Hello, My name is XXXXX XXXXX I have been a veterinary nurse for 26 years.Thank you for allowing me to assist you today.
I am sorry to hear that you cat may have gotten a Percocet. This is concerning as this contains acetaminophen . Acetaminophen is highly toxic to cats and can be fatal due to extensive red blood cell damage and liver damage which can all occur within-36 hours.
If there is any chance that he may have ingested this I would highly recommend taking him to the vet preferably tonight for blood work so they can see if there as been any damage to the red blood cells or liver. In many cases once symptoms occur it can be to late.
Symptoms you may see are pale, white or blue gums, orange or brown color urine and swelling of the face and or front legs. Click here for more on this
I really would not suggest waiting to see if he is out of the woods, while you may see signs of damage to the red blood cells within 48 hours it can take a few days to see signs of liver failure.
With this drug it really is better to be safe then sorry.
I hope this helps and you find that he did not eat the medication.
Please reply back if you have additional questions or concerns.