Why does my new kitten have diarrhea with occasional vomiting?

I purchased this kitten yesterday from Petsmart. He was listed as 4-5 months and healthy. He is up to date with his shots and tested negative for aids and leukemia. He has been very loving and active. He was sleeping with me last night and suddenly ran as fast as he could to the litterbox. He had diarrhea and made a real mess in and out of the litterbox. He has also had diarrhea twice today and threw up once today. I did change his food from purina kitten to science diet kitten when he came home yesterday. I didn't realize that I should have slowly adjusted him to the new food. Could this be the problem, or does it sound like something else? If it is the problem, should I just keep giving the science diet and ride it out, or should I start back with the purina and slowly add the science diet? Should I bring him to the vet tomorrow if things don't improve? Thanks in advance.

Jeremy

mmmhm that nice to know.

I had this problem with the first kitten I was fostering, and the shelter told me to switch the food back to the original brand, and when he is healthy I could try to slowly change it to the new brand. probably change the food back, then give your vet a call and ask if he needs to come in.

Its likely the food change, ive had at least a cat my whole life and currently have 3, whenevr you change the food it messes them up for a while, i wouldnt switch back and forth it could just make it worse. You could try mixing the 2 and gradually put less and less of the one you dont want anymore until his digestive system calms down. The vommiting could also be caused by eating too fast/ too much it happens from time to time with all cats, but the diarrhea should go away once hes used to the food and you should consult a vet if it doesnt.

Jeremy,
Congrats on the new family member! I work in the animal field and run across new adopters and this problem weekly. It very well could be the food. Take away the new food and give him the old with just a bit of the new food mixed in. It is quite a jolt to the system to change foods especially on one so young. Try mixing it slowly dont rush it. If he is not better in a few days take him in to the vet. If he develops more symptoms ie. runny nose goopy eyes lethargic... take him to the vet! hope things work out :)