Which of the following would not be classified as an antidiarrheal drug?

The correct choice is bisacodyl, which is classified as a stimulant laxative rather than an antidiarrheal drug. Antidiarrheal medications are designed to reduce the frequency of bowel movements and alleviate diarrhea by acting on the intestinal tract. In contrast, bisacodyl increases intestinal motility, promoting bowel movements, and is typically used to treat constipation.

The other options provided, such as Imodium (loperamide) and diphenoxylate, are both effective antidiarrheal agents. Loperamide works by slowing down gut movement, allowing for more water absorption, thereby reducing the frequency of stools. Diphenoxylate is also used for its similar action in treating diarrhea. Thus, these three options directly address symptoms of diarrhea, while bisacodyl does not.