There are a myriad of concerns for Puck at this point.
The first thing we need to be worried about is liver failure. Without eating normally, a cat's liver will begin to start failing in about 3 days time. When they stop eating entirely, the risk increases drastically.
The second concern is for dehydration, because he's not drinking well.
Finally, we have to worry that an underlying condition has caused all of the symptoms. At 17 years of age, he's at risk for quite a few health concerns including kidney disease, liver disease, diabetes, hyperthyroidism, etc.
I would highly recommend that you reach out to this family just as soon as you can and try to get Puck to a veterinarian. This is going to be is best chance at survival. If the family feels that its his time, humane euthanasia would be more kind than allowing his body to slowly fail.
At home, there are some things that you can try. The first thing is to administer a dose of regular pepcid (famotidine) every 12-24 hours. You will want to give 0.5mg/pound of body weight (a 10# ***** would receive 5mg, a 5# ***** would receive 2.5mg, etc). For this, you can buy the brand name Pepcid, or you can use the cheaper, off-brand “famotidine” that’s available. Either will be useful. 2 hours following this, try some pureed baby food in chicken or turkey flavors to see if he's interested. You may need to place a small amount into his mouth to stimulate his appetite. You can also offer pedialyte or low sodium chicken broth if he's interested in either of these.
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