Advil is slightly worse (kidneys) than Tylenol (liver). For cats Tylenol is deadly. One Tylenol will usual kill a cat. Most dogs can tolerate a couple days of Tylenol, but it's not recommended.

If you are going to give aspirin pre-treat with an acid blocker. For a large dog give 150 mg of Rantidine (Zantac) 2X daily, and for Med-small 74 mg 2X daily. For a tiny dog- ??? If possible start with the acid blocker 1 day before giving the aspirin. Aspirin has a high tendency to cause immediate stomach irritation, where the dog will start vomiting. Even buffered aspirin or Bufferin when given with food can make dogs nauseated.

These problems are why some Vet drugs in the Cox-2 inhibitor class came out. As discussed before the major trade names are: Rimadyl, Deramaxx, and Metacam. All can cause liver problems with Rimadyl being the worst. It also seems to relieve pain the most, and Vets prescribe it most often.