2. Acute diarrhea or constipation in the 7 days before the predicted first study day. If screen occurs >7 days before first study day, this criterion will be determined on first study day. Diarrhea will be defined as the passage of liquid feces and/or a stool frequency of > 3 times per day. Constipation will be defined as a failure to open the bowels more frequently than every other day