I have used Clavamox as an antibiotic after my cat had an operation.

Clavamox is basically Amoxicillin + clavulanic acid.

Pills can be kept at room temperature. The liquid form of the medicine should be kept in the refrigerator and not be used 10 to 15 days after opening/mixing it.

Opinions seem to diverge as to what happens if you keep the liquid in room temperature. Some say that it loses a significant part of its potency even after a couple of hours and some say that it is still good for up to 7 days.

However, according to this Amoxicillin can either be refrigerated or kept in room temperature, while Amoxicillin with Clavulanate needs to be or should be refrigerated. Both kinds of antibiotic can be taken on empty or full stomach.

For further info on Amoxicillin see here:
http://www.medicinenet.com/amoxicillin/article.htm
http://www.nlm.nih.gov/medlineplus/druginfo/medmaster/a685001.html

In my case I did not know that I had to keep it refrigerated and I had it in room temperature for 4 days, after which, realising my mistake, I put it in the refrigerator. The medicine was used for 6 days (after which I got a refill) and for as long as I was using it it seemed to have been working.