Hello, I am Dr. B, a licensed veterinarian and I would like to help you with wee Jess today.
I am glad that Jess is still eating and bright, but we obviously want to get this under control for him if it has been going on for a few days now and is this profuse. Now
when kitties start vomiting there can be a number of culprits. This includes bacterial infection, viruses, parasites, dietary indiscretion, sensitive stomachs, foreign bodies, and toxins. Since he is an older gentleman, hopefully we can put worries of him eating something he shouldn't have (i.e. toxins, trash, non-edible items like toys, rubber bands, etc) lower on our list of concerns for him.
And if we can do so, then you can try to monitor him at home with supportive care at this point. In regards XXXXX XXXXX Panacur, that would be fine to try at this stage as it would rule out our wormy differentials. This is something you can purchase OTC at your vets and some pet stores but do remember to have an idea of his weight so that you get the right dose for him.
Otherwise, if he is actively vomiting, I would rest his tummy for a wee while (~8 hours) and give it a chance to settle. Let him have access to water, but not huge volumes since overdoing it with the water can cause vomiting as well. If the vomiting does subside by that point, then tempt him with a small volume (a tablespoon worth to start) of a light/easily digestible diet. Examples of this would be boiled chicken, boiled white fish, scrambled eggs (made with water and not milk), meat baby food (do avoid the ones with garlic powder in the ingredients) or there are also veterinary prescription diets that can be used (ie Hill’s I/D or Royal Canin’s sensitivity). Now if he can keep the small amount down for, then you can offer a bit more after 30 minutes. And as he keeps it down, he can have a bit more, and so on. By offering a light diet, we are providing an easily digestible protein source for the compromised gut. And offering small volumes will again less the strain on the gut and give us a better chance of getting food down that stays down.
Furthermore, to address the associated nausea, you can trial him on antacid therapy. There are a number of antacids that are available over the counter and pet friendly. I would advise only treating with one, but the two I tend to recommend are Pepcid (LINK) or Zantac (LINK). These are usually given 20 minutes before food (to allow absorption) and of course you want to double check with your vet if your kitty has a pre-existing condition or is on any medications.
Since vomiting can quickly dehydrate a cat (and dehydration will make them feel worse and complicate their situation), do keep an eye on his water intake and hydration status. To check his hydration status to make sure he is not becoming dehydrated there are a few things we can test. One is whether the eyes appear sunken, if the gums are tacky instead of wet/moist, and whether they have a "skin tent" when you lift the skin. To see how to check these parameters for dehydration, you can find a wee video on this HERE. (They use a big dog but it makes it easier to see and the principle is just the same). If his hydration is good, then we do just want to make sure he keeps drinking (you can even encourage him to drink but offering fresh water or even low-sodium chicken broth. As well, the light diets and wet food all are highly water dense and will get some more fluids into him). But if you check these and are already seeing signs of dehydration, then that would be a red flag that you'd want to have him seen by his vet before this becomes an additional issue for him (to avoid it getting to a stage where he has to be hospitalized for IV fluids).
Since toxicities and foreign bodies lodged in his GI are less likely here, I would suggest that you rest Jess' s stomach, then try the above. If you initiate these treatments and do not see improvement over the next 24-48 hours or appears dehydrated already, then it'd be best to follow up with his vet so they can make sure there is nothing sinister afoot. The vet will be able to have a feel of him and make sure there are no GI obstructions or worries and will be able to cover him with antibiotics against bacterial gastroenteritis. Furthermore, they can administer anti-vomiting medications by injection to help settle Jess's stomach and get him back on track as quick as possible.
I hope this information is helpful.
If you need any additional information, do not hesitate to ask!
Remember that if you have any lingering questions or concerns, please reply so that we may continue our conversation. I will be happy to work with your further and do everything I can to provide you with the service you seek. Please remember to rate my answer when you are satisfied (with4-5 stars or a happy face) so that I may receive credit for my assistance. Thank you & have a great day. : )