VETERINARY surgeons may no longer have to rely on non-steroidal anti-inflammatory drugs to treat chronic pain in their patients, Professor Duncan Lascelles told delegates at the VET Festival.
The professor, who trained at the Bristol veterinary school and now heads the department of comparative pain management and surgery at North Carolina State University, said there will be exciting new options available soon to treat intractable conditions like canine osteoarthritis.
Currently, NSAIDs are the only licensed medical treatments for chronic pain in veterinary patients but two new treatments are likely to receive authorisation in both the US and Europe by 2016 or early 2017.
The first is a compound called Grapiprant, being developed by the US biotechnology company Aratana. This is an EP4 receptor inhibitor and therefore targets an entirely different pain pathway to any agent currently on the market. The drug is also being tested in people but is likely to be available for use in veterinary patients before it reaches human pharmacies, he said.
Prof. Lascelles said that the data available from trials so far appeared “very positive” and indicated that it was effective when given as a daily oral treatment for chronic or, what he prefers to call maladaptive, pain.
However, further studies would need to be carried out to determine whether the drug has any of the toxic side-effects like those which may occur in patients receiving NSAIDs.
The other possibility was one being studied in trials by Prof. Lascelles’ group. This targets an important cytokine involved in maladaptive pain conditions called NGF (nerve growth factor).
A single injection of anti-NGF antibody has been shown to demonstrate “robust positive effects” in improving mobility in dogs badly disabled by osteoarthritic pain. The response is far greater than that expected from NSAID treatment and lasts for at least 28 days after treatment – “which is a very exciting result”, he said.
As the antibodies have to be species- specific, a felinised version of the same therapy has been developed and shows similar encouraging effects on mobility for up to nine weeks in cats, he added.
Long-term efficacy was particularly important in this species: “We won’t need to rely on the owner having to struggle with the cat to give its medication and so this gives us a treatment that will not disrupt the owner’s bond with their pet.”
Prof. Lascelles explained how research was providing an increasingly detailed understanding of the causes and potential treatments for chronic pain in humans and animals. It was also revealing some of the subtle effects that long-term pain can have throughout the body.
Conditions like osteoarthritis affecting the joints will cause significant changes to other body systems. That includes the brain: “This will shrink in response to chronic pain. The parts of the brain that are worst affected are those involved in cognition. The good news is that those changes can be reversed with effective treatment,” he said.
In the meantime, clinicians could make much better use of the options that are already available – such as NSAIDs. There is a tendency still among practitioners to use these drugs as re-brigade treatment, given as a short-term measure in response to signs of chronic pain. However, that means that the agents are never being used most effectively, he said. The drugs should be given much earlier in the disease process and the patient should remain on a maintenance dose for much longer.
