Thank you for the reply.
If he has been vomiting for over 24 hours and if he is not eating or drinking, it is time for veterinary intervention. There are very many reasons why cats vomit, some more serious than others. Vomiting is a vague sign that can be associated with simple things like dietary indiscretion to more serious things like intestinal obstruction or metabolic disorders. In young cats, we usually are a little more worried about foreign body ingestion. We decide how aggressive we need to be in diagnosing and treating it based on how severe the symptoms and how long it has been going on.
In his case, I would be concerned in that it is going on without resolution for so long. It definitely warrants at least an exam and probably some bloodwork or xrays. The exam may help to rule out obvious things like intestinal masses, but bloodwork is needed to rule out metabolic changes like diabetes, thyroid or kidney disease or pancreatitis. Xrays will help to rule out an obstruction. It is not uncommon for all of these tests to be normal and there can still be GI disease present. Inflammatory bowel disease (IBD) is a very common cause of vomiting in cats. If your vet suspects this, they may offer a trial of medication or a change in diet to see how he responds.
Additionally, after a bout of vomiting, his gastric lining is obviously inflammed and needs a rest. Usually a 12-24 hour fast will help, but anti-vomiting medications are often needed to help insure the vomiting stops, whatever the reason. Zantac is an antacid, and can help decrease gastric acid, but is not very effective to decrease vomiting or nausea. On top of that, When a pet is vomiting, any medication is best given by injection so as not to irritate the gastric lining further. Fluid therapy can best be offered with IV fluids or fluids given under the skin (SQ) so that he does not get dehydrated.
With his history of a sensitive stomach, he very probably is a candidate for having inflammatory bowel disease (IBD). If that is the case, the goal becomes more management than cure and the signs will likely flare up intermittently as time goes on without some sort of management, but it is best to make sure we are not missing something more acute like a foreign body or a mass.
I hope this is helpful. Please let me know if you have ANY other questions. My goal is to give you 100% satisfaction and if you are not yet satisfied, please reply so I can clarify for you.