Long term pain relief is a touchy subject. I found an informative article for you:
There is evidence for pain relieving effects as an enhancement to analgesics in dogs for amitriptyline
(Elavil Rx) and for imipramine (Tofranil Rx). The recommended dosages in "Small Animal Clinical
Oncology" by Withrow and MacEwen is 1-2mg/kg every 12 to 24 hours for amitriptyline and 0.5 to
1mg/kg every 8 hours for imipramine. The effect is postulated to be partially due to seritonin
re-uptake inhibition so it is possible that fluoxetine (Prozac Rx) and similar SSRIs would also
provide similar enhancement to analgesic effects.
I found a case report on the use of gabapentin (Neurontin Rx) for pain relief due to neuropathic
pain. This is apparently the most common use for this in people but isn't yet a common use in pets.
Pain associated with shingles and with diabetes are examples of neuropathic pain in humans. I do not
know for sure if it would be helpful in chronic osteoarthritic pain, or not. I don't see any reason not
to try it if you find yourself looking for something different than amitriptyline.
Carprofen (Rimadyl Rx) has been the most consistently beneficial non-steroidal anti-inflammatory
medication for the pain associated with osteoarthritis in our practice. We have reasonably good
success with etodolac (Etogesic Rx, Lodine Rx) as well. I usually start out with aspirin first but it
sounds like you are beyond that point. When carprofen and etodolac don't work well enough we
usually add an opiod medication. I usually start with hydrocodone or codiene but we use morphine in
some dogs. I like the sustained release morphine (MS Contin Rx) really well but it is expensive
compared to morphine. The difference in using the medications is that morphine probably only works
4 hours or so and MS Contin works for 8 to 12 hours. For many dogs several hours of pain relief is
enough to make the day livable, so there is some value to regular morphine twice daily, if that is all
that can be managed. We try to hold off on opiod medications until late in the arthritis process but
they can be used for short terms, intermittently, to provide a period of really good pain relief to cut
down on the depression factor that seems to come with chronic pain. In dogs, since we control the
medication dosages, addiction is probably less of an issue than it is in humans, too.
Ancillary treatments that might help include glucosamine and chondroitin administration (500mg/day
and 400mg/day per 25 lbs of body weight), omega n3 fatty acid administration (3V Capsules tm, for
instance), and Vitamin E (400 to 2000U per day).
Keeping weight down to the ideal weight, or slightly below it, probably helps more with arthritis than
most medications. Moderate sensible exercise on a regular basis seems to help a great deal, too.