Rimadyl and Duramaxx are similar products to Metacam (NSAID's). Rimadyl can have nasty side effects which is why we don't use it where I work. We do use both the other meds though.

If the Metacam is no longer working for your dog, and the dog is very old or has a terminal illness it's possible your vet may prescribe Tramadol. That is a very potent pain killer but normally only used for short term unless it's for a terminal or ancient patient that nothing else will work anymore.

Tramadol has it's share of side effects also, and dosing may take a couple times to get it nailed down but it may buy some time. My cat Dusty was on that for a short time before she went to the RB. Even though it's not approved for use in cats (very little is) it did help her when nothing else worked anymore.

It's worth at least asking your vet about, or if they prefer to use something similar.

Good luck.