A 67-year-old man with chronic diarrhoea due to short bowel syndrome is prescribed a medication to reduce stool frequency. Which medication would that be?

• A. Lactulose
• B. Loperamide
• C. Bismuth subsalicylate
• D. Codeine phosphate

Answer: (B)

Slowing intestinal transit to give more time for water and electrolyte absorption is the way to reduce stool frequency in chronic diarrhoea, such as after bowel resection.

Loperamide fits this goal because it acts on mu-opioid receptors in the enteric nervous system to decrease intestinal peristalsis and increase segmental contractions, which slows stool passage and makes stools more formed. It stays largely in the gut, so systemic effects and dependence are minimal—an important consideration for an older patient with chronic diarrhoea.

Lactulose would worsen diarrhoea since it’s an osmotic laxative. Bismuth subsalicylate has antisecretory effects but is less reliable for long-term control of stool frequency and carries risks like darkened stools and salicylate effects. Codeine phosphate also reduces gut motility but has greater systemic opioid effects and dependence risk, making it less suitable for chronic management.