Some of the antibiotics I take for sinus infections give me the side effect of diarrhea. Look on your prescription precautions sheet. Some tell you the diarrhea is normal. Others say to contact a doctor if it is really bad or continues long. For me Augmentin 875 is one of the worst offenders for this. I can have the symptoms even after completing taking it. Unfortunately, I have allergies to some other antibiotics so I end up on Augmentin alot. Also, the Post Nasal Drip from the Sinus infection will give me diarrhea as well. It is particularly bad in the morning when this is the case.

I can't speak for the Vytorin, but I have been on Prevacid (30 mg twice a day) for a long time and haven't had any side effects with it.