Hi Markus,
Thanks for your question.
I think it’s worth confirming that this is actually arthritis so performing radiographs would be a good idea. Most practitioners try to avoid NSAIDs in cats so instead they use painkillers which I would name but my license prevents me from doing so. I would recommend that you speak with your current veterinarian or your new veterinarian about this as an option, but I strongly recommend you diagnose the condition first. Consider the scenario where you are administering all of these products and it actually isn’t the right condition. It would be unfortunate.
I hope this helps.
Dr. Clayton Greenway