Hi! Excellent question.
Metacam is a non-steroidal anti-inflammatory (NSAID). It is widely used in feline veterinary medicine (I use it myself).
However, your concerns are certainly grounded in that metacam can be dangerous to cats. It has been associated with acute renal failure in cats. But if used properly it can also be very safe and certainly very useful in many situations.
There are some cats that should NEVER be given metacam:
1. Dehydrated cats
2. Any cat with a history of renal disease
3. Any cat whose renal values are currently elevated
4. Older cats with unknown renal values
These are the guidelines I personally like to follow (I'm a conservative here). In a young, relatively healthy cat, I will give oral metacam (1.5 mg/ml) at a dose of 0.1 mg/kg once a day for 3 days (total of three doses) OR 0.1 mg/kg every other day (total of three doses).
Even in a worse case scenario, I will not give metacam for more than 5-6 days total without checking kidney values and hydration status of the cat.
Let me repeat myself to say that metacam can be very helpful. It is the safest non-steroidal medication available for use in cats. Truth is, there just isn't any really good, really safe NSAIDS for cats so we make due with what is available.
I hope this helps! If you have any more questions please feel free to ask. Thanks for asking and good luck with your kitten!