What is the first-line medication prescribed for a client preparing for a colonoscopy?

Polyethylene glycol 3350 is the first-line medication prescribed for a client preparing for a colonoscopy due to its efficacy as a bowel-cleansing agent. This osmotic laxative works by drawing water into the intestines, which helps to soften the stool and increases the frequency of bowel movements. The goal of using polyethylene glycol in this context is to ensure that the bowel is completely clear of any stool, allowing for a thorough examination during the colonoscopy.

Other medications, such as docusate (a stool softener), loperamide (an anti-diarrheal), and famotidine (an acid reducer), do not serve the primary purpose of bowel preparation. Docusate is often used to prevent constipation rather than to prepare the bowel for a procedure. Loperamide is used to control diarrhea and would counteract the objective of clearing the bowels. Famotidine is used to reduce gastric acid and is not indicated for bowel preparation. Therefore, polyethylene glycol 3350 is the appropriate choice for ensuring optimal conditions for the colonoscopy procedure.