Fentanyl is very effective for pain, but to my knowledge has no potential “off label” benefit for cancer treatment, palliative or otherwise, unlike Metacam. I do know that cats and dogs react quite differently to certain medications, and some that are quite good and very safe for dogs, are problematic for cats.
I honestly can only speak for my own dog, Woody, who passed away in October of 2007. Metacam was a godsend for him, and it, in part, enabled us to have a year together that we otherwise would not have had. He was happy as a clam, and had better mobility and higher spirits during the time of his treatment, right up to his death, than he had had for at least a year prior to that point. I loved him dearly, and still do. I did everything I could for him, short of making him feel any more discomfort than he already did. A “cure” for him was out of the question, as the cancer had metastasized when discovered, so we/I chose the palliative route. I don’t regret it at all.
The Metacam issue for cats is very different from dogs. Cats have special problems dealing with any NSAID.
There are three versions of Metacam http://www.metacam.us/index.lasso?page=matrix&GUI=gui_1 . Oral metacam is labelled for “dogs only”, and with good reason, as it is designed for repeated home use. There are two different pacakges of Metacam for injection, one for cats and another for dogs — the contents are identical except for a small difference in sodium chloride concentration, but the issues are so different for cats vs. dogs that the manufacturer has been required to have two different products with completely different package inserts. The insert for the cat product includes strong warnings that are not included in the insert for the dog product, including in bold face type “Do not administer a second dose of meloxicam. Do not follow meloxicam dose with any other NSAID.”
The bottom line is that the manufacturer’s information is that oral Metacam is not to be used in cats AT ALL, and injectable Metacam should be used in cats only as a single dose. There are just hundreds of horror stories out there about vets using both oral and injectable Metacam in cats in multiple doses, and leaving cats with severe kidney failure, and often very quick death. In some cases this has occurred after only a single dose in accordance with product labelling, but more often it has resulted from using Metacam in a cat in ways that it is only properly used in dogs. It’s really best not to use Metacam in cats at all, since there are other painkilling options that don’t carry the risk of Metacam-induced kidney damage and the suffering (both cat and human) that accompanies it.