Laxatives and Antidiarrheals

A 68-year-old man with a history of chronic kidney disease (eGFR 35 mL/min/1.73m²) presents with constipation for 3 weeks. He has been taking iron supplements for anemia and reports abdominal discomfort and bloating. On examination, his abdomen is soft but distended. He has no signs of bowel obstruction. His serum potassium is 5.8 mEq/L and serum magnesium is 2.4 mg/dL (normal 1.7–2.2). Which of the following laxatives is most appropriate for this patient?

Which of the following laxatives acts by increasing intraluminal osmotic pressure and is contraindicated in patients with renal failure?

A 42-year-old woman with irritable bowel syndrome (IBS) and recurrent diarrhea presents with 5–6 loose stools daily for the past 2 weeks, abdominal cramping, and urgency. She denies fever, blood in stool, or recent antibiotic use. Stool culture and C. difficile toxin are negative. She has tried dietary modifications without relief. On examination, she is afebrile with mild abdominal tenderness. Which antidiarrheal agent is most appropriate for her condition, and why?

Which antidiarrheal agent acts by inhibiting prostaglandin synthesis and is contraindicated in infectious diarrhea?