Robenacoxib (Onsior) for Pain and Inflammation in Dogs and Cats

Bottom line

• Robenacoxib (Onsior) is a coxib-class NSAID with exceptionally high COX-2 selectivity: in cats, the COX-1:COX-2 IC50 ratio is 502.3, and at 95% COX-2 inhibition only 12.4% of COX-1 is inhibited. [1]
• The drug achieves tissue-selective anti-inflammatory activity by preferentially distributing into and persisting in inflammatory exudate while rapidly clearing from blood, potentially reducing systemic COX-1-mediated adverse effects. [1]
• In European field trials, robenacoxib produced noninferior analgesia to meloxicam and carprofen for acute and chronic musculoskeletal pain in dogs and cats. [1]
• In cats, perioperative subcutaneous robenacoxib showed superior analgesia to meloxicam after soft tissue and orthopaedic surgeries. [1]
• Approved for cats (EMA) for pain and inflammation associated with acute/chronic musculoskeletal disorders and for reduction of moderate pain and inflammation associated with orthopaedic surgery. [2]

Drug facts

• Class: NSAID, coxib-class (selective COX-2 inhibitor)
• Mechanism: Highly selective and targeted inhibition of COX-2; weak and rapidly reversible binding to COX-1; preferential distribution into inflammatory exudate
• Route/interval: Oral tablet or subcutaneous injection; frequency per label
• Indication (cats): Treatment of pain and inflammation associated with acute or chronic musculoskeletal disorders; reduction of moderate pain and inflammation associated with orthopaedic surgery [2]
• Indication (dogs): Treatment of pain and inflammation associated with musculoskeletal disorders including osteoarthritis; perioperative pain management
• Approval: EMA first authorised (cats oral) with subsequent extensions; marketed as Onsior by Elanco
• Label contraindications: Gastrointestinal ulceration; concomitant NSAIDs or corticosteroids; hypersensitivity to active substance; do not use in pregnant or lactating animals [2]
• Label common AEs: Vomiting, soft faeces; generally mild and consistent with NSAID class; no clinically significant renal, hepatic, or haematological toxicity at recommended doses [2]

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What the evidence shows

COX selectivity: the pharmacological basis

Robenacoxib was developed from the premise that COX-2 selectivity combined with tissue-level concentration at sites of inflammation would deliver effective analgesia with a wide safety margin. In feline whole blood assays, the mean IC50 values were 0.058 micromolar for COX-2 and 28.9 micromolar for COX-1 — a COX-1:COX-2 IC50 ratio of 502.3. At the level of 95% COX-2 inhibition, robenacoxib produced only 12.4% inhibition of COX-1, compared with 72.7% COX-1 inhibition for meloxicam and near-complete COX-1 inhibition for ketoprofen at comparable COX-2 inhibition levels.

In canine whole blood assays, robenacoxib ranked highest in COX-2 inhibition potency among the NSAIDs tested. At clinically recommended doses, robenacoxib significantly inhibited COX-2 (measured as ex vivo PGE2 levels) without markedly affecting COX-1 (measured as serum TXB2) in acute synovitis models. [1]

Tissue selectivity and pharmacokinetics

A key characteristic of robenacoxib is its acidic moiety and high plasma protein binding (>98%). This drives preferential distribution into protein-rich inflammatory exudate at sites of inflammation, while rapid plasma clearance (mean terminal blood half-life approximately 0.6-0.9 hours in dogs; 1.87 hours in cats) limits systemic exposure. In feline tissue cage inflammation models, the mean residence time in inflammatory exudate was approximately 24 hours regardless of route, far exceeding the blood residence time. This pharmacokinetic profile explains why a once-daily dosing regimen produces sustained anti-inflammatory effects despite brief blood concentrations. [1]

Clinical trials in cats

Large multicentre randomised field trials in Europe (n=155) and Japan (n=68) compared oral robenacoxib with ketoprofen as an active control for acute musculoskeletal pain in cats. Robenacoxib produced noninferior efficacy and tolerability to ketoprofen by investigator and owner assessment, with no significant differences in haematology, clinical chemistry, or urinalysis parameters.

Perioperative studies established a clearer efficacy signal: preoperative subcutaneous robenacoxib showed superior efficacy to subcutaneous meloxicam in reducing pain scores for 22 hours after soft tissue and orthopaedic surgeries in a multicentre randomised clinical trial, with no adverse clinical signs in either group.

Long-term administration of oral robenacoxib in cats with osteoarthritis and concurrent chronic kidney disease showed no clinically detected evidence of damage to the gastrointestinal tract, liver, or kidney. [1]

Clinical trials in dogs

For perioperative pain in dogs undergoing soft tissue or orthopaedic surgery, two large separate multicentre randomised blinded field trials found no significant differences in pain scores between robenacoxib and meloxicam (active control) when assessed by veterinary investigators using the Glasgow pain scale or by owners. No dogs required rescue analgesia.

For canine osteoarthritis, robenacoxib produced noninferior efficacy to carprofen for pain and functional disability scores over 12 weeks, the standard comparator for this indication. An additional Japanese trial confirmed similar noninferiority and tolerability in local dog breeds. The tissue-selective anti-inflammatory activity of robenacoxib in canine OA was demonstrated by a significant reduction in synovial fluid CRP at 28 days, without a change in serum CRP, consistent with the drug's preferential distribution to the inflammatory exudate. [1]

How this fits clinical practice

Robenacoxib occupies a useful position in species where renal, gastrointestinal, or cardiovascular concerns raise the COX-1 safety threshold, particularly in cats. Its tissue-selective distribution pattern and rapid blood clearance make it distinctly different from less COX-2-selective NSAIDs, especially for patients requiring concurrent drugs affecting renal haemodynamics, though concurrent use with other NSAIDs or corticosteroids remains contraindicated. For cats with concurrent CKD and osteoarthritis, the clinical safety evidence at recommended doses provides reassurance, while the label still advises individual assessment and monitoring. Confirm all dosing and duration decisions with current formularies and product labelling.

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References

1. Kongara K, Chambers JP. Robenacoxib in the treatment of pain in cats and dogs: safety, efficacy, and place in therapy. Vet Med (Auckl). 2018;9:53-61. https://www.dovepress.com/article/download/39891
2. Elanco. Onsior 6 mg tablets for cats — Summary of Product Characteristics (Annex I). European Commission community register; 2018. https://ec.europa.eu/health/documents/community-register/2018/20180426140601/anx_140601_en.pdf

Changelog

• 2026-06-07: First published.