Welcome to the Chinchilla Club Forum!
Do keep in mind we are not vets, only owners and breeders of chinchillas that we dearly love. What we tell you is what we have done in the past and found to work, the ultimate decision is yours to make.
If he is not eating or drinking he is probably going into dehydration and/or is impacted ... neither of which is good.
Impacted is when the digestive tract stops because it has no flora to keep it moving. His bowls get stopped up ... This makes the chin think it is full, and not hungry. The only thing I know of that works, once a chin that is impacted, and there is no guarantee, is to give him an almond or two (This is the only time you will see me suggesting a nut of any kind for a chinchilla.) This happened to a friend of mine chinchilla and when it finally pooped it was all stuck together making a 3 and 1/2 inch long poop.
Antibiotics kill bacteria ... that is it's job ... BUT ... it kills all bacteria the good and the bad. The good bacteria is often referred to a flora. Flora helps to digest the chinchilla's food and keeps the digestive tract moving ... this is a must for all animals, even humans, but especially so for chinchillas. Once their digestive tract shuts down, they can go down quickly.
Please read: Don't let the Cure Kill Your Chinchilla at
http://www.geocities.com/jobernstein1949/ACureCanKill.htmlYogurt is good, it can be fed from a spoon or an eyedropper.
Yogurt is a milk product and must be given at least 3 hours before or after the dose of antibiotic. Mine like strawberry and blueberry yogurt best. I would give him as much as he wants , especially when given to him for this reason. Healthfood stores carry acidophiles, which can also be used.
How old is your chin?
Why is it on antibiotics?
What killed the first chinchilla? Not prying, just trying to help.
Jo Ann