Hello, my name is***** and I have over 20 years of experience as a veterinarian. I'm sorry to hear that your little guy isn't feeling well and is lethargic, not eating or drinking and vomiting foam.
Vomiting foam means she is bringing up stomach/esophageal mucous that is mixing with air as he retches. This is not unusual when they vomit on an empty stomach. I suspect whatever led to his nausea and vomiting led to blood in his stool as well.
Vomiting and blood in the stool can be related to eating something he should not have, too many treats or table food
, eating foreign material (which could cause a partial gastrointestinal obstruction), chronic pancreatitis, a dietary allergy or sensitivity, toxin exposure, a viral or bacterial infection, inflammatory bowel disease, hyperthyroidism
(a tumor of the thyroid gland) internal organ failure (kidney
or liver disease or diabetes
), or even infiltrative cancers such as lymphoma.
You don't say how old your fellow is but in older cats we are more likely to see organ disease or cancer unfortunately.
Because he hasn't eaten normally in several days and was vomiting I am very concerned about him. If he still isn't drinking well either he will quickly become dehydrated, even with the fluids he was given. And as his liver breaks down fats for energy to live he may develop a type of liver disease called hepatic lipidosis.
Ideally he would see a veterinarian again if he isn't improving with the 24 to 48 hours with the suggestions I give you. They could re-examine him, run blood tests and possibly check radiographs and/or an ultrasound to evaluate him and know best how to treat him. Since you didn't mention testing I assume they thought to treat his symptoms and see if he improved, with a recheck if he didn't.
In the meantime while they wait for results they can administer injectable anti-nausea drugs and fluids to rehydrate him, and give an appetite stimulant.
At home to try and settle his stomach you can give either:
1) Pepcid ac (famotidine) at a dose of ¼ of a 10mg tablet per 5 to 10 pounds of body weight every 12 hours
2) Prilosec (omeprazole) at a dose of ¼ of a 10mg tablet per 5 to 10 pounds of body weight every 24 hours
These are acid reducers and may help him feel less nauseous so that he will eat and hopefully not vomit. They are quite safe and can be used for several days if necessary.
You can use a medicine syringe to try and force water, or low salt broth into him orally every couple of hours.
A couple of hours after giving the acid reducer I recommend offering meat baby foods or a bland diet of 2/3 boiled, minced, white skinless chicken and 1/3 boiled, white rice mixed with some low salt chicken broth to make it easy to lap up and swallow.
If he continues to not eat he should be rechecked.
Please let me know if you have any further questions.