I tried to reply to this earlier but the forum went down and it lost my reply. I have had two piggies with weight loss and mobility issues who have then been diagnosed with arthritis and gone on to use metacam at the lowest effective dose as maintenance.
Merry (RIP in my avatar) began to struggle with moving and lost weight after the death of his brother Pippin and when we got Suilven as tiny baby he struggled to keep up. He was diagnosed with arthritic hips and put on long term metacam, he has a totally new lease of life with meds and a new friend and had a very happy six-eight months before dying aged 6 having had a stroke.
Donald (RIP) was 3 and a half but was losing weight and bunny hopping/ avoiding activity. The vet diagnosed arthritis by x-ray (he was having one anyway to check teeth roots so we just had a look at the rest of him too) in his hips, knees and seriously in his wrists. He was also put on the lowest effective dose of metacam for long term use. His condition was a little more complicated in that he seemed to have an issue processing vitamin C and so was chronically deficient which leads to bleeding into the joint spaces and therefore a lot of pain. It turned out he needed 200mg (a humans worth and more than 4x the piggy dose) of vitamin C daily just to keep him ticking over properly! His scruffy coat and damp eyes and nose got much better with this increase in vitamin C. I would NEVER suggest using a dose like that without vet advice though. Dinky was a special case and it was very unusual for him to need so much. Unfortunately he died suddenly only weeks after these discoveries.
Long term metacam (or other anti-inflammatory) use is a balancing act. It will cause kidney damage in the long term but you need to balance this with the increased quality of life a piggy has whilst on meds. It is very much quality vs quantity. The kidney damage will shorten lifespan to some extent but conversely a piggy who is miserable and not eating or moving much will be vulnerable to many other problems that can cause premature illness or death. You need to have a good think and see what is the right thing for you and Star.
Lowest effective dose is always the safest. Use the smallest dose possible to relieve the symptoms and so minimise damage and increase longevity. It also means that if you need to, you can increase the dose. If you give the max allowed dose everyday, whether it is needed or not then you haver nowhere to go if there is a flare up, UTI or another problem that you would want to increase the dose for. We also used to give Merry days off meds every so often, not so much that he got sore but enough to give his system a break every so often.
Sorry for the essay but I hope some of this helps....