This is Dr. Christian. Welcome to JustAnswer. What problems did he have with the rimadyl?
There are several other drugs in the rimadyl family that I might have suggested but with those side effects I don't think they should be used in this case. Here are some other things to try:
Glucosamine and Chondroitin are supplements than can help prevent cartilage loss in the joints and slow down the progression of arthritis. They can also lessen the need for pain medications. They are given daily and can be found at your veterinarian's, in a pet store or online. They are very safe. Here's a link: http://www.petplace.com/drug-library/glucosamine-and-chondroitin-cosequin/page1.aspx
Omega 3 fatty acids, found in fish oil capsules at your local pharmacy, are also good for skin as well as joints. One capsule daily for life is necessary.
Adequan is an injection typically given twice weekly for 3 weeks or so then as needed afterward. It has minimal side effects and can be very effective in treating and slowing down the progression of arthritis. Here's a link about it:http://www.petplace.com/drug-library/polysulfated-glycosaminoglycan-adequan/page1.aspx
I have recently started treating a dog with adequan that did not respond to rimadyl. He is doing much better. The adequan might be your best option.
I'm sorry, I didn't see that you were already giving that. Curaflex is a Glucosamine/Chondroitin supplement so you are already using that treatment. Adequan is definitely the best chance to get quick relief.