is not approved, and extra-label use is discouraged due to lack of withdrawal data.

References & Literature

📚 Plumb's Veterinary Drug Handbook
📚 Papich Veterinary Pharmacology and Therapeutics
📚 Compendium of Veterinary Products (CVP)