Management of osteoarthritic and cancer pain in dogs and cats
DENVER, CO – With the development of contemporary pharmaceuticals, nutraceuticals, and other technologies, more pets are able to live reasonably comfortably despite chronic conditions. It is crucial to understand that appropriate pain management is good medicine, and that any barriers to pain management must be overcome in order to provide the highest level of care to our patients, explained Kim Spelts, CVT, VTS (Anesthesia), CCRP, CCMT, speaking at the American College of Veterinary Internal Medicine (ACVIM) Forum.
Osteoarthritis
Osteoarthritis (OA) is the most common orthopedic problem in dogs and cats, affecting about 20% of the population, with the incidence increasing with age. The typical presentation in dogs includes limping and/or lameness, stiffness when getting up or after rest that resolves with mild to moderate activity, and difficulty going up or down stairs and/or jumping into the car and on furniture. Cats with OA may have difficulty getting in and out of the litter box and as a result may urinate and defecate outside but nearby the box. They may also have trouble jumping to higher places. Ms. Spelts stressed that a multimodal approach should be taken to control pain in patients with OA, and this may include weight loss, controlled exercise and physical rehabilitation, pain relievers, nutrition, and possibly surgery.
Nonsteroidal anti-inflammatory drugs (NSAIDs) are key in the pharmaceutical management of OA pain. A CBC and chemistry panel should be run before starting any patient on an NSAID, and repeated in 2-3 weeks, and then every six months to one year if no adverse events are observed. Other pharmaceutical interventions may include tramadol, acetaminophen (dogs only), gabapentin, and amantadine.
In recent years, interest has focused on slowing the progression of cartilage degradation and promoting cartilage matrix synthesis. Several products are available, including Cosequin® (glucosamine HCl, low molecular weight chondroitin, and manganese) and Dasuquin ASU®, which may provide a pain-relieving effect similar to that of NSAIDs.
Hyaluronic acid (HA) has been shown to provide a cushioning effect within a joint, and an injectable product is available as an FDA-approved drug for use in horses (Legend®). Some practitioners have used this drug off-label as an IV and/or IA injection in dogs with OA. To date there are no FDA approved oral versions of HA.
CanEVA-K9® (Canadian Elk Velvet Antler for Dogs) has been shown to alleviate the clinical signs of arthritis in dogs and improve ground reaction forces. Studies also showed that dogs receiving CanEVA® had a significant reduction of muscle atrophy, suggesting a myotrophic effect.
Adequan® is an injectable polysulfated glycosaminoglycan (PSGAG) that has been investigated and approved for use in dogs and horses. A number of studies have demonstrated the drug’s ability to decrease cartilage catabolism and prevent adverse joint congruity changes.
Regenerative stem cell therapy (RSCT) has been used successfully in the treatment of OA pain. RSCT uses cells in a dog or cat's own fat tissue to help provide pain relief, essentially helping the body to help itself. In this therapy, a patient undergoes a short surgical procedure to harvest a small amount of fat. Mesenchymal stem cells derived from this fat are then reinjected intravenously and/or directly into the patient’s affected joint(s). Recently published data indicates improvement in pain and function in dogs whose elbows, knees or hips have been injected.
Cancer pain
Most pain related to neoplasia begins as a mild, acute pain, but it has the potential to progress to a mild to severe chronic pain state. Early intervention will help to prevent “wind-up,” or sensitization caused by repeated painful stimulation of peripheral nerves, which will make treating the pain long-term easier.
For cancers requiring surgical intervention, the importance of perioperative analgesia cannot be understated, and a multimodal approach should include an NSAID (unless contraindicated), infusions of pain medications (opioid, NMDA antagonist (ketamine), etc.) as well as the use of local and/or regional anesthesia techniques.
Ongoing pharmaceutical support is the cornerstone of cancer pain management. As the disease progresses, more aggressive pain management will be required. Keep in mind that individual variability exists in patients’ responses to drug therapy, so drugs within a category should be substituted before switching therapies altogether.
The administration of bisphosphonates has been shown to reduce pain and pathologic fractures in humans with osteolytic lesions.
Maintaining quality of life (appetite, activity, function, interaction with family) is key, stressed Ms. Spelts. She said that long-term palliative care must address end-of-life issues as the pain and/or side effects of the care are no longer manageable.
Physical rehabilitation
Chronic musculoskeletal pain often develops as a result of OA due to altered gait patterns. Ms. Spelts said that this pain may be managed with low-level laser therapy, neuromuscular electrical stimulation, massage therapy, and therapeutic ultrasound. Aquatic therapy provides an ideal low-impact exercise for dogs with chronic pain; the buoyancy of water reduces the load on painful joints and allows for more comfortable exercise. As well, water pressure can reduce swelling and edema, and water resistance is useful for muscle strengthening.
Pharmaceuticals used in treating chronic pain
NSAID administration is very common in small animal practice for treatment of both acute and chronic pain, but therapy should be avoided in patients with liver or kidney disease, those with a high likelihood of hemorrhage and/or low blood pressure, and those with gastrointestinal ulcerative disease. Because of the increased risk of GI ulceration, NSAIDS should never be administered together or with corticosteroids without at least a 4-10 day washout period. It is also recommended to treat with a GI protectant such as omeprazole or misoprostal during the washout period.
Tramadol is a synthetic, centrally acting analgesic and is useful for moderate-severe pain. It can serve to bridge the gap between NSAID administration and the addition of a potent oral opioid. Dosing in dogs and cats is generally 2-5 mg/kg 2-4 times daily.
Amantadine, an NMDA receptor agonist,may help with allodynia and opioid tolerance in patients with chronic pain. In humans, it has been used for neuropathic pain. The dose for dogs and cats is 3-5 mg/kg daily, usually for only 21 days.
Gabapentin is a structural analog of GABA (gamma-aminobutyric acid) and was originally introduced as an anticonvulsant. It appears to be best suited for the treatment of neuropathic pain. Dose ranges vary from patient to patient, anywhere from 2-40 mg/kg up to three times a day. Lack of responsiveness and drowsiness seem to be the most common side effects.
Acetaminophen may be used for short periods in dogs with breakthrough pain, for which the combination of an NSAID and tramadol is not effective. Acetaminophen can be administered to dogs at 10-15 mg/kg BID for up to 5 days. Acetaminophen should not be administered to cats due to inadequate cytochrome P-450 dependent hydroxylation.
Anecdotally, oral morphine seems to provide effective pain relief (0.5 mg/kg up to three or four times daily), with the most commonly reported side effect being constipation and anorexia. Oral oxycodone is also an effective drug for severe pain in dogs, and it may be less likely than oral morphine to produce dysphoria. Oxycodone is effective in dogs at 0.3 mg/kg PO BID-TID.
Ms. Spelts concluded by saying that pain control is good medicine. A multi-modal approach, and not just a reliance on NSAIDs, will provide optimum pain relief. She stressed that veterinarians and technicians are the best advocates for a patient’s wellbeing, and that in more challenging cases outside help may be needed. CVT
