My two cents...Mimzy was prescribed metacam from age 3 for early onset arthritis and I fully believe had he not been on it his head tilt would have been fatal. He took it to the end of his days (he was debilitated by a stroke or some such eventually) and although I think testing his blood showed elevated levels of something kidney related it never slowed him down. He took an extremely high dose each day twice a day and it helped him immensely.
My dog, Jenna, on the other hand has been on it exclusively for arthritis pain and glaucoma relief since March and I can already see it's not as beneficial to her as it was to Mimzy and her kidney values are already taking a hit. Rabbits can clear the medication from their systems faster than other mammals was my old vet's explanation for the difference.
Also we have 3 brands here: Metacam (name brand) Ostilox (loxicom, I think), and Meloxidyl...and of the two knock-offs/generics we've been forced to use due to the Metacam shortage, only Ostilox does anything to relieve Jenna's pain. Historically, Metacam is by far the best for her as she always did well on it, and my vet is exasperated with me because it's the one I want for her. We've gone around all last week on why it's more effective (in my opinion having seen the results in my animal.)
Plus the Meloxidyl, I'm convinced, has something in it that aggravates Jenna's chronic pancreatitis. So I think brands are different in some small way and particular in effect to the individual patient.
Couldn't get the vet to agree about this yesterday when I took Jenna in for a checkup and put the matter on the table after a very trying weekend of Jenna being very uncomfortable despite regular dosing of Meloxidyl. But we don't have our beloved Dr. J anymore so everything's an argument. The vet we saw also believes any animal taking NSAID's will see g.i. ulcers from the first few months after beginning the therapy and attributed her discomfort to that. Okay, then she should be just as painful on the Ostilox with that logic, but she is not. His conclusion doesn't explain the lack of effect from one brand that is supposed to contain the same medicine as the others, so it has to be an additive that's causing issues. Keep this is mind if you have to change brands and one is not having the same effect as another.
Mimzy also never had any trouble with metacam, that bunny had a cast iron stomach. But I think both Pip and Fiver could get some upset from it so it was imperative it was given at mealtime or with a protective agent for the stomach if they weren't eating. I never used Ostilox or Meloxidyl with them so have no comparison there.
If this is more confusing than edifying I apologise. This just happens to be the burr in my saddle lately and I'm curious too to see if anyone else is having this kind of concern with NSAID pain relief for their pet.
On the subject of regular bloods being drawn, well Jenna is a particularly hard stick so I try to minimize the times she's having a visit from the vampire.
Sadly, as it's already been mentioned, by the time kidney issues surface, it's simply too late to change the inevitable.
ETA: CBD oil is highly controversial here for animal medicine. I would love to try it on Jenna, I know several people who swear by it, but the possible chance that it could raise her IOP rather than lower it or mess with her liver function is the reason I don't do it. My vet is very much against using it, probably due to it having no proper testing or science behind it's claims when it comes to giving it to pets. Until and unless I can see definite answers to what it can and cannot do or how it affects an animal in my care, it doesn't go past their lips.