I agree with the others, time for an increase. You don't want to hold a dose for longer than 6 cycles if she's only seeing yellow nadirs. From the protocol:
My Neko has arthritis too. There are several things you can do before going to Metacam. Before trying pain control, there are options for helping the joints that have arthritis. Fish oil (for Omega-3) is an anti-inflammatory and you can add that to each of her PM and AM meals. Not sure what types are available in Oz, but I've used both salmon oil and now I'm using something that contains herring and sardine oils. They are available in pet food stores here. Glucosamine chondroitin can also help. Here I can get it in Cosequin (available from the vet) or you probably get something at pet food stores too. Hyaluronic acid is another additive I'm using, specifically
Hyaflex. Yet another medicine that I've seen others from Australia use is
Cartrophen. Neko's getting an injection once a month for that. It does have a loading period where injections are more frequent. That's also something you get from the vet. It's specifically for dogs (and horses) but also used for cats. I get syringes preloaded from the vet and inject them myself. In the US, they use a very similar medicine call Adequan - it's not available in Canada, don't know about Australia.
Finally, once you've exhausted the above options, pain control is next. Neko is on a maintenance dose of buprenorphine, given twice daily. I get a vial with chicken flavour from the compounding pharmacy. They use Metacam in Canada too, some vets are less eager than others to try it. Even Neko's vet who is fairly conventional doesn't have it on her list of drugs to try. Her suggestions in order were bupe, gabapentin, then tramadol. I recently looked at the FDA list of complaints for veterinary drugs for felines and noticed half of them were for Metacam.