Canine osteoarthritis (OA) is an important disease of the dog. Prevalence rates can range from between 2.5%¹ to nearly 40%², meaning potentially millions of dogs may be affected in the UK each year.

Even young dogs (8 months to 4 years) can be significantly affected by this disease process with a prevalence rate of 23% in one study; and of the dogs with radiographic evidence of OA showing clinical signs, many were not yet receiving treatment³.

NSAIDs have been a bedrock of the management of OA for decades and have a reputation for effectiveness in providing anti-inflammatory action and potent analgesia.

However, long term use is overshadowed by concerns about the potential for induction of suspected adverse events (SAEs), prompting avoidance strategies, and therefore consequences to patient, owner, and the vet practice.

OA: disease characteristics

OA, in both human and animal species, is characterised primarily by a loss of articular cartilage, causing pain, and progressive joint and limb dysfunction.

Secondary OA is thought to be the most common form of the disease, often developing as a sequel to underlying genetic predispositions or injuries⁴. It is classified as an inflammatory condition, with upregulation of inflammatory mediators, cytokines, proteases and enzymes within the joint space, often being referred to as “inflammatory soup”. Progression of disease can be insidious and regular monitoring and staging of disease are important to apply appropriate therapeutic interventions at the appropriate time.

Prostaglandin E₂  (PGE₂) is associated with inflammatory conditions, being produced as a result, through the arachidonic acid pathway upon further cell damage due to inflammatory responses, catalysed by both isoforms of cyclooxygenase (COX). COX inhibition leads to PGE₂ suppression, thereby inhibiting the inflammatory cascade, as well as reducing associated pain⁵.

NSAIDs are a group of compounds that inhibit COX enzymes.

Safety of NSAIDs in literature

NSAIDs are the most widely used analgesic in veterinary medicine⁶. They have an excellent safety profile when the number of doses administered to animals each year are considered.

They are, however, associated with a variety of potential adverse events through their inhibition of both COX-isoforms, which can include GI irritation, hepatic and renal toxicity, and coagulation disorders⁶.

In one systematic review, the most common SAEs across studies were GI disturbances, specifically vomiting, diarrhoea and anorexia⁷.

The most recent analysis of SAEs⁸ relating to NSAID use suggests that the overall frequency is low, with a similar frequency between molecules examined.

Injectable formulations were associated with a higher frequency of reported SAEs, which may be due to their use in the peri-operative period. The rate of emesis in this review was less than one report per 500 doses sold, and was noted in the top five reported SAEs alongside anorexia and diarrhoea.

A study focusing on enflicoxib use across a six-month period⁹ crucially noted that SAEs decreased over time (highest within the first eight weeks), and that treatment duration was unrelated to an increased risk of SAEs, confirming observations of Innes et al¹⁰.

Ultimately, within the currently available literature, the balance of evidence suggests that for dogs with chronic OA receiving NSAIDs, the risk of serious SAEs is low^7,8,10.

Vet and owner

In a recent clinician-based survey in the UK¹¹, OA was voted the most common cause of chronic pain in dogs attending UK practices.

The most common barriers to initiating appropriate analgesia/treatment in all cases of chronic pain included difficulties in assessing canine pain, compliance with treatment plans and potential for adverse events. Based on this survey, clinician education and support in these areas could improve the long-term management of OA.

A 2016 survey¹² suggested that both clinicians and pet owners alike have high levels of awareness for the risk of problems relating to NSAID therapy. This concern from both parties has the potential to affect not only the prescription of NSAIDs to patients that could benefit from them, but also could affect the likelihood of the pet owner continuing with the therapy.

The situation is further complicated by differing opinions among clinicians and pet owners on the long-term use of NSAIDs. Strategies like “off-label” dose reduction and alternate-day dosing do occur, but there is no evidence to support these approaches.

Significant consequences of “off-label” use of NSAIDs in OA cases could involve not only the deteriorating welfare of the patient over the long-term, but the confidence of the pet owner in proposed treatment plans, owner trust in adaptation of treatment plans and potentially loss of business through loss of owner confidence.

Owners may feel disengaged with a particular clinician, or the practice as a whole.

Canine OA treatment pathway

The long-term benefit of NSAID use in canine OA has previously been described in the available literature¹⁰. The need to prevent/reduce central sensitisation, provide sufficient analgesia, reduce inflammation and maintain joint functionality are the key elements of any multi-modal approach to OA therapy.

In 2023, a treatment pathway for all stages of OA, including a diagnostic staging tool were launched on to the market. The canine osteoarthritis staging tool (COAST) – and subsequent international consensus guidelines¹³ – are intended to support clinicians in their OA treatment plan implementation once diagnosis has been made. Contextualised care is at the heart of the guidelines. In a recent 2023 survey by Animalcare UK, it was found that weekly administration of OA treatment was preferred by 72% of respondents¹⁴.

Many canine OA patients may present later in life, and in a more advanced stage of OA. The COAST guidelines recommend that for stage 4 (severe) OA, a minimum of 12 weeks of therapy should be initiated, but that NSAID cessation is unlikely in this stage of disease.

Suggestion is also made that if a SAE occurs with one NSAID, where possible, and at the clinicians discretion, therapy should be continued with another NSAID, taking into consideration appropriate wash-out periods – currently 5 to 7 days for NSAIDs⁶ – between products with alternative analgesia utilised if appropriate in the switch over period.

NSAIDS have a strong enduring evidence base as a drug class for use in the management of canine OA, with SAEs commonly being transient and self-limiting. NSAIDs can be used in both short-term and long-term management and should be considered as a good first-line therapeutic option.