Which of the following drugs is classified as a stimulant laxative?

Bisacodyl is classified as a stimulant laxative, which means it works by directly stimulating the nerves in the intestines to promote bowel movements. This type of laxative is particularly effective for relieving constipation and is often used when quicker relief is needed, such as prior to medical examinations or procedures. Stimulant laxatives like bisacodyl increase the rhythmic contractions of the colon, leading to a more prompt and effective evacuation of the bowel.

In contrast, the other options listed are not stimulant laxatives. Lactulose is an osmotic laxative that draws water into the bowel, thereby softening stool and stimulating bowel movements. Polyethylene glycol, also an osmotic laxative, works by retaining water in the stool to promote its passage. Methylcellulose is a bulk-forming laxative that adds bulk to the stool by absorbing water, which helps in stimulating peristalsis but does not have the direct stimulating effect as bisacodyl does. Each of these alternatives has its own mechanism of action, distinguishing them from stimulant laxatives like bisacodyl.