Though chronic pain can be difficult to diagnose and assess, there are several validated pain scales for osteoarthritis and quality of life assessments that can be used to guide treatment. So, once we have identified whether our patient’s pain is acute, chronic (nociceptive) or osteoarthritic, the next stage is to create an appropriate treatment plan. But how do we do this? What should we include, and what needs to be considered?
How should I approach the case?
How should I approach the case? Although management of the underlying condition is always a priority, in terms of pain management the author considers four main components (Table 1) when formulating a treatment plan for cases of osteoarthritis (OA) chronic pain.
It is vital to manage the owner’s expectations and ensure they are involved in the decision-making process. Many chronic pain patients will face their disease for life and require continuous treatment, which involves associated care and financial commitments from the owner.
| Lifestyle management | Nutrition and adjuncts | “Licensed” pharmacotherapy | “Unlicensed” pharmacotherapy |
|---|---|---|---|
| Weight control Exercise Physical therapies Acupuncture | Functional foods Nutraceuticals Disease-modifying osteoarthritis drugs (DMOADs) | Non-steroidal anti-inflammatory drugs (NSAIDs) Paracetamol/codeine Monoclonal antibodies | Amantadine Tapentadol Gabapentin Pregablin Amitriptyline |
Current and developing pharmacological treatments for chronic pain in companion animals
Licensed agents
Non-steroidal anti-inflammatory drugs (NSAIDs) are the most-prescribed licensed medication for treating chronic pain in companion animals. It is the author’s belief that they should be used wherever possible due to their good analgesic and anti-inflammatory effects. Grapiprant (Galliprant) is a novel NSAID of the piprant class which acts via antagonism of prostaglandins at the EP4 receptor, the primary mediator of canine OA pain (Kirkby-Shaw et al., 2016). Therefore, in theory, these should not interfere with the homeostatic mechanisms mediated by constitutive prostaglandins.
Non-steroidal anti-inflammatory drugs (NSAIDs) are the most-prescribed licensed medication for treating chronic pain in companion animals
Despite a lack of clinical trials, paracetamol appears to provide appropriate analgesia for chronic pain conditions when administered at appropriate doses in dogs, in the author’s experience. However, paracetamol should be avoided in cats. “Pardale” is a licensed form of paracetamol that also contains codeine.
More recently, monoclonal antibody (mAb) therapies targeting chronic pain and species-specific anti-nerve growth factor (anti-NGF) have been developed for OA-associated pain in dogs and cats. Early clinical trials have shown that anti-NGF therapy appears very effective (Enomoto et al., 2019). Subsequently, Zoetis has released Librela (bedinvetmab) for dogs and Solensia (frunevetmab) for cats, both administered by monthly injection. Early clinical experience with these agents has been very positive, and studies are now being published showing how these agents perform in clinical OA cases presented to veterinary surgeons (Michels et al., 2023).
Unlicensed agents used under the prescribing cascade
Gabapentin and pregablin have traditionally been used for the treatment of neuropathic pain, but they are useful adjuncts in the management of chronic pain. However, the side effects include sedation, particularly when treatment is started.
Amantadine works in the same way as ketamine – via N-methyl D-aspartate receptor (NMDA) antagonism – and is often used in conjunction with NSAIDs in dogs with chronic osteoarthritis pain refractory to NSAIDs alone (Lascelles et al.,2008). Various doses have been reported, but the author tends to use them as a starting point, increasing as necessary. Occasionally, clinicians will split the dose of amantadine every 12 hours, which appears to give better pain control in some cases. Amantadine has also been used in cats. The biggest side effect is nausea, but some authors have advocated use of another NMDA antagonist, memantine, to overcome this problem.
Amitriptyline is a tricyclic antidepressant used for controlling neuropathic pain in humans. It has been used to treat neuropathic pain in dogs when given at a low dose, but should not be used with tramadol or other drugs that inhibit serotonin and norepinephrine uptake.
Tramadol is an atypical synthetic opioid (KuKanich and Papich, 2004); however, there is a large variability in uptake, and the author finds it has efficacy in cats only. In dogs, the author would never use tramadol alone for treating chronic pain as it may alter behaviour without treating pain, thus making pain assessments challenging and potentially misleading.
In cases of severe pain flare-ups, the author will consider hospitalisation and the administration of opioids and local anaesthetic techniques to gain control of the pain. This should also prevent further central nervous system alterations that may facilitate the pain pathways.
Adjunct treatments
Physical therapies, such as physiotherapy, hydrotherapy, massage and acupuncture, should all be considered as part of the approach to chronic pain management. Clinicians should also discuss with the owners the use of physical aids to help patients perform normal functions, such as sleeping, exercising and toileting, where necessary.
Physical therapies, such as physiotherapy, hydrotherapy, massage and acupuncture, should all be considered as part of the approach to chronic pain management
Nutrition is also an aspect of case management that might be worth considering, especially with nutraceuticals having the potential to influence the disease progress (Martello et al., 2019). In fact, there is evidence of the benefits of oral supplementation with omega-3 fatty acids found in some fish oils and green-lipped mussel extracts for the management of osteoarthritis-related pain (Roush et al., 2010; Bui and Bierer, 2001).
What is the future of chronic pain management?
Many reports describe the possible beneficial effects of cannabidiol (CBD) on pain in humans, although there are limited large-scale controlled trials. The situation is similar in small animals, with a handful of small-scale studies published, with mixed overall results (Brioschi et al., 2020; Gamble et al., 2018; Mejia et al., 2021). In addition, there are currently no licensed CBD preparations available for the treatment of pain. At present, CBD therapy should be considered as an adjunct treatment only, and owners should be encouraged to seek professional guidance if considering CBD treatment for their pets.
Nocita is a liposome formulation of bupivacaine (a local anaesthetic) which, when infiltrated into soft tissues, provides 72 hours of analgesia. However, it is only licensed in the USA for dogs and cats. It is likely that there will be a growing interest in sustained-release formulations of currently available opioid analgesics and NSAIDs, which may offer flexible, at-home treatment options for owners.
Summary
There is currently no “magic bullet” available for treating pain states in companion animals, and it is unlikely that such an agent will ever exist. To adequately control pain, it is necessary to be aware of the underlying cause, the chronicity of the condition and the effects of the available agents on the patient’s quality of life and pain experience. Multimodal approaches that include adjuncts are likely to be more successful than a monotherapy approach, and it is essential to involve the owner in the decision-making process as their input will be essential to the long-term management of cases.
Multimodal approaches that include adjuncts are likely to be more successful than a monotherapy approach, and it is essential to involve the owner in the decision-making process
Research into pain recognition, causes and therapies is a growing area that will undoubtedly produce new and exciting breakthroughs in pain medicine. This will ultimately allow better job satisfaction for veterinary professionals, ease of mind for their clients and, most importantly, improved welfare for our pets.
