Cornela,
The FDA has approved Metacam for cats, the use varies. If you can give me the dose you have been giving (and read the box for the mg/ml) I can tell you if it was above the recommended dose, but metacam is used with cats.
You need to remember as well that all animals/humans respond differently to medications. People can go into liver failure with simple Tylenol...so there is never a 100% guarantee with anything. I am sorry you are dealing with this. I have read of another case of a cat going into kidney failure but responded well to treatment.
Again, if you want to know if the actual dose is correct, please respond.
Dr.Vamvakias
Dr. D.A. Vamvakias
Veterinarian