While both metacam and ibuprofen have the same mechanism of action (inhibiting COX enzymes) they are in different classes of NSAIDS and are not derived from the same drug compound.
The problem with some NSAID's is their ability to effect blood flow to the kidneys, and with different classes of drugs, or even large doses, these meds could cause kidney problems. This effect is dose dependent and also species dependent. In other words, this renal effect is more pronounced in certain species then others. For example, dogs can go on long term metacam with usually no effects (although veterinarians will still monitor kidney function via routine bloodwork- basically to check that the kidneys are eliminating unwanted metabolites effectively). However, in cats metacam is only given for short term pain management (eg. post-surgical) and their dose is much smaller. I have seen a cat go into acute kidney failure because the owner gave the wrong dose (gave WAY too much). The bottom line- the renal effects seem to be dose dependent- if you give the right dose you shouldn't have a problem- ALWAYS double check your dose and always follow the dose the vet prescribes- they know what is safe and the doses are calculated by a body weight formula.
I'm pretty sure that the reason ibuprofen is not prescribed for animals is that this renal effect is much more pronounced in this class of NSAID. But I'll ask my boss tomorrow (Who is a veterinarian that is an exotics specialist)
Hope this helps!
