They have him on vancomycin, flagyl, and zosyn to cover their bases. It is quite likely that it's just the chemotherapy that has irritated/damaged the lining of his intenstines either causing his villi to slough off a bit or to release fluid. They are a bit puzzled that we haven't seen these symptoms before, as there were no new chemotherapeutics this round. My opinion of the matter is that it was just the concentration of the chemo that has been hitting him hard--after all, he's been throwing up for a week now. Although he has nasty GI symptoms, the good news is that the GI tract is one of the quickest places for healing in the body.
Andrew's taken a few sips of milk here and there, for which I am very grateful. I'm definitely breathing much easier as the PICU is becoming less and less likely of a possibility.