When a chin's system is full of food that has been digested, but not expelled and becomes impacted, it makes the chin 'feel' "full ". Many times, this is the reason they will not eat while on an anti-biotic ... besides being sick, they do not 'feel' hungry. *If you can get your chin on it's back (or wrap it in a towel), gently massage it's tummy and below ... if you feel the poops/feces in the intestinal tract between your thumb and forefinger ... your chin is, or is on it's way, to becoming impacted.
*If you know or even think your chin may be pregnant ... DO NOT massage the tummy area ... you could kill or damage an unborn kit/kits.
Why MOST vets will not caution you about the possibility of constipation (and it's complications) when your chin is on a medication and how to handle it, I do not know, but I wish they would!
Acidophilus or live culture yogurt is/should be used to replace the 'good bacteria' or flora in the system when a chin is on meds.
*PLEASE NOTE: Do NOT give yogurt and/or acidophilus at the same time you give your chin it's medication! Yogurt is a milk product and will destroy the properties of the anti-biotic and visa versa. Acidophilus will be of no use when given at the same time the meds are given ... the meds kill the bacteria immediately ... it is a live bacteria culture. Yogurt and/or acidophilus should be given about half way between the doses of medication ... usually about 3 to 4 hours apart. This gives both the meds AND the 'flora replacement' a chance to do their jobs.
I have found it best to put my chins on alfalfa hay (and discontinue the chinchilla pellets) while on an anti-biotic. Chinchillas can live on hay and water only, if need be. Alfalfa hay gives them the extra roughage a chin needs to keep his system going and the nutrients his body needs to survive. Always make sure your hay is fresh and does not smell musty or have any signs of meldew! Timothy hay is to be used when your chin is healthy. Fresh HAY is a necessity for a chin, ON A DAILY BASIS, sick or well.