Christie Cornelius, DVM CHPV BluePearl Pet Hospice

The treatment of chronic pain conditions in pets generally requires long-term protocols.  Osteoarthritis (OA) is the most common chronic painful condition in geriatric cats and dogs and requires long-term treatment, as it is by definition a condition that does not resolve.  
Chronic use of medications increases the likelihood of experiencing known side-effects, encountering lesser-known problems related to medication, and resistance to medication administration.  This becomes even more relevant when chronic pain conditions such as osteoarthritis occur concurrently with other chronic conditions, such as renal, thyroid, or cardiac disease.  For this reason, a combination of pharmaceutical and non-pharmaceutical options are needed.

Opioid medications are the cornerstone of acute pain treatment.  There are limitations to long-term narcotic use, including side-effects such as inappetence, euphoria, and tolerance.  Opioids are typically considered very safe choices for concurrent conditions that often affect pets in hospice care, such as kidney disease and heart disease.
Non-steroidal anti-inflammatories (NSAIDs) are important cornerstones of pharmacological treatment of chronic pain across all species that reduce inflammation.  NSAIDs such meloxicam (Metacam), robenacoxib (Onsior), and prioxicam are most commonly used in pets diagnosed with chronic pain.  
Chronic kidney disease is fairly prevalent in geriatric pets, especially in cats > 15 years of age. In the past, veterinarians have shied away from recommending NSAIDs in aging cats with kidney disease, but newer research suggests that NSAIDS such as meloxicam may not be harmful, but in fact beneficial in cats with kidney disease when hydration status is maintained.  Gastrointestinal side effects such as inappetance, vomiting, and diarrhea can sometimes occur in pets with use of NSAIDs due to gastric ulceration.  Some veterinarians will prescribe omeprazole (Prilosec) to administer concurrently to prevent these issues. 

Gabapentin is an anti-epileptic that is utilized to treat chronic pain in people and pets.  Newer studies from human literature have recently shown gabapentin to be opioid-sparing and efficacious even for treating acute pain.  Gabapentin is now frequently prescribed to cats for use prior to veterinary visits to reduce anxiety and improve handling.  For cats and smaller dogs, compounding of Gabapentin is required.  There is a commercially available liquid for use in veterinary medicine that does not contain xylitol, which is used as flavoring in human preparations.  Xylitol is toxic to both cat and dogs, so the veterinary formula is the only safe liquid form of Gabapentin available. Side effects with Gabapentin are uncommon, and are generally sedation or mild gastrointestinal upset, although neurological weakness can be amplified during treatment.  
Amantadine is another orally available medication that is very attractive for the chronic pain patient.  Although robust studies in pets are lacking, amantadine’s injectable analog, ketamine, is being more widely utilized as a palliative treatment for pain in pets in hospice.  Amantadine works at the level of the spinal cord to reduce pain signaling and are more accurately viewed as anti-hyperalgesic rather than true analgesic drugs.  Clinical use of amantadine has been growing, and the drug has been associated with minimal side effects (occasional gastrointestinal upset) and has been well tolerated.
Other long-duration pharmacological treatments for OA include Adequan, joint injections, and emerging monoclonal antibody (mAb) therapies targeting pain pathways (such as nerve growth factor – NGF).  Adequan has long been appreciated to assist in joint-related discomfort in cats and dogs, and more recent data has expanded the use of it for the treatment of urinary bladder cystitis in cats.  Joint injections of hyaluronic acid, long-acting steroids, platelet rich plasma, and stem cells provide the benefit of a treatment that is almost exclusively localized, which limits impact on other organ systems.
Dietary supplements or ‘nutraceuticals’ available with some clinical data in cats and dogs include green-lipped mussels, glucosamine/chondroitin, MSM and omega-3 fatty acids.  Studies evaluating improvement levels and quality of life in pets fed a diet with these compounds revealed equivocal results, thus any improvement seen with these supplements is considered limited, and in some cases, subjective.  Dietary supplements are not regulated by the FDA, thus manufacturers are not required to provide scientific information to legal authorities for approval.  However, supplements are widely used, and many compounds in supplements may be effective.  Some data is emerging; however, without consistent evaluation methods and varying products/doses, FDA approval for these supplements is not in our near future.  Supplements being evaluated include, but are not limited to curcumin, amica, resveratrol, cannabinoids, and terpenes.
We’ve come a long way in veterinary medicine over the last four decades when it comes to recognizing and treating acute and chronic pain in pets.  Progress in research and education, along with an increased awareness of how our pets experience pain, will lead us toward more technologically advanced, effective and safer solutions to physical, emotional and mental suffering in our companions.