Sunday, June 21, 2015

Pain management in Pets

Question 
Should tramadol be used as a first line treatment for pain caused by osteoarthritis in cats and dogs?

Answer

Despite being unlicensed, and recently being reclassified as a Schedule 3 drug, Tramadol is a popular oral analgesic for the management of chronic pain in dogs and cats. Tramadol is a centrally acting synthetic analogue of codeine that has two different principle analgesic modes of action. Tramadol and O-desmethyl metabolites exert an agonist effect at opioid receptors as well as inhibiting norepinephrine and serotonin re uptake in the central nervous system (CNS) thereby modulating descending analgesia pathways. Reasons for choosing Tramadol for the management of osteoarthritis pain include a perceived lack of side effects, particularly in relation to NSAIDs, cost (it is cheap), and perceived efficacy.
However it is worth noting that the evidence base for Tramadol in both cats and dogs for the management of chronic pain is very weak to non existent, and owner reported efficacy of a treatment, due to the placebo effect, is not the most robust means to assess efficacy of an analgesic treatment.
The analgesia provided by Tramadol is dependent on the action of the parent drug (which provides mainly non opioid mediated analgesia) and the production of metabolites (which probably provide opioid mediated analgesia). However in dogs, metabolism of tramadol is very variable, with a range of different metabolites being produced. Furthermore, many dogs produce very little of the metabolite that mediates opioid analgesia, limiting the analgesic efficacy of the drug in these dogs.
Cats probably produce more of the metabolite that mediates opioid analgesia, which is advantageous, but on the other hand, the opioid like metabolite is probably also associated with more side effects (sedation, drowsiness, dysphoria, nausea).
Given the current evidence base for Tramadol, NSAIDs should be considered the first line treatment for osteoarthritis related pain in both cats and dogs. There are NSAIDs licensed for this indication in both species and a large evidence base to support efficacy. Tramadol should be considered a second line therapy, either in dogs and cats that are intolerant of NSAIDs or to support NSAID therapy in animals where NSAIDs alone provide inadequate pain relief.

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