First, just in regards ***** ***** you asked initially, it is important to know that Aspirin is not a pain relief we use in cats (its only used as a blood thinner in heart failure cases). As well, none of our OTC anti-inflammatory medications are cat safe. That all said, if we are facing appetite loss, we'd not use an anti-inflammatory anyway since that would not address the issue and only risk giving him a stomach ulcer.
Now based on his anorexia, we do have a few concerns. If he has ingested something non-edible or toxic, these could be to blame. Though we can also see this associated with dental disease (or any oral issue causing pain/discomfort), GI infections (ie bacterial, viral), pancreatitis, and general dietary indiscretions. As well, though less likely if his bladder is comfortable when you press on his belly, we can also see these signs in cats with urinary blockages (less likely here, but we may need to keep him indoors as we monitor him to ensure he can pass urine).
Otherwise, in regards ***** ***** care options you can try, you can focus on the nausea side of our concerns. To do so, you could start him with an antacid. Common OTC pet safe options would be: Pepcid (More Info/Dose @http://www.petplace.com/article/drug-library/library/over-the-counter/famotidine-pepcid) or Tagamet (More Info/Dose Here @ http://www.petplace.com/article/drug-library/library/over-the-counter/cimetidine-hcl-tagamet)
Whichever you choose, we’d give this 20 minutes before offering food to allow absorption. Of course, do double check with your vet if he has a known health issues or is on any medications you haven't mentioned.
Once that is on board, we can try tempting him to eat. Favorites are allowed, but we can also use light diet options like boiled chicken, boiled white fish, or meat baby food (as long as its garlic/onion free). Of course, if he cannot be tempted and since he isn't vomiting, we could also star syringe feeding here. For that, we can water down calorie rich diets (ie Hills A/D, Royal Canin recovery diet, even canned kitten food) or use a liquid diet (ie Clinicare, Catsure). As well, there are paste supplements (ie Nutrical) that can also be used. And these will all get more into him per bite even if we cannot get much in. So, if he cannot be tempted, then we'd want to start those to break his fast (especially as cats can develop fatty liver syndrome if off their food too long).
Since dehydration is a risk with his refusal to drink, we need to keep a close eye on his hydration. To check this and ensure he’s not becoming dehydrated, there are a few things you can test. Further to checking for gum moisture, you will want to make sure his eyes are not looking sunken and that he doesn’t have a "skin tent" when you lift the skin. To see how to check these parameters for dehydration, you can find a good video HERE (http://www.ehow.com/video_12232503_dog-dehydrated.html). If you are seeing any signs of dehydration already, then that would be our cue to have him seen before this becomes an additional issue for him (especially as it is often dehydration that makes them feel unwell).
Again since he has no vomiting, we can syringe fluids too. To do so, we can use plain water or unflavoured Pedialyte or Lectaid (which is ideal as it also has electrolytes) . Whichever we use, we'd aim to give a total daily volume of 48ml per kilogram of his weight. Of course, this would be divided into multiple offerings over the day, could include what you use to water down his food, and can be used as long as we don't cause him to vomit (since that would be counterproductive).
Overall, a wide range of agents could trigger the GI upset we are seeing. Therefore, in his case, we’d need to tread with care. So, it'd be ideal to keep him and start the above. If he struggles to keep anything down, doesn't appear to be passing urine, or doesn't start to respond within 12-24 hours; then we'd best to have him checked by the local vet.They can assess his hydration, rule out toxins, and make sure there is nothing in his stomach that shouldn't be there.Depending on their findings, his vet can treat him with injectable anti-vomiting medication, appetite stimulants, fluids, +/- antibiotics to settle his stomach and get him eating before he can just waste away.
All the best,
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