Hi,
Can you tell me how long ago your cat ate the tablet? If it was recently you need to get her to vomit immediately. The dose she got is extremely high for a cat and can cause many problems. She very likely will start acting like she is hallucinating and her heart will be racing. Her blood pressure may drop to dangerously low levels, as can her breathing. If she doesn't vomit at home (give her 2 teaspoons of hydrogen peroxide), then you should take her to an emergency vet for them to administer something to make her vomit. She may also need to be treated with a drug called NALOXONE, which is the antidote for oxycontin.

I just read the rest of your question. There are much better pain medications for your cat after his surgery. If your vet didn't send anything home with you, ask about Metacam, buprenorphine, or tramadol.

Please let me know how she does or if you have other questions!
Dr. ScarlettDr. Scarlett39806.1290299421