Which medication is NOT used to treat diarrhea in patients?

Amitriptyline, a tricyclic antidepressant, is not primarily used to treat diarrhea. Its main indications include depression and certain types of chronic pain. While it has some anticholinergic properties that can help manage gastrointestinal symptoms, it is not a first-line treatment for diarrhea.

In contrast, loperamide is an over-the-counter medication specifically designed to slow down gut movement and reduce the frequency of diarrhea. Dicyclomine is an anticholinergic used to relieve bowel spasms, which can help in managing symptoms associated with irritable bowel syndrome and similar gastrointestinal disorders, including diarrhea. Metronidazole is an antibiotic effective against bacterial infections that can cause diarrhea, such as those resulting from Clostridium difficile.

Therefore, among the medications listed, amitriptyline is not recognized as a treatment for diarrhea, setting it apart from the others that have specific roles in managing this condition.