NoNo, could be the meds or it could be the food. One of mine can't eat anything but the food she came with (wet OR dry) without being a little...icky...in the litter box.
if she's on antibiotics, I don't see how they're any different than us. There are plenty of probiotic supplements for pets these days, I would give that a try. Oh, and don't try yogurt, I once gave my older one yogurt, and it came out the same consistency...