American Board of Internal Medicine (ABIM) Certification Practice Exam

Which medication is known to potentially cause osmotic diarrhea?

1. NSAIDs

2. Colchicine

3. Magnesium sulfate laxative

4. Carbamazepine

The correct answer is: Magnesium sulfate laxative

Osmotic diarrhea occurs when certain substances in the intestine draw water into the bowel, leading to loose stools. Magnesium sulfate is a well-known osmotic agent commonly used as a laxative. It works by attracting water into the intestine, which increases the volume of the intestinal contents and induces bowel movements. When magnesium sulfate is ingested, it remains in the intestinal lumen and holds onto water, leading to an increased stool volume and the potential for diarrhea. This mechanism is distinct from that of other medications, such as NSAIDs or carbamazepine, which do not primarily exert their effects in this fashion. Colchicine, while it can impact gastrointestinal motility and may lead to diarrhea, is not classified as an osmotic agent. Therefore, magnesium sulfate laxative stands out as the medication that explicitly promotes osmotic diarrhea due to its ability to hold onto water in the gastrointestinal tract.