A 70-year-old man post-hip replacement on morphine and taking lactulose and senna, yet he has hard stools. Select the most appropriate laxative.

• A. Lactulose
• B. Naloxegol
• C. Senna
• D. Bisacodyl

Answer: (B)

Opioid-induced constipation is driven by morphine binding to mu receptors in the gut, which slows bowel movements and increases fluid absorption. When standard laxatives like an osmotic agent (lactulose) and a stimulant laxative (senna) don’t relieve the symptoms, therapy that directly blocks the opioid effects in the gut is needed.

Naloxegol is a peripherally acting mu-opioid receptor antagonist. It works in the gastrointestinal tract to reverse the constipating effects of opioids without affecting the pain-relieving action in the brain, so the analgesia from morphine remains intact. That targeted action makes naloxegol the most appropriate next step in this patient who remains hard-stooled despite conventional laxatives.

Lactulose and senna were already tried, and while they can help many patients, they don’t counteract the underlying opioid effect. Bisacodyl is another stimulant laxative, but without addressing the opioid receptor activity, it may be less effective in opioid-induced constipation.